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Severely impaired adult brain neurogenesis in cyclin D2 knock-out mice produces very limited phenotypic changes
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Severely impaired adult brain neurogenesis in cyclin D2 knock-out mice produces very limited phenotypic changes Robert K. Filipkowskia,⁎, Leszek Kaczmarekb,⁎ a b
Behavior and Metabolism Research Laboratory, Mossakowski Medical Research Centre, Polish Academy of Sciences, Pawinskiego 5 St., 02-106 Warsaw, Poland Laboratory of Neurobiology, Nencki Institute of Experimental Biology, Polish Academy of Sciences, Pasteura 3 St., 02-093 Warsaw, Poland
A B S T R A C T The discovery of new neurons being produced in the brains of adult mammals (adult brain neurogenesis) began a quest to determine the function(s) of these cells. Major hypotheses in the field have assumed that these neurons play pivotal role, in particular, in learning and memory phenomena, mood control, and epileptogenesis. In our studies summarized herein, we used cyclin D2 knockout (KO) mice, as we have shown that cyclin D2 is the key factor in adult brain neurogenesis and thus its lack produces profound impairment of the process. On the other hand, developmental neurogenesis responsible for the brain formation depends only slightly on cyclin D2, as the mutants display minor structural abnormalities, such as smaller hippocampus and more severe disturbances in the structure of the olfactory bulbs. Surprisingly, the studies have revealed that cyclin D2 KO mice did not show major deficits in several behavioral paradigms assessing hippocampal learning and memory. Furthermore, missing adult brain neurogenesis affected neither action of antidepressants, nor epileptogenesis. On the other hand, minor deficits observed in cyclin D2 KO mice in fine tuning of cognitive functions, species-typical behaviors and alcohol consumption might be explained by a reduced hippocampal size and/or other developmentally driven brain impairments observed in these mutant mice. In aggregate, surprisingly, missing almost entirely adult brain neurogenesis produces only very limited behavioral phenotype that could be attributed to the consequences of the development-dependent minor brain abnormalities.
1. The phenomenon of the adult brain neurogenesis The term adult brain neurogenesis refers to generation of new neurons (due to the proliferation of precursor cells and their differentiation) in the brains of adult animals. Adult brain neurogenesis is limited mostly (although not exclusively) to two populations of dividing cells: (i) those in the subventricular zone (SVZ), with their progeny migrating through the rostral migratory stream to the olfactory bulb, and (ii) those in the subgranular zone (SGZ) of the dentate gyrus (DG) of the hippocampus. Those cells mature into olfactory bulb granule cells and DG granule cells, respectively. In mammals, this phenomenon was initially observed several decades ago, mostly in rodents (Altman and Das, 1965; Altman and Das, 1966; Messier and Leblond, 1960; Messier et al., 1958; Smart, 1961), but has gained paramount recognition over the last two decades, since seminal study by Eriksson et al. (1998) performed on human subjects. In human brain, substantial hippocampal neurogenesis is observed with no detectable olfactory bulb neurogenesis, but with continuous addition of new neurons in the striatum (see Bergmann
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et al., 2015, for review). The term neurogenesis encompasses a cascade of phenomena, starting from proliferation of the neuronal precursors, through their migration and differentiation. The most often used approach to measure the phenomenon is immunocytochemical detection of bromodeoxyuridine (BrdU) in the cell nuclei. BrdU given systemically replaces its natural analogue in DNA, thymidine, with its incorporation being the most massive during the S phase (DNA replication) of the cell cycle. Once incorporated into DNA, BrdU stays in the cell nuclei essentially permanently. Co-labeling by anti-BrdU antibody with other cell markers such as, e.g., NeuN for mature or doublecortin for immature neurons, enables to detect cells that were born after the BrdU treatment, for example, at precise time moments in the adult life. 2. Cyclin D2 in control over the cell proliferation Cyclins D are cell cycle regulatory proteins that control specific cyclin-dependent kinases. Three cyclins D have been described, namely, D1, D2, and D3. In most of the cells, there is an overlapping expression
Corresponding authors. E-mail addresses: rfi[email protected] (R.K. Filipkowski), [email protected] (L. Kaczmarek).
http://dx.doi.org/10.1016/j.pnpbp.2017.03.028 Received 22 February 2017; Received in revised form 25 March 2017; Accepted 30 March 2017 0278-5846/ © 2017 Elsevier Inc. All rights reserved.
Please cite this article as: Filipkowski, R.K., Progress in Neuropsychopharmacology & Biological Psychiatry (2017), http://dx.doi.org/10.1016/j.pnpbp.2017.03.028
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transplantation and neurogenesis rescue. It was shown recently that wild-type progenitor cells transplanted into DG of cyclin D2 KO mice survived longer when animals were exposed to in an enriched environment (Jamal et al., 2015).
of more than one cyclin D. In such cases, specific ablation of one of them does not reveal any phenotype, apparently because of the compensatory effects exerted by other members of the family. However, in those instances where only one cyclin D is expressed, its deficit produces significant phenotypic defects. For instance, mice lacking cyclin D1 were originally reported to display narrow, tissuespecific abnormalities within the retina and mammary glands (Fantl et al., 1995; Ma et al., 1998; Sicinski et al., 1995). In contrast, mice lacking cyclin D2 displayed abnormalities in the ovaries and testes, as well as in the B-lymphocytes and pancreatic β-cells proliferation as well as cerebellar development (Huard et al., 1999; Robker and Richards, 1998; Sicinski et al., 1996; Solvason et al., 2000). Finally, cyclin D3–deficient mice also showed a narrow, cell-type specific deficits in the development of T-lymphocytes (Sicinska et al., 2003). Neurospheres are believed to be in vitro expandable progeny of neuronal precursors (Reynolds and Weiss, 1992). We have found that cyclin D2 was the only cyclin D that was expressed in the neurospheres during proliferation of the neuronal precursor derived from wild-type adult hippocampal progenitors. In contrast, the hippocampal neurospheres derived from wild-type 5-days old pups, characterized by a robust developmental proliferation of DG neuronal precursors, expressed all three cyclins D (Kowalczyk et al., 2004). Therefore, it was expected that adult functions of the cyclin D2 in the brain could not be compensated after the protein was ablated. In agreement with the aforementioned findings we have discovered that cell cycle of the adult brain neuronal precursors in the cyclin D2 KO mice was greatly impaired. These mice missed almost entirely adult brain neurogenesis in SGZ, as demonstrated by very limited BrdU labeling in this brain region (Garthe et al., 2014; Jedynak et al., 2012; Jedynak et al., 2014) and virtual lack of co-localization with such neuronal markers as NeuN (for mature neurons, studied at three weeks after BrdU injections) as well as Tuj-1 and doublecortin (both markers for immature neurons, investigated 3 days after BrdU treatment) (Jaholkowski et al., 2009; Kondratiuk et al., 2015; Kowalczyk et al., 2004). Detailed time-course of this phenomenon showed that the number of proliferating cells in the SGZ declined dramatically starting from postnatal day 28 (Ansorg et al., 2012). Specific role of cyclin D2 in SGZ neurogenesis was also noted by Matsumoto et al. (2011). Similarly, lack of cyclin D2 markedly impaired labeling of the olfactory bulb at the late time point after the BrdU treatment, indicating impaired neurogenesis in the SVZ (Kowalczyk et al., 2004). Also, neurogenesis within the ciliary margin zone of the retina was recently shown to be diminished in cyclin D2 KO mice (Marcucci et al., 2016). Notably, the neurogenesis deficiency in cD2 KO mice does not concern cells outside the central nervous system, for example, in the nasal neuroepithelium (Kowalczyk et al., 2004). We have also attempted to enhance neurogenesis with treatments known to potentiate it, such as animal exploration of a novel, enriched environment (Kempermann et al., 1997; Rosenzweig and Bennett, 1996; van Praag et al., 2000). Whereas indeed we have observed the increase in BrdU labeling of DG neurons in wild-type controls, no such increase in the number of scarce BrdU-positive cells in the hippocampi of cyclin D2 KO animals could be demonstrated (Kowalczyk et al., 2004). On the other hand, slight increase in the number of both BrdUand doublecortin-positive cells was observed in the DG of cyclin D2 KO mice after kainate intra-amygdala injection, a treatment known to evoke status epilepticus and subsequent development of epilepsy (Kondratiuk et al., 2015). Nevertheless, this number was still manyfold lower than in the wild-type mice. It is of note that cyclin D2 is among a few candidate molecular switches which may control the process of adult brain neurogenesis itself as well as/or the transition from developmental to adult neurogenesis. It is often listed with other molecules whose lack causes almost complete block of adult neurogenesis, especially Tlx and Ascl1 (Andersen et al., 2014; Filipkowski et al., 2005; Urban and Guillemot, 2014). Cyclin D2 KO mice are also being used as a model for cell
3. Structural consequences of deleting cyclin D2 in mice The cyclin D2 mutant mice are ca. 10% smaller than their wild type littermates and their brains are smaller by about 25%. As the overall brain structure appears to be normal, several brain regions, especially cortical ones, including the hippocampus and olfactory bulb in particular are significantly smaller in mutants than in the wild-types (Kowalczyk et al., 2004). Therefore, it appears that cyclin D2 contributes to the developmental neurogenesis, and when the protein is missing, this contribution can be only partially compensated (see e.g., Mirzaa et al., 2014). The specific role of cyclin D2 in cortical developmental neurogenesis was elaborated (Tsunekawa et al., 2012; Tsunekawa and Osumi, 2012). Similarly, Huard et al. (1999) noted cerebellar developmental abnormalities in the cyclin D2 KO mice while Leto et al. (2011) demonstrated critical role of cyclin D2 in the genesis of the cerebellar interneurons. 4. Functional deficits resulting from missing cyclin D2 An interesting phenotype observed in the cyclin D2 KO mice concerns species-typical behaviors that were shown to be hippocampus dependent (Antonawich et al., 1997; Deacon et al., 2002a; Deacon et al., 2002b; Glickman et al., 1970; Kim, 1960; Kimble et al., 1967). These behaviors include: nest construction (Kalueff et al., 2006), digging (Deacon and Rawlins, 2005), and marble burying (Deacon, 2006). Cyclin D2 KO mice showed significant impairment in all of these behaviors (Jedynak et al., 2012). Firstly, cyclin D2 KO mice were building none or poorer nests than control animals. Secondly, these mice were digging less vigorously than control animals. Thirdly, the animals were burying fewer marbles than controls. Moreover, cyclin D2 KO mice were also more active in the open field and automated motility chamber, as well as showed increased explorative behavior in IntelliCages. Both increased motility and explorative behaviors were previously observed in animals with hippocampal lesions. In aggregate, it might be suggested that all of those behavioral deficits could be explained by smaller hippocampi, and not by impaired adult brain neurogenesis (Jedynak et al., 2012). Another phenotype clearly observed in cyclin D2 KO mice is impoverished olfactory function, as shown by inability to detect attractively smelling food, hidden beneath the surface of the cage bedding (Jaholkowski et al., 2009). In this case, it is difficult to conclude whether greatly limited supply of new neurons into the adult olfactory bulb or, alternatively, very profound structural deficiency of the olfactory bulb (Kowalczyk et al., 2004) that might be developmentdependent, is responsible for the phenotype. Probably, the most pronounced functional deficit resulting from deprived neurogenesis in the adult brain of the cyclin D2 KO mice has been described by Walzlein et al. (2008) who studied neural precursor cells that are antitumorigenic in mice, as they can migrate to glioblastomas to induce tumor cell death. The authors reported in adult cyclin D2 KO mice, a reduced supply of neural precursor cells to glioblastomas and the generation of larger tumors compared with wildtype mice. 5. Missing neurogenesis and cyclin D2 KO mouse cognitive behaviors Participation of the hippocampal formation in learning and memory has been well recognized, especially in the formation of spatial cognitive maps and in declarative memory (Davachi, 2006; Eichenbaum, 2006; Moscovitch et al., 2006; Moscovitch et al., 2005; 2
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(McEwen et al., 2012), and leads to a significant decrease of adult neurogenesis (for review see Warner-Schmidt and Duman, 2006), suggestive of a role of this decrease in the development of depression symptoms. Already early studies on neurogenesis demonstrated that chronic antidepressant treatment increased neurogenesis in adult rat hippocampus (Malberg et al., 2000). Therefore, hippocampal neurogenesis has been proposed to underlie therapeutic efficacy of chronic antidepressants treatment (Santarelli et al., 2003). This hypothesis goes along the fact that recovery from depression requires several weeks, the timescale that is paralleled with the time needed for differentiation and incorporation of newborn neurons into existing neuronal hippocampal networks (Balu and Lucki, 2009; Sahay and Hen, 2007). It should, however, be also noted that this notion remains controversial, as other studies showed none or only partial effect of reducing neurogenesis on restoration of behavioral homeostasis by antidepressants (Bessa et al., 2009; David et al., 2007; David et al., 2009; Holick et al., 2008; Meshi et al., 2006; Nollet et al., 2012; Singer et al., 2009; Surget et al., 2008). In fact, a concept of neurogenesis-dependent and -independent mechanisms of antidepressant action was introduced (David et al., 2009). In the cyclin D2 KO mice, we have found that chronic antidepressant treatment with fluoxetine eliminated depression-like behaviors (measured by immobility in the forced swim and tail suspension tests) evoked by exposure to an unpredictable chronic mild stress (Jedynak et al., 2014). In this respect, the mutants did not differ from the wild type controls. Furthermore, we demonstrated lack of impact of the chronic fluoxetine on adult hippocampal neurogenesis in these mice (Jedynak et al., 2014). Therefore, our results suggest that new neurons are not indispensable for the action of such antidepressants as fluoxetine.
Scoville and Milner, 1957; Squire, 1982). Since DG, which is a part of hippocampal formation, is the location where new neurons appear, an obvious hypothesis has been put forward that adult hippocampal neurogenesis is involved in behavioral memory paradigms dependent on the hippocampus (Barnea and Nottebohm, 1994; Gould et al., 1999; Gross, 2000; Kempermann, 2002). Indeed, impaired hippocampal learning and memory were reported in a number of behavioral models, both in rats and mice after use of X-ray irradiation and drugs that inhibit cell division, as well as following gene ablation approaches, the treatments that all negatively affect the neurogenesis, although they are not devoid of major side effects (summarized in Jaholkowski et al., 2009). Subjecting the cyclin D2 KO mice to the same as above, and other behavioral paradigms, assessing hippocampal learning memory has, however, failed to reveal significant impairments (Jaholkowski et al., 2009; Jedynak et al., 2012). In particular, cyclin D2 KO mice showed proper procedural learning, as well as learning in context- (including remote, 36-day memory), cue-, and trace-fear conditioning, Morris water maze, novel object recognition test, and in a multifunctional behavioral system — IntelliCages. Cyclin D2 KO mice also demonstrated correct reversal learning (Jaholkowski et al., 2009). Similarly, Urbach et al. (2013) demonstrated that cyclin D2 KO mutant mice exhibited several indicators of learning Barnes maze during 6 days of training. Therefore, we conclude that our results suggest that adult brain neurogenesis is not obligatory in learning, including the kinds of learning where the role of adult neurogenesis has previously been strongly suggested. More recently, the phenomenon of pattern separation has been suggested to rely on the adult brain neurogenesis. This neurocomputational term describes the processes occurring in the hippocampal formation, enabling the exchange of sets of similar, overlapping information inputs into separate sets of orthogonalized information outputs (Sahay et al., 2011). It is regarded as a key feature of the ability to distinguish between similar places/situations/contexts/events, i.e., context discrimination, and was named the resolution of the memory (Aimone et al., 2011). In fact, animals with experimentally reduced level of neurogenesis recognize (differentiate) the contexts worse than control subjects (Scobie et al., 2009; Tronel et al., 2012). Also, the role of adult neurogenesis in acquisition of spatial version of Morris water maze, particularly with a goal reversal protocol, was postulated to require pattern separation function (Garthe et al., 2009). On this background, Garthe et al. (2014) demonstrated that in the cyclin D2 KO mice hippocampus-dependent learning in the Morris water maze was not generally impaired by the mutation, but specifically functional aspects relying on precise and flexible encoding were affected (Garthe et al., 2014), and these might depend on aforementioned pattern separation (also discussed in Frankland, 2013, a commentary to our Urbach et al., 2013, publication). Ben Abdallah et al. (2013) also showed that cyclin D2 KO mice demonstrated intact spatial learning and memory retention, assessed 24 h following acquisition of the in the Morris water maze. However, cyclin D2 KO mice displayed slight memory deficits one week after acquisition, when compared to the wild types. This difference between KO and control mice was no longer detectable, when animals were tested at 2 and 3 weeks after the training (Ben Abdallah et al., 2013). In aggregate, one may postulate that cyclin D2 KO mice are deficient in a fine tuning of hippocampal function in learning and memory. However, there is an open question whether this deficiency stems from the missing adult brain neurogenesis or is related to the reduced hippocampal size because if its impaired development.
7. Missing neurogenesis and epileptogenesis in cyclin D2 KO mice The term epileptogenesis refers to a latent period of epilepsy development that is considered to involve reorganization of neuronal circuitry. While disturbances and/or increased neurogenesis were observed to accompany epilepsy (Kokaia, 2011; Parent et al., 2006; Parent and Murphy, 2008; Parent et al., 1997; Scharfman et al., 2007; Scharfman and Gray, 2007), the contribution of neurogenesis to epileptogenesis remains controversial. Recent studies have shown that ablating newly generated granule cells produced a significant reduction in seizure frequency, and/or seizure duration in pilocarpine model of status epilepticus (Cho et al., 2015; Hosford et al., 2016). On the other hand, in our study (Kondratiuk et al., 2015), we have investigated epileptogenesis in cyclin D2 KO mice following intra-amygdala injection of kainic acid resulting in status epilepticus. To evaluate the impact of missing neurogenesis on epileptogenesis and early epilepsy, we performed video-EEG monitoring of control and cyclin D2 KO mice for over two weeks following status epilepticus. No differences were observed in: the number of animals with seizures, latency to the first spontaneous seizure, seizure frequency, and seizure duration. Our results indicate that status epilepticus-induced epileptogenesis is not disrupted in cD2 KO mice with markedly reduced adult neurogenesis and that adult brain neurogenesis is not mandatory for status epilepticusinduced epileptogenesis and early epilepsy. 8. Missing neurogenesis and addiction A role of adult brain neurogenesis in ethanol self-administration has been poorly studied, while the negative effects of ethanol consumption and administration on brain neurogenesis have been extensively documented in animals (Crews et al., 2006; Nixon, 2006). Also, cyclin D2 encoding gene was associated with ethanol preference (Mulligan et al., 2006). Therefore, we have verified (Jaholkowski et al., 2011), whether adult hippocampal deficiency observed in cyclin D2 KO mice alters their preference for ethanol. The intake of and preference for ethanol solutions was assessed in two-bottle choice test. Mutant mice
6. Missing neurogenesis and depression Major depression is a common mental disorder, with poorly understood pathophysiology, although stress has been considered as the main cause of depression. Stress most severely affects hippocampal formation 3
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Balu, D.T., Lucki, I., 2009. Adult hippocampal neurogenesis: regulation, functional implications, and contribution to disease pathology. Neurosci. Biobehav. Rev. 33, 232–252. Barnea, A., Nottebohm, F., 1994. Seasonal recruitment of hippocampal neurons in adult free-ranging black-capped chickadees. Proc. Natl. Acad. Sci. U. S. A. 91, 11217–11221. Ben Abdallah, N.M., Filipkowski, R.K., Pruschy, M., Jaholkowski, P., Winkler, J., Kaczmarek, L., et al., 2013. Impaired long-term memory retention: common denominator for acutely or genetically reduced hippocampal neurogenesis in adult mice. Behav. Brain Res. 252, 275–286. Bergmann, O., Spalding, K.L., Frisen, J., 2015. Adult neurogenesis in humans. Cold Spring Harb. Perspect. Biol. 7, a018994. Bessa, J.M., Ferreira, D., Melo, I., Marques, F., Cerqueira, J.J., Palha, J.A., et al., 2009. The mood-improving actions of antidepressants do not depend on neurogenesis but are associated with neuronal remodeling. Mol. Psychiatry 14 (764-73), 39. Cho, K.O., Lybrand, Z.R., Ito, N., Brulet, R., Tafacory, F., Zhang, L., et al., 2015. Aberrant hippocampal neurogenesis contributes to epilepsy and associated cognitive decline. Nat. Commun. 6, 6606. Crews, F.T., Mdzinarishvili, A., Kim, D., He, J., Nixon, K., 2006. Neurogenesis in adolescent brain is potently inhibited by ethanol. Neuroscience 137, 437–445. Davachi, L., 2006. Item, context and relational episodic encoding in humans. Curr. Opin. Neurobiol. 16, 693–700. David, D.J., Klemenhagen, K.C., Holick, K.A., Saxe, M.D., Mendez, I., Santarelli, L., et al., 2007. Efficacy of the MCHR1 antagonist N-[3-(1-{[4-(3,4-difluorophenoxy)phenyl] methyl}(4-piperidyl))-4-methylphenyl]-2-m ethylpropanamide (SNAP 94847) in mouse models of anxiety and depression following acute and chronic administration is independent of hippocampal neurogenesis. J. Pharmacol. Exp. Ther. 321, 237–248. David, D.J., Samuels, B.A., Rainer, Q., Wang, J.W., Marsteller, D., Mendez, I., et al., 2009. Neurogenesis-dependent and -independent effects of fluoxetine in an animal model of anxiety/depression. Neuron 62, 479–493. Deacon, R.M., 2006. Digging and marble burying in mice: simple methods for in vivo identification of biological impacts. Nat. Protoc. 1, 122–124. Deacon, R.M., Bannerman, D.M., Kirby, B.P., Croucher, A., Rawlins, J.N., 2002a. Effects of cytotoxic hippocampal lesions in mice on a cognitive test battery. Behav. Brain Res. 133, 57–68. Deacon, R.M., Croucher, A., Rawlins, J.N., 2002b. Hippocampal cytotoxic lesion effects on species-typical behaviours in mice. Behav. Brain Res. 132, 203–213. Deacon, R.M., Rawlins, J.N., 2005. Hippocampal lesions, species-typical behaviours and anxiety in mice. Behav. Brain Res. 156, 241–249. Eichenbaum, H., 2006. Remembering: functional organization of the declarative memory system. Curr. Biol. 16, R643–R645. Eriksson, P.S., Perfilieva, E., Bjork-Eriksson, T., Alborn, A.M., Nordborg, C., Peterson, D.A., et al., 1998. Neurogenesis in the adult human hippocampus. Nat. Med. 4, 1313–1317. Fantl, V., Stamp, G., Andrews, A., Rosewell, I., Dickson, C., 1995. Mice lacking cyclin D1 are small and show defects in eye and mammary gland development. Genes Dev. 9, 2364–2372. Filipkowski, R.K., Kiryk, A., Kowalczyk, A., Kaczmarek, L., 2005. Genetic models to study adult neurogenesis. Acta Biochim. Pol. 52, 359–372. Frankland, P.W., 2013. Neurogenic evangelism: comment on Urbach et al. (2013). Behav. Neurosci. 127, 126–129. Garthe, A., Behr, J., Kempermann, G., 2009. Adult-generated hippocampal neurons allow the flexible use of spatially precise learning strategies. PLoS One 4, e5464. Garthe, A., Huang, Z., Kaczmarek, L., Filipkowski, R.K., Kempermann, G., 2014. Not all water mazes are created equal: cyclin D2 knockout mice with constitutively suppressed adult hippocampal neurogenesis do show specific spatial learning deficits. Genes Brain Behav. Glickman, S.E., Higgins, T.J., Isaacson, R.L., 1970. Some effects of hippocampal lesions on the behavior of Mongolian gerbils. Physiol. Behav. 5, 931–938. Gould, E., Tanapat, P., Hastings, N.B., Shors, T.J., 1999. Neurogenesis in adulthood: a possible role in learning. Trends Cogn. Sci. 3, 186–192. Gross, C.G., 2000. Neurogenesis in the adult brain: death of a dogma. Nat. Rev. Neurosci. 1, 67–73. Holick, K.A., Lee, D.C., Hen, R., Dulawa, S.C., 2008. Behavioral effects of chronic fluoxetine in BALB/cJ mice do not require adult hippocampal neurogenesis or the serotonin 1A receptor. Neuropsychopharmacology 33, 406–417. Hosford, B.E., Liska, J.P., Danzer, S.C., 2016. Ablation of newly generated hippocampal granule cells has disease-modifying effects in epilepsy. J. Neurosci. 36, 11013–11023. Huard, J.M., Forster, C.C., Carter, M.L., Sicinski, P., Ross, M.E., 1999. Cerebellar histogenesis is disturbed in mice lacking cyclin D2. Development 126, 1927–1935. Jaholkowski, P., Kiryk, A., Jedynak, P., Ben Abdallah, N.M., Knapska, E., Kowalczyk, A., et al., 2009. New hippocampal neurons are not obligatory for memory formation; cyclin D2 knockout mice with no adult brain neurogenesis show learning. Learn. Mem. 16, 439–451. Jaholkowski, P., Mierzejewski, P., Zatorski, P., Scinska, A., Sienkiewicz-Jarosz, H., Kaczmarek, L., et al., 2011. Increased ethanol intake and preference in cyclin D2 knockout mice. Genes Brain Behav. 10, 551–556. Jamal, A.L., Walker, T.L., Waber Nguyen, A.J., Berman, R.F., Kempermann, G., Waldau, B., 2015. Transplanted dentate progenitor cells show increased survival in an enriched environment but do not exert a neurotrophic effect on spatial memory within 2 weeks of engraftment. Cell Transplant 24, 2435–2448. Jedynak, P., Jaholkowski, P., Wozniak, G., Sandi, C., Kaczmarek, L., Filipkowski, R.K., 2012. Lack of cyclin D2 impairing adult brain neurogenesis alters hippocampaldependent behavioral tasks without reducing learning ability. Behav. Brain Res. 227, 159–166. Jedynak, P., Kos, T., Sandi, C., Kaczmarek, L., Filipkowski, R.K., 2014. Mice with ablated
consumed significantly more ethanol than wild-type controls and showed significantly higher preference for ethanol, especially in higher concentrations. We concluded that cyclin D2 might be involved in central regulation of ethanol intake in mice, however, it remains unclear whether this effect is mediated via neurogenesis. 9. Concluding remarks Adult brain neurogenesis is a very interesting phenomenon revealing neuronal stem cells in the adult brain. A great number of studies over the last 20 years have aimed to decipher the role of the phenomenon in brain function and dysfunction, including psychiatric conditions, especially major depressive disorder. Despite all these massive efforts to reveal the role of adult-born neurons in the brain, their function still remains elusive. Cyclin D2 KO mice provide apparently the most striking genetic model of very severely impaired adult brain neurogenesis. Furthermore, the other anti-proliferative treatments employed to affect the neurogenesis in adults, such as cytostatic agents or high doses of irradiation, suffer from significant side effects. Therefore, cyclin D2 KO mice stand out as particularly suitable tool to address the questions about physiological and pathological functions of the adult brain neurogenesis. Admittedly, cyclin D2 KO mice suffer from slight developmental brain structure and size deficits, and possibly unknown (if existing at all) compensatory processes. Incidentally, the very fact that missing cyclin D2 virtually abolished adult neurogenesis with very limited effect on the brain development is very important by itself, as it demonstrates that molecular mechanisms of proliferation of neuronal precursors during development are different from the one operating in the adulthood. With so many functions ascribed to the adult brain neurogenesis it comes as a great surprise how limited are phenotypic disturbances observed in the cyclin D2 KO mice, missing the neurogenesis almost entirely, both under basal, naive conditions as well as after treatments known to enhance the production of the neurons in the adult brain. In fact, all the phenotype features of the cyclin D2 KO mice (except for the anti-glioblastoma response) can be explained by those limited brain abnormalities (without referring to a possible role of the adult neurogenesis). Two possible explanations for these findings should be deliberated in a first place. Either there are hitherto uncovered compensatory mechanisms replacing functions of the newly born neurons or the role of the adult brain neurogenesis has been greatly exaggerated. Acknowledgements This work was supported by National Science Centre, Poland, grant no. 2014/14/M/NZ4/00561 (for RKF). It describes findings partly supported by European Union structural funds – Innovative Economy Operational Program – Project No. POIG.01.01.02-00-109/09 (for LK). References Aimone, J.B., Deng, W., Gage, F.H., 2011. Resolving new memories: a critical look at the dentate gyrus, adult neurogenesis, and pattern separation. Neuron 70, 589–596. Altman, J., Das, G.D., 1965. Autoradiographic and histological evidence of postnatal hippocampal neurogenesis in rats. J. Comp. Neurol. 124, 319–335. Altman, J., Das, G.D., 1966. Autoradiographic and histological studies of postnatal neurogenesis. I. A longitudinal investigation of the kinetics, migration and transformation of cells incorporating tritiated thymidine in neonate rats, with special reference to postnatal neurogenesis in some brain regions. J. Comp. Neurol. 126, 337–389. Andersen, J., Urban, N., Achimastou, A., Ito, A., Simic, M., Ullom, K., et al., 2014. A transcriptional mechanism integrating inputs from extracellular signals to activate hippocampal stem cells. Neuron 83, 1085–1097. Ansorg, A., Witte, O.W., Urbach, A., 2012. Age-dependent kinetics of dentate gyrus neurogenesis in the absence of cyclin D2. BMC Neurosci. 13, 46. Antonawich, F.J., Melton, C.S., Wu, P., Davis, J.N., 1997. Nesting and shredding behavior as an indicator of hippocampal ischemic damage. Brain Res. 764, 249–252.
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Parent, J.M., Yu, T.W., Leibowitz, R.T., Geschwind, D.H., Sloviter, R.S., Lowenstein, D.H., 1997. Dentate granule cell neurogenesis is increased by seizures and contributes to aberrant network reorganization in the adult rat hippocampus. J. Neurosci. 17, 3727–3738. Reynolds, B.A., Weiss, S., 1992. Generation of neurons and astrocytes from isolated cells of the adult mammalian central nervous system. Science 255, 1707–1710. Robker, R.L., Richards, J.S., 1998. Hormone-induced proliferation and differentiation of granulosa cells: a coordinated balance of the cell cycle regulators cyclin D2 and p27Kip1. Mol. Endocrinol. 12, 924–940. Rosenzweig, M.R., Bennett, E.L., 1996. Psychobiology of plasticity: effects of training and experience on brain and behavior. Behav. Brain Res. 78, 57–65. Sahay, A., Hen, R., 2007. Adult hippocampal neurogenesis in depression. Nat. Neurosci. 10, 1110–1115. Sahay, A., Wilson, D.A., Hen, R., 2011. Pattern separation: a common function for new neurons in hippocampus and olfactory bulb. Neuron 70, 582–588. Santarelli, L., Saxe, M., Gross, C., Surget, A., Battaglia, F., Dulawa, S., et al., 2003. Requirement of hippocampal neurogenesis for the behavioral effects of antidepressants. Science 301, 805–809. Scharfman, H., Goodman, J., McCloskey, D., 2007. Ectopic granule cells of the rat dentate gyrus. Dev. Neurosci. 29, 14–27. Scharfman, H.E., Gray, W.P., 2007. Relevance of seizure-induced neurogenesis in animal models of epilepsy to the etiology of temporal lobe epilepsy. Epilepsia 48 (Suppl. 2), 33–41. Scobie, K.N., Hall, B.J., Wilke, S.A., Klemenhagen, K.C., Fujii-Kuriyama, Y., Ghosh, A., et al., 2009. Kruppel-like factor 9 is necessary for late-phase neuronal maturation in the developing dentate gyrus and during adult hippocampal neurogenesis. J. Neurosci. 29, 9875–9887. Scoville, W.B., Milner, B., 1957. Loss of recent memory after bilateral hippocampal lesions. J. Neurol. Neurosurg. Psychiatry 20, 11–21. Sicinska, E., Aifantis, I., Le Cam, L., Swat, W., Borowski, C., Yu, Q., et al., 2003. Requirement for cyclin D3 in lymphocyte development and T cell leukemias. Cancer Cell 4, 451–461. Sicinski, P., Donaher, J.L., Geng, Y., Parker, S.B., Gardner, H., Park, M.Y., et al., 1996. Cyclin D2 is an FSH-responsive gene involved in gonadal cell proliferation and oncogenesis. Nature 384, 470–474. Sicinski, P., Donaher, J.L., Parker, S.B., Li, T., Fazeli, A., Gardner, H., et al., 1995. Cyclin D1 provides a link between development and oncogenesis in the retina and breast. Cell. 82, 621–630. Singer, B.H., Jutkiewicz, E.M., Fuller, C.L., Lichtenwalner, R.J., Zhang, H., Velander, A.J., et al., 2009. Conditional ablation and recovery of forebrain neurogenesis in the mouse. J. Comp. Neurol. 514, 567–582. Smart, I., 1961. Subependymal layer of mouse brain and its cell production as shown by radioautography after thymidine-H3 injection. J. Comp. Neurol. 116, 325. Solvason, N., Wu, W.W., Parry, D., Mahony, D., Lam, E.W., Glassford, J., et al., 2000. Cyclin D2 is essential for BCR-mediated proliferation and CD5 B cell development. Int. Immunol. 12, 631–638. Squire, L.R., 1982. The neuropsychology of human memory. Annu. Rev. Neurosci. 5, 241–273. Surget, A., Saxe, M., Leman, S., Ibarguen-Vargas, Y., Chalon, S., Griebel, G., et al., 2008. Drug-dependent requirement of hippocampal neurogenesis in a model of depression and of antidepressant reversal. Biol Psychiatry 64, 293–301. Tronel, S., Belnoue, L., Grosjean, N., Revest, J.M., Piazza, P.V., Koehl, M., et al., 2012. Adult-born neurons are necessary for extended contextual discrimination. Hippocampus 22, 292–298. Tsunekawa, Y., Britto, J.M., Takahashi, M., Polleux, F., Tan, S.S., Osumi, N., 2012. Cyclin D2 in the basal process of neural progenitors is linked to non-equivalent cell fates. EMBO J. 31, 1879–1892. Tsunekawa, Y., Osumi, N., 2012. How to keep proliferative neural stem/progenitor cells: a critical role of asymmetric inheritance of cyclin D2. Cell Cycle 11, 3550–3554. Urbach, A., Robakiewicz, I., Baum, E., Kaczmarek, L., Witte, O.W., Filipkowski, R.K., 2013. Cyclin D2 knockout mice with depleted adult neurogenesis learn Barnes maze task. Behav. Neurosci. 127, 1–8. Urban, N., Guillemot, F., 2014. Neurogenesis in the embryonic and adult brain: same regulators, different roles. Front Cell Neurosci. 8, 396. van Praag, H., Kempermann, G., Gage, F.H., 2000. Neural consequences of environmental enrichment. Nat. Rev. Neurosci. 1, 191–198. Walzlein, J.H., Synowitz, M., Engels, B., Markovic, D.S., Gabrusiewicz, K., Nikolaev, E., et al., 2008. The antitumorigenic response of neural precursors depends on subventricular proliferation and age. Stem Cells 26, 2945–2954. Warner-Schmidt, J.L., Duman, R.S., 2006. Hippocampal neurogenesis: opposing effects of stress and antidepressant treatment. Hippocampus 16, 239–249.
adult brain neurogenesis are not impaired in antidepressant response to chronic fluoxetine. J. Psychiatr. Res. 56, 106–111. Kalueff, A.V., Keisala, T., Minasyan, A., Kuuslahti, M., Miettinen, S., Tuohimaa, P., 2006. Behavioural anomalies in mice evoked by “Tokyo” disruption of the vitamin D receptor gene. Neurosci. Res. 54, 254–260. Kempermann, G., 2002. Why new neurons? Possible functions for adult hippocampal neurogenesis. J. Neurosci. 22, 635–638. Kempermann, G., Kuhn, H.G., Gage, F.H., 1997. More hippocampal neurons in adult mice living in an enriched environment. Nature 386, 493–495. Kim, C., 1960. Nest building, general activity, and salt preference of rats following hippocampal ablation. J. Comp. Physiol. Psychol. 53, 11–16. Kimble, D.P., Rogers, L., Hendrickson, C.W., 1967. Hippocampal lesions disrupt maternal, not sexual, behavior in the albino rat. J. Comp. Physiol. Psychol. 63, 401–407. Kokaia, M., 2011. Seizure-induced neurogenesis in the adult brain. Eur. J. Neurosci. 33, 1133–1138. Kondratiuk, I., Plucinska, G., Miszczuk, D., Wozniak, G., Szydlowska, K., Kaczmarek, L., et al., 2015. Epileptogenesis following kainic acid-induced status epilepticus in cyclin D2 knock-out mice with diminished adult neurogenesis. PLoS One 10, e0128285. Kowalczyk, A., Filipkowski, R.K., Rylski, M., Wilczynski, G.M., Konopacki, F.A., Jaworski, J., et al., 2004. The critical role of cyclin D2 in adult neurogenesis. J. Cell Biol. 167, 209–213. Leto, K., Bartolini, A., Di Gregorio, A., Imperiale, D., De Luca, A., Parmigiani, E., et al., 2011. Modulation of cell-cycle dynamics is required to regulate the number of cerebellar GABAergic interneurons and their rhythm of maturation. Development 138, 3463–3472. Ma, C., Papermaster, D., Cepko, C.L., 1998. A unique pattern of photoreceptor degeneration in cyclin D1 mutant mice. Proc. Natl. Acad. Sci. U. S. A. 95, 9938–9943. Malberg, J.E., Eisch, A.J., Nestler, E.J., Duman, R.S., 2000. Chronic antidepressant treatment increases neurogenesis in adult rat hippocampus. J. Neurosci. 20, 9104–9110. Marcucci, F., Murcia-Belmonte, V., Wang, Q., Coca, Y., Ferreiro-Galve, S., Kuwajima, T., et al., 2016. The ciliary margin zone of the mammalian retina generates retinal ganglion cells. Cell Rep. 17, 3153–3164. Matsumoto, Y., Tsunekawa, Y., Nomura, T., Suto, F., Matsumata, M., Tsuchiya, S., et al., 2011. Differential proliferation rhythm of neural progenitor and oligodendrocyte precursor cells in the young adult hippocampus. PLoS One 6, e27628. McEwen, B.S., Eiland, L., Hunter, R.G., Miller, M.M., 2012. Stress and anxiety: structural plasticity and epigenetic regulation as a consequence of stress. Neuropharmacology 62, 3–12. Meshi, D., Drew, M.R., Saxe, M., Ansorge, M.S., David, D., Santarelli, L., et al., 2006. Hippocampal neurogenesis is not required for behavioral effects of environmental enrichment. Nat. Neurosci. 9, 729–731. Messier, B., Leblond, C.P., 1960. Cell proliferation and migration as revealed by radioautography after injection of thymidine-H3 into male rats and mice. Am. J. Anat. 106, 247–285. Messier, B., Leblond, C.P., Smart, I., 1958. Presence of DNA synthesis and mitosis in the brain of young adult mice. Exp. Cell Res. 14, 224–226. Mirzaa, G.M., Parry, D.A., Fry, A.E., Giamanco, K.A., Schwartzentruber, J., Vanstone, M., et al., 2014. De novo CCND2 mutations leading to stabilization of cyclin D2 cause megalencephaly-polymicrogyria-polydactyly-hydrocephalus syndrome. Nat. Genet. 46, 510–515. Moscovitch, M., Nadel, L., Winocur, G., Gilboa, A., Rosenbaum, R.S., 2006. The cognitive neuroscience of remote episodic, semantic and spatial memory. Curr. Opin. Neurobiol. 16, 179–190. Moscovitch, M., Rosenbaum, R.S., Gilboa, A., Addis, D.R., Westmacott, R., Grady, C., et al., 2005. Functional neuroanatomy of remote episodic, semantic and spatial memory: a unified account based on multiple trace theory. J. Anat. 207, 35–66. Mulligan, M.K., Ponomarev, I., Hitzemann, R.J., Belknap, J.K., Tabakoff, B., Harris, R.A., et al., 2006. Toward understanding the genetics of alcohol drinking through transcriptome meta-analysis. Proc. Natl. Acad. Sci. U. S. A. 103, 6368–6373. Nixon, K., 2006. Alcohol and adult neurogenesis: roles in neurodegeneration and recovery in chronic alcoholism. Hippocampus 16, 287–295. Nollet, M., Gaillard, P., Tanti, A., Girault, V., Belzung, C., Leman, S., 2012. Neurogenesisindependent antidepressant-like effects on behavior and stress axis response of a dual orexin receptor antagonist in a rodent model of depression. Neuropsychopharmacology 37, 2210–2221. Parent, J.M., Elliott, R.C., Pleasure, S.J., Barbaro, N.M., Lowenstein, D.H., 2006. Aberrant seizure-induced neurogenesis in experimental temporal lobe epilepsy. Ann. Neurol. 59, 81–91. Parent, J.M., Murphy, G.G., 2008. Mechanisms and functional significance of aberrant seizure-induced hippocampal neurogenesis. Epilepsia 49 (Suppl. 5), 19–25.
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Severely impaired adult brain neurogenesis in cyclin D2 knock-out mice produces very limited phenotypic changes Robert K. Filipkowskia,⁎, Leszek Kaczmarekb,⁎ a b
Behavior and Metabolism Research Laboratory, Mossakowski Medical Research Centre, Polish Academy of Sciences, Pawinskiego 5 St., 02-106 Warsaw, Poland Laboratory of Neurobiology, Nencki Institute of Experimental Biology, Polish Academy of Sciences, Pasteura 3 St., 02-093 Warsaw, Poland
A B S T R A C T The discovery of new neurons being produced in the brains of adult mammals (adult brain neurogenesis) began a quest to determine the function(s) of these cells. Major hypotheses in the field have assumed that these neurons play pivotal role, in particular, in learning and memory phenomena, mood control, and epileptogenesis. In our studies summarized herein, we used cyclin D2 knockout (KO) mice, as we have shown that cyclin D2 is the key factor in adult brain neurogenesis and thus its lack produces profound impairment of the process. On the other hand, developmental neurogenesis responsible for the brain formation depends only slightly on cyclin D2, as the mutants display minor structural abnormalities, such as smaller hippocampus and more severe disturbances in the structure of the olfactory bulbs. Surprisingly, the studies have revealed that cyclin D2 KO mice did not show major deficits in several behavioral paradigms assessing hippocampal learning and memory. Furthermore, missing adult brain neurogenesis affected neither action of antidepressants, nor epileptogenesis. On the other hand, minor deficits observed in cyclin D2 KO mice in fine tuning of cognitive functions, species-typical behaviors and alcohol consumption might be explained by a reduced hippocampal size and/or other developmentally driven brain impairments observed in these mutant mice. In aggregate, surprisingly, missing almost entirely adult brain neurogenesis produces only very limited behavioral phenotype that could be attributed to the consequences of the development-dependent minor brain abnormalities.
1. The phenomenon of the adult brain neurogenesis The term adult brain neurogenesis refers to generation of new neurons (due to the proliferation of precursor cells and their differentiation) in the brains of adult animals. Adult brain neurogenesis is limited mostly (although not exclusively) to two populations of dividing cells: (i) those in the subventricular zone (SVZ), with their progeny migrating through the rostral migratory stream to the olfactory bulb, and (ii) those in the subgranular zone (SGZ) of the dentate gyrus (DG) of the hippocampus. Those cells mature into olfactory bulb granule cells and DG granule cells, respectively. In mammals, this phenomenon was initially observed several decades ago, mostly in rodents (Altman and Das, 1965; Altman and Das, 1966; Messier and Leblond, 1960; Messier et al., 1958; Smart, 1961), but has gained paramount recognition over the last two decades, since seminal study by Eriksson et al. (1998) performed on human subjects. In human brain, substantial hippocampal neurogenesis is observed with no detectable olfactory bulb neurogenesis, but with continuous addition of new neurons in the striatum (see Bergmann
⁎
et al., 2015, for review). The term neurogenesis encompasses a cascade of phenomena, starting from proliferation of the neuronal precursors, through their migration and differentiation. The most often used approach to measure the phenomenon is immunocytochemical detection of bromodeoxyuridine (BrdU) in the cell nuclei. BrdU given systemically replaces its natural analogue in DNA, thymidine, with its incorporation being the most massive during the S phase (DNA replication) of the cell cycle. Once incorporated into DNA, BrdU stays in the cell nuclei essentially permanently. Co-labeling by anti-BrdU antibody with other cell markers such as, e.g., NeuN for mature or doublecortin for immature neurons, enables to detect cells that were born after the BrdU treatment, for example, at precise time moments in the adult life. 2. Cyclin D2 in control over the cell proliferation Cyclins D are cell cycle regulatory proteins that control specific cyclin-dependent kinases. Three cyclins D have been described, namely, D1, D2, and D3. In most of the cells, there is an overlapping expression
Corresponding authors. E-mail addresses: rfi[email protected] (R.K. Filipkowski), [email protected] (L. Kaczmarek).
http://dx.doi.org/10.1016/j.pnpbp.2017.03.028 Received 22 February 2017; Received in revised form 25 March 2017; Accepted 30 March 2017 0278-5846/ © 2017 Elsevier Inc. All rights reserved.
Please cite this article as: Filipkowski, R.K., Progress in Neuropsychopharmacology & Biological Psychiatry (2017), http://dx.doi.org/10.1016/j.pnpbp.2017.03.028
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transplantation and neurogenesis rescue. It was shown recently that wild-type progenitor cells transplanted into DG of cyclin D2 KO mice survived longer when animals were exposed to in an enriched environment (Jamal et al., 2015).
of more than one cyclin D. In such cases, specific ablation of one of them does not reveal any phenotype, apparently because of the compensatory effects exerted by other members of the family. However, in those instances where only one cyclin D is expressed, its deficit produces significant phenotypic defects. For instance, mice lacking cyclin D1 were originally reported to display narrow, tissuespecific abnormalities within the retina and mammary glands (Fantl et al., 1995; Ma et al., 1998; Sicinski et al., 1995). In contrast, mice lacking cyclin D2 displayed abnormalities in the ovaries and testes, as well as in the B-lymphocytes and pancreatic β-cells proliferation as well as cerebellar development (Huard et al., 1999; Robker and Richards, 1998; Sicinski et al., 1996; Solvason et al., 2000). Finally, cyclin D3–deficient mice also showed a narrow, cell-type specific deficits in the development of T-lymphocytes (Sicinska et al., 2003). Neurospheres are believed to be in vitro expandable progeny of neuronal precursors (Reynolds and Weiss, 1992). We have found that cyclin D2 was the only cyclin D that was expressed in the neurospheres during proliferation of the neuronal precursor derived from wild-type adult hippocampal progenitors. In contrast, the hippocampal neurospheres derived from wild-type 5-days old pups, characterized by a robust developmental proliferation of DG neuronal precursors, expressed all three cyclins D (Kowalczyk et al., 2004). Therefore, it was expected that adult functions of the cyclin D2 in the brain could not be compensated after the protein was ablated. In agreement with the aforementioned findings we have discovered that cell cycle of the adult brain neuronal precursors in the cyclin D2 KO mice was greatly impaired. These mice missed almost entirely adult brain neurogenesis in SGZ, as demonstrated by very limited BrdU labeling in this brain region (Garthe et al., 2014; Jedynak et al., 2012; Jedynak et al., 2014) and virtual lack of co-localization with such neuronal markers as NeuN (for mature neurons, studied at three weeks after BrdU injections) as well as Tuj-1 and doublecortin (both markers for immature neurons, investigated 3 days after BrdU treatment) (Jaholkowski et al., 2009; Kondratiuk et al., 2015; Kowalczyk et al., 2004). Detailed time-course of this phenomenon showed that the number of proliferating cells in the SGZ declined dramatically starting from postnatal day 28 (Ansorg et al., 2012). Specific role of cyclin D2 in SGZ neurogenesis was also noted by Matsumoto et al. (2011). Similarly, lack of cyclin D2 markedly impaired labeling of the olfactory bulb at the late time point after the BrdU treatment, indicating impaired neurogenesis in the SVZ (Kowalczyk et al., 2004). Also, neurogenesis within the ciliary margin zone of the retina was recently shown to be diminished in cyclin D2 KO mice (Marcucci et al., 2016). Notably, the neurogenesis deficiency in cD2 KO mice does not concern cells outside the central nervous system, for example, in the nasal neuroepithelium (Kowalczyk et al., 2004). We have also attempted to enhance neurogenesis with treatments known to potentiate it, such as animal exploration of a novel, enriched environment (Kempermann et al., 1997; Rosenzweig and Bennett, 1996; van Praag et al., 2000). Whereas indeed we have observed the increase in BrdU labeling of DG neurons in wild-type controls, no such increase in the number of scarce BrdU-positive cells in the hippocampi of cyclin D2 KO animals could be demonstrated (Kowalczyk et al., 2004). On the other hand, slight increase in the number of both BrdUand doublecortin-positive cells was observed in the DG of cyclin D2 KO mice after kainate intra-amygdala injection, a treatment known to evoke status epilepticus and subsequent development of epilepsy (Kondratiuk et al., 2015). Nevertheless, this number was still manyfold lower than in the wild-type mice. It is of note that cyclin D2 is among a few candidate molecular switches which may control the process of adult brain neurogenesis itself as well as/or the transition from developmental to adult neurogenesis. It is often listed with other molecules whose lack causes almost complete block of adult neurogenesis, especially Tlx and Ascl1 (Andersen et al., 2014; Filipkowski et al., 2005; Urban and Guillemot, 2014). Cyclin D2 KO mice are also being used as a model for cell
3. Structural consequences of deleting cyclin D2 in mice The cyclin D2 mutant mice are ca. 10% smaller than their wild type littermates and their brains are smaller by about 25%. As the overall brain structure appears to be normal, several brain regions, especially cortical ones, including the hippocampus and olfactory bulb in particular are significantly smaller in mutants than in the wild-types (Kowalczyk et al., 2004). Therefore, it appears that cyclin D2 contributes to the developmental neurogenesis, and when the protein is missing, this contribution can be only partially compensated (see e.g., Mirzaa et al., 2014). The specific role of cyclin D2 in cortical developmental neurogenesis was elaborated (Tsunekawa et al., 2012; Tsunekawa and Osumi, 2012). Similarly, Huard et al. (1999) noted cerebellar developmental abnormalities in the cyclin D2 KO mice while Leto et al. (2011) demonstrated critical role of cyclin D2 in the genesis of the cerebellar interneurons. 4. Functional deficits resulting from missing cyclin D2 An interesting phenotype observed in the cyclin D2 KO mice concerns species-typical behaviors that were shown to be hippocampus dependent (Antonawich et al., 1997; Deacon et al., 2002a; Deacon et al., 2002b; Glickman et al., 1970; Kim, 1960; Kimble et al., 1967). These behaviors include: nest construction (Kalueff et al., 2006), digging (Deacon and Rawlins, 2005), and marble burying (Deacon, 2006). Cyclin D2 KO mice showed significant impairment in all of these behaviors (Jedynak et al., 2012). Firstly, cyclin D2 KO mice were building none or poorer nests than control animals. Secondly, these mice were digging less vigorously than control animals. Thirdly, the animals were burying fewer marbles than controls. Moreover, cyclin D2 KO mice were also more active in the open field and automated motility chamber, as well as showed increased explorative behavior in IntelliCages. Both increased motility and explorative behaviors were previously observed in animals with hippocampal lesions. In aggregate, it might be suggested that all of those behavioral deficits could be explained by smaller hippocampi, and not by impaired adult brain neurogenesis (Jedynak et al., 2012). Another phenotype clearly observed in cyclin D2 KO mice is impoverished olfactory function, as shown by inability to detect attractively smelling food, hidden beneath the surface of the cage bedding (Jaholkowski et al., 2009). In this case, it is difficult to conclude whether greatly limited supply of new neurons into the adult olfactory bulb or, alternatively, very profound structural deficiency of the olfactory bulb (Kowalczyk et al., 2004) that might be developmentdependent, is responsible for the phenotype. Probably, the most pronounced functional deficit resulting from deprived neurogenesis in the adult brain of the cyclin D2 KO mice has been described by Walzlein et al. (2008) who studied neural precursor cells that are antitumorigenic in mice, as they can migrate to glioblastomas to induce tumor cell death. The authors reported in adult cyclin D2 KO mice, a reduced supply of neural precursor cells to glioblastomas and the generation of larger tumors compared with wildtype mice. 5. Missing neurogenesis and cyclin D2 KO mouse cognitive behaviors Participation of the hippocampal formation in learning and memory has been well recognized, especially in the formation of spatial cognitive maps and in declarative memory (Davachi, 2006; Eichenbaum, 2006; Moscovitch et al., 2006; Moscovitch et al., 2005; 2
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(McEwen et al., 2012), and leads to a significant decrease of adult neurogenesis (for review see Warner-Schmidt and Duman, 2006), suggestive of a role of this decrease in the development of depression symptoms. Already early studies on neurogenesis demonstrated that chronic antidepressant treatment increased neurogenesis in adult rat hippocampus (Malberg et al., 2000). Therefore, hippocampal neurogenesis has been proposed to underlie therapeutic efficacy of chronic antidepressants treatment (Santarelli et al., 2003). This hypothesis goes along the fact that recovery from depression requires several weeks, the timescale that is paralleled with the time needed for differentiation and incorporation of newborn neurons into existing neuronal hippocampal networks (Balu and Lucki, 2009; Sahay and Hen, 2007). It should, however, be also noted that this notion remains controversial, as other studies showed none or only partial effect of reducing neurogenesis on restoration of behavioral homeostasis by antidepressants (Bessa et al., 2009; David et al., 2007; David et al., 2009; Holick et al., 2008; Meshi et al., 2006; Nollet et al., 2012; Singer et al., 2009; Surget et al., 2008). In fact, a concept of neurogenesis-dependent and -independent mechanisms of antidepressant action was introduced (David et al., 2009). In the cyclin D2 KO mice, we have found that chronic antidepressant treatment with fluoxetine eliminated depression-like behaviors (measured by immobility in the forced swim and tail suspension tests) evoked by exposure to an unpredictable chronic mild stress (Jedynak et al., 2014). In this respect, the mutants did not differ from the wild type controls. Furthermore, we demonstrated lack of impact of the chronic fluoxetine on adult hippocampal neurogenesis in these mice (Jedynak et al., 2014). Therefore, our results suggest that new neurons are not indispensable for the action of such antidepressants as fluoxetine.
Scoville and Milner, 1957; Squire, 1982). Since DG, which is a part of hippocampal formation, is the location where new neurons appear, an obvious hypothesis has been put forward that adult hippocampal neurogenesis is involved in behavioral memory paradigms dependent on the hippocampus (Barnea and Nottebohm, 1994; Gould et al., 1999; Gross, 2000; Kempermann, 2002). Indeed, impaired hippocampal learning and memory were reported in a number of behavioral models, both in rats and mice after use of X-ray irradiation and drugs that inhibit cell division, as well as following gene ablation approaches, the treatments that all negatively affect the neurogenesis, although they are not devoid of major side effects (summarized in Jaholkowski et al., 2009). Subjecting the cyclin D2 KO mice to the same as above, and other behavioral paradigms, assessing hippocampal learning memory has, however, failed to reveal significant impairments (Jaholkowski et al., 2009; Jedynak et al., 2012). In particular, cyclin D2 KO mice showed proper procedural learning, as well as learning in context- (including remote, 36-day memory), cue-, and trace-fear conditioning, Morris water maze, novel object recognition test, and in a multifunctional behavioral system — IntelliCages. Cyclin D2 KO mice also demonstrated correct reversal learning (Jaholkowski et al., 2009). Similarly, Urbach et al. (2013) demonstrated that cyclin D2 KO mutant mice exhibited several indicators of learning Barnes maze during 6 days of training. Therefore, we conclude that our results suggest that adult brain neurogenesis is not obligatory in learning, including the kinds of learning where the role of adult neurogenesis has previously been strongly suggested. More recently, the phenomenon of pattern separation has been suggested to rely on the adult brain neurogenesis. This neurocomputational term describes the processes occurring in the hippocampal formation, enabling the exchange of sets of similar, overlapping information inputs into separate sets of orthogonalized information outputs (Sahay et al., 2011). It is regarded as a key feature of the ability to distinguish between similar places/situations/contexts/events, i.e., context discrimination, and was named the resolution of the memory (Aimone et al., 2011). In fact, animals with experimentally reduced level of neurogenesis recognize (differentiate) the contexts worse than control subjects (Scobie et al., 2009; Tronel et al., 2012). Also, the role of adult neurogenesis in acquisition of spatial version of Morris water maze, particularly with a goal reversal protocol, was postulated to require pattern separation function (Garthe et al., 2009). On this background, Garthe et al. (2014) demonstrated that in the cyclin D2 KO mice hippocampus-dependent learning in the Morris water maze was not generally impaired by the mutation, but specifically functional aspects relying on precise and flexible encoding were affected (Garthe et al., 2014), and these might depend on aforementioned pattern separation (also discussed in Frankland, 2013, a commentary to our Urbach et al., 2013, publication). Ben Abdallah et al. (2013) also showed that cyclin D2 KO mice demonstrated intact spatial learning and memory retention, assessed 24 h following acquisition of the in the Morris water maze. However, cyclin D2 KO mice displayed slight memory deficits one week after acquisition, when compared to the wild types. This difference between KO and control mice was no longer detectable, when animals were tested at 2 and 3 weeks after the training (Ben Abdallah et al., 2013). In aggregate, one may postulate that cyclin D2 KO mice are deficient in a fine tuning of hippocampal function in learning and memory. However, there is an open question whether this deficiency stems from the missing adult brain neurogenesis or is related to the reduced hippocampal size because if its impaired development.
7. Missing neurogenesis and epileptogenesis in cyclin D2 KO mice The term epileptogenesis refers to a latent period of epilepsy development that is considered to involve reorganization of neuronal circuitry. While disturbances and/or increased neurogenesis were observed to accompany epilepsy (Kokaia, 2011; Parent et al., 2006; Parent and Murphy, 2008; Parent et al., 1997; Scharfman et al., 2007; Scharfman and Gray, 2007), the contribution of neurogenesis to epileptogenesis remains controversial. Recent studies have shown that ablating newly generated granule cells produced a significant reduction in seizure frequency, and/or seizure duration in pilocarpine model of status epilepticus (Cho et al., 2015; Hosford et al., 2016). On the other hand, in our study (Kondratiuk et al., 2015), we have investigated epileptogenesis in cyclin D2 KO mice following intra-amygdala injection of kainic acid resulting in status epilepticus. To evaluate the impact of missing neurogenesis on epileptogenesis and early epilepsy, we performed video-EEG monitoring of control and cyclin D2 KO mice for over two weeks following status epilepticus. No differences were observed in: the number of animals with seizures, latency to the first spontaneous seizure, seizure frequency, and seizure duration. Our results indicate that status epilepticus-induced epileptogenesis is not disrupted in cD2 KO mice with markedly reduced adult neurogenesis and that adult brain neurogenesis is not mandatory for status epilepticusinduced epileptogenesis and early epilepsy. 8. Missing neurogenesis and addiction A role of adult brain neurogenesis in ethanol self-administration has been poorly studied, while the negative effects of ethanol consumption and administration on brain neurogenesis have been extensively documented in animals (Crews et al., 2006; Nixon, 2006). Also, cyclin D2 encoding gene was associated with ethanol preference (Mulligan et al., 2006). Therefore, we have verified (Jaholkowski et al., 2011), whether adult hippocampal deficiency observed in cyclin D2 KO mice alters their preference for ethanol. The intake of and preference for ethanol solutions was assessed in two-bottle choice test. Mutant mice
6. Missing neurogenesis and depression Major depression is a common mental disorder, with poorly understood pathophysiology, although stress has been considered as the main cause of depression. Stress most severely affects hippocampal formation 3
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Balu, D.T., Lucki, I., 2009. Adult hippocampal neurogenesis: regulation, functional implications, and contribution to disease pathology. Neurosci. Biobehav. Rev. 33, 232–252. Barnea, A., Nottebohm, F., 1994. Seasonal recruitment of hippocampal neurons in adult free-ranging black-capped chickadees. Proc. Natl. Acad. Sci. U. S. A. 91, 11217–11221. Ben Abdallah, N.M., Filipkowski, R.K., Pruschy, M., Jaholkowski, P., Winkler, J., Kaczmarek, L., et al., 2013. Impaired long-term memory retention: common denominator for acutely or genetically reduced hippocampal neurogenesis in adult mice. Behav. Brain Res. 252, 275–286. Bergmann, O., Spalding, K.L., Frisen, J., 2015. Adult neurogenesis in humans. Cold Spring Harb. Perspect. Biol. 7, a018994. Bessa, J.M., Ferreira, D., Melo, I., Marques, F., Cerqueira, J.J., Palha, J.A., et al., 2009. The mood-improving actions of antidepressants do not depend on neurogenesis but are associated with neuronal remodeling. Mol. Psychiatry 14 (764-73), 39. Cho, K.O., Lybrand, Z.R., Ito, N., Brulet, R., Tafacory, F., Zhang, L., et al., 2015. Aberrant hippocampal neurogenesis contributes to epilepsy and associated cognitive decline. Nat. Commun. 6, 6606. Crews, F.T., Mdzinarishvili, A., Kim, D., He, J., Nixon, K., 2006. Neurogenesis in adolescent brain is potently inhibited by ethanol. Neuroscience 137, 437–445. Davachi, L., 2006. Item, context and relational episodic encoding in humans. Curr. Opin. Neurobiol. 16, 693–700. David, D.J., Klemenhagen, K.C., Holick, K.A., Saxe, M.D., Mendez, I., Santarelli, L., et al., 2007. Efficacy of the MCHR1 antagonist N-[3-(1-{[4-(3,4-difluorophenoxy)phenyl] methyl}(4-piperidyl))-4-methylphenyl]-2-m ethylpropanamide (SNAP 94847) in mouse models of anxiety and depression following acute and chronic administration is independent of hippocampal neurogenesis. J. Pharmacol. Exp. Ther. 321, 237–248. David, D.J., Samuels, B.A., Rainer, Q., Wang, J.W., Marsteller, D., Mendez, I., et al., 2009. Neurogenesis-dependent and -independent effects of fluoxetine in an animal model of anxiety/depression. Neuron 62, 479–493. Deacon, R.M., 2006. Digging and marble burying in mice: simple methods for in vivo identification of biological impacts. Nat. Protoc. 1, 122–124. Deacon, R.M., Bannerman, D.M., Kirby, B.P., Croucher, A., Rawlins, J.N., 2002a. Effects of cytotoxic hippocampal lesions in mice on a cognitive test battery. Behav. Brain Res. 133, 57–68. Deacon, R.M., Croucher, A., Rawlins, J.N., 2002b. Hippocampal cytotoxic lesion effects on species-typical behaviours in mice. Behav. Brain Res. 132, 203–213. Deacon, R.M., Rawlins, J.N., 2005. Hippocampal lesions, species-typical behaviours and anxiety in mice. Behav. Brain Res. 156, 241–249. Eichenbaum, H., 2006. Remembering: functional organization of the declarative memory system. Curr. Biol. 16, R643–R645. Eriksson, P.S., Perfilieva, E., Bjork-Eriksson, T., Alborn, A.M., Nordborg, C., Peterson, D.A., et al., 1998. Neurogenesis in the adult human hippocampus. Nat. Med. 4, 1313–1317. Fantl, V., Stamp, G., Andrews, A., Rosewell, I., Dickson, C., 1995. Mice lacking cyclin D1 are small and show defects in eye and mammary gland development. Genes Dev. 9, 2364–2372. Filipkowski, R.K., Kiryk, A., Kowalczyk, A., Kaczmarek, L., 2005. Genetic models to study adult neurogenesis. Acta Biochim. Pol. 52, 359–372. Frankland, P.W., 2013. Neurogenic evangelism: comment on Urbach et al. (2013). Behav. Neurosci. 127, 126–129. Garthe, A., Behr, J., Kempermann, G., 2009. Adult-generated hippocampal neurons allow the flexible use of spatially precise learning strategies. PLoS One 4, e5464. Garthe, A., Huang, Z., Kaczmarek, L., Filipkowski, R.K., Kempermann, G., 2014. Not all water mazes are created equal: cyclin D2 knockout mice with constitutively suppressed adult hippocampal neurogenesis do show specific spatial learning deficits. Genes Brain Behav. Glickman, S.E., Higgins, T.J., Isaacson, R.L., 1970. Some effects of hippocampal lesions on the behavior of Mongolian gerbils. Physiol. Behav. 5, 931–938. Gould, E., Tanapat, P., Hastings, N.B., Shors, T.J., 1999. Neurogenesis in adulthood: a possible role in learning. Trends Cogn. Sci. 3, 186–192. Gross, C.G., 2000. Neurogenesis in the adult brain: death of a dogma. Nat. Rev. Neurosci. 1, 67–73. Holick, K.A., Lee, D.C., Hen, R., Dulawa, S.C., 2008. Behavioral effects of chronic fluoxetine in BALB/cJ mice do not require adult hippocampal neurogenesis or the serotonin 1A receptor. Neuropsychopharmacology 33, 406–417. Hosford, B.E., Liska, J.P., Danzer, S.C., 2016. Ablation of newly generated hippocampal granule cells has disease-modifying effects in epilepsy. J. Neurosci. 36, 11013–11023. Huard, J.M., Forster, C.C., Carter, M.L., Sicinski, P., Ross, M.E., 1999. Cerebellar histogenesis is disturbed in mice lacking cyclin D2. Development 126, 1927–1935. Jaholkowski, P., Kiryk, A., Jedynak, P., Ben Abdallah, N.M., Knapska, E., Kowalczyk, A., et al., 2009. New hippocampal neurons are not obligatory for memory formation; cyclin D2 knockout mice with no adult brain neurogenesis show learning. Learn. Mem. 16, 439–451. Jaholkowski, P., Mierzejewski, P., Zatorski, P., Scinska, A., Sienkiewicz-Jarosz, H., Kaczmarek, L., et al., 2011. Increased ethanol intake and preference in cyclin D2 knockout mice. Genes Brain Behav. 10, 551–556. Jamal, A.L., Walker, T.L., Waber Nguyen, A.J., Berman, R.F., Kempermann, G., Waldau, B., 2015. Transplanted dentate progenitor cells show increased survival in an enriched environment but do not exert a neurotrophic effect on spatial memory within 2 weeks of engraftment. Cell Transplant 24, 2435–2448. Jedynak, P., Jaholkowski, P., Wozniak, G., Sandi, C., Kaczmarek, L., Filipkowski, R.K., 2012. Lack of cyclin D2 impairing adult brain neurogenesis alters hippocampaldependent behavioral tasks without reducing learning ability. Behav. Brain Res. 227, 159–166. Jedynak, P., Kos, T., Sandi, C., Kaczmarek, L., Filipkowski, R.K., 2014. Mice with ablated
consumed significantly more ethanol than wild-type controls and showed significantly higher preference for ethanol, especially in higher concentrations. We concluded that cyclin D2 might be involved in central regulation of ethanol intake in mice, however, it remains unclear whether this effect is mediated via neurogenesis. 9. Concluding remarks Adult brain neurogenesis is a very interesting phenomenon revealing neuronal stem cells in the adult brain. A great number of studies over the last 20 years have aimed to decipher the role of the phenomenon in brain function and dysfunction, including psychiatric conditions, especially major depressive disorder. Despite all these massive efforts to reveal the role of adult-born neurons in the brain, their function still remains elusive. Cyclin D2 KO mice provide apparently the most striking genetic model of very severely impaired adult brain neurogenesis. Furthermore, the other anti-proliferative treatments employed to affect the neurogenesis in adults, such as cytostatic agents or high doses of irradiation, suffer from significant side effects. Therefore, cyclin D2 KO mice stand out as particularly suitable tool to address the questions about physiological and pathological functions of the adult brain neurogenesis. Admittedly, cyclin D2 KO mice suffer from slight developmental brain structure and size deficits, and possibly unknown (if existing at all) compensatory processes. Incidentally, the very fact that missing cyclin D2 virtually abolished adult neurogenesis with very limited effect on the brain development is very important by itself, as it demonstrates that molecular mechanisms of proliferation of neuronal precursors during development are different from the one operating in the adulthood. With so many functions ascribed to the adult brain neurogenesis it comes as a great surprise how limited are phenotypic disturbances observed in the cyclin D2 KO mice, missing the neurogenesis almost entirely, both under basal, naive conditions as well as after treatments known to enhance the production of the neurons in the adult brain. In fact, all the phenotype features of the cyclin D2 KO mice (except for the anti-glioblastoma response) can be explained by those limited brain abnormalities (without referring to a possible role of the adult neurogenesis). Two possible explanations for these findings should be deliberated in a first place. Either there are hitherto uncovered compensatory mechanisms replacing functions of the newly born neurons or the role of the adult brain neurogenesis has been greatly exaggerated. Acknowledgements This work was supported by National Science Centre, Poland, grant no. 2014/14/M/NZ4/00561 (for RKF). It describes findings partly supported by European Union structural funds – Innovative Economy Operational Program – Project No. POIG.01.01.02-00-109/09 (for LK). References Aimone, J.B., Deng, W., Gage, F.H., 2011. Resolving new memories: a critical look at the dentate gyrus, adult neurogenesis, and pattern separation. Neuron 70, 589–596. Altman, J., Das, G.D., 1965. Autoradiographic and histological evidence of postnatal hippocampal neurogenesis in rats. J. Comp. Neurol. 124, 319–335. Altman, J., Das, G.D., 1966. Autoradiographic and histological studies of postnatal neurogenesis. I. A longitudinal investigation of the kinetics, migration and transformation of cells incorporating tritiated thymidine in neonate rats, with special reference to postnatal neurogenesis in some brain regions. J. Comp. Neurol. 126, 337–389. Andersen, J., Urban, N., Achimastou, A., Ito, A., Simic, M., Ullom, K., et al., 2014. A transcriptional mechanism integrating inputs from extracellular signals to activate hippocampal stem cells. Neuron 83, 1085–1097. Ansorg, A., Witte, O.W., Urbach, A., 2012. Age-dependent kinetics of dentate gyrus neurogenesis in the absence of cyclin D2. BMC Neurosci. 13, 46. Antonawich, F.J., Melton, C.S., Wu, P., Davis, J.N., 1997. Nesting and shredding behavior as an indicator of hippocampal ischemic damage. Brain Res. 764, 249–252.
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R.K. Filipkowski, L. Kaczmarek
Parent, J.M., Yu, T.W., Leibowitz, R.T., Geschwind, D.H., Sloviter, R.S., Lowenstein, D.H., 1997. Dentate granule cell neurogenesis is increased by seizures and contributes to aberrant network reorganization in the adult rat hippocampus. J. Neurosci. 17, 3727–3738. Reynolds, B.A., Weiss, S., 1992. Generation of neurons and astrocytes from isolated cells of the adult mammalian central nervous system. Science 255, 1707–1710. Robker, R.L., Richards, J.S., 1998. Hormone-induced proliferation and differentiation of granulosa cells: a coordinated balance of the cell cycle regulators cyclin D2 and p27Kip1. Mol. Endocrinol. 12, 924–940. Rosenzweig, M.R., Bennett, E.L., 1996. Psychobiology of plasticity: effects of training and experience on brain and behavior. Behav. Brain Res. 78, 57–65. Sahay, A., Hen, R., 2007. Adult hippocampal neurogenesis in depression. Nat. Neurosci. 10, 1110–1115. Sahay, A., Wilson, D.A., Hen, R., 2011. Pattern separation: a common function for new neurons in hippocampus and olfactory bulb. Neuron 70, 582–588. Santarelli, L., Saxe, M., Gross, C., Surget, A., Battaglia, F., Dulawa, S., et al., 2003. Requirement of hippocampal neurogenesis for the behavioral effects of antidepressants. Science 301, 805–809. Scharfman, H., Goodman, J., McCloskey, D., 2007. Ectopic granule cells of the rat dentate gyrus. Dev. Neurosci. 29, 14–27. Scharfman, H.E., Gray, W.P., 2007. Relevance of seizure-induced neurogenesis in animal models of epilepsy to the etiology of temporal lobe epilepsy. Epilepsia 48 (Suppl. 2), 33–41. Scobie, K.N., Hall, B.J., Wilke, S.A., Klemenhagen, K.C., Fujii-Kuriyama, Y., Ghosh, A., et al., 2009. Kruppel-like factor 9 is necessary for late-phase neuronal maturation in the developing dentate gyrus and during adult hippocampal neurogenesis. J. Neurosci. 29, 9875–9887. Scoville, W.B., Milner, B., 1957. Loss of recent memory after bilateral hippocampal lesions. J. Neurol. Neurosurg. Psychiatry 20, 11–21. Sicinska, E., Aifantis, I., Le Cam, L., Swat, W., Borowski, C., Yu, Q., et al., 2003. Requirement for cyclin D3 in lymphocyte development and T cell leukemias. Cancer Cell 4, 451–461. Sicinski, P., Donaher, J.L., Geng, Y., Parker, S.B., Gardner, H., Park, M.Y., et al., 1996. Cyclin D2 is an FSH-responsive gene involved in gonadal cell proliferation and oncogenesis. Nature 384, 470–474. Sicinski, P., Donaher, J.L., Parker, S.B., Li, T., Fazeli, A., Gardner, H., et al., 1995. Cyclin D1 provides a link between development and oncogenesis in the retina and breast. Cell. 82, 621–630. Singer, B.H., Jutkiewicz, E.M., Fuller, C.L., Lichtenwalner, R.J., Zhang, H., Velander, A.J., et al., 2009. Conditional ablation and recovery of forebrain neurogenesis in the mouse. J. Comp. Neurol. 514, 567–582. Smart, I., 1961. Subependymal layer of mouse brain and its cell production as shown by radioautography after thymidine-H3 injection. J. Comp. Neurol. 116, 325. Solvason, N., Wu, W.W., Parry, D., Mahony, D., Lam, E.W., Glassford, J., et al., 2000. Cyclin D2 is essential for BCR-mediated proliferation and CD5 B cell development. Int. Immunol. 12, 631–638. Squire, L.R., 1982. The neuropsychology of human memory. Annu. Rev. Neurosci. 5, 241–273. Surget, A., Saxe, M., Leman, S., Ibarguen-Vargas, Y., Chalon, S., Griebel, G., et al., 2008. Drug-dependent requirement of hippocampal neurogenesis in a model of depression and of antidepressant reversal. Biol Psychiatry 64, 293–301. Tronel, S., Belnoue, L., Grosjean, N., Revest, J.M., Piazza, P.V., Koehl, M., et al., 2012. Adult-born neurons are necessary for extended contextual discrimination. Hippocampus 22, 292–298. Tsunekawa, Y., Britto, J.M., Takahashi, M., Polleux, F., Tan, S.S., Osumi, N., 2012. Cyclin D2 in the basal process of neural progenitors is linked to non-equivalent cell fates. EMBO J. 31, 1879–1892. Tsunekawa, Y., Osumi, N., 2012. How to keep proliferative neural stem/progenitor cells: a critical role of asymmetric inheritance of cyclin D2. Cell Cycle 11, 3550–3554. Urbach, A., Robakiewicz, I., Baum, E., Kaczmarek, L., Witte, O.W., Filipkowski, R.K., 2013. Cyclin D2 knockout mice with depleted adult neurogenesis learn Barnes maze task. Behav. Neurosci. 127, 1–8. Urban, N., Guillemot, F., 2014. Neurogenesis in the embryonic and adult brain: same regulators, different roles. Front Cell Neurosci. 8, 396. van Praag, H., Kempermann, G., Gage, F.H., 2000. Neural consequences of environmental enrichment. Nat. Rev. Neurosci. 1, 191–198. Walzlein, J.H., Synowitz, M., Engels, B., Markovic, D.S., Gabrusiewicz, K., Nikolaev, E., et al., 2008. The antitumorigenic response of neural precursors depends on subventricular proliferation and age. Stem Cells 26, 2945–2954. Warner-Schmidt, J.L., Duman, R.S., 2006. Hippocampal neurogenesis: opposing effects of stress and antidepressant treatment. Hippocampus 16, 239–249.
adult brain neurogenesis are not impaired in antidepressant response to chronic fluoxetine. J. Psychiatr. Res. 56, 106–111. Kalueff, A.V., Keisala, T., Minasyan, A., Kuuslahti, M., Miettinen, S., Tuohimaa, P., 2006. Behavioural anomalies in mice evoked by “Tokyo” disruption of the vitamin D receptor gene. Neurosci. Res. 54, 254–260. Kempermann, G., 2002. Why new neurons? Possible functions for adult hippocampal neurogenesis. J. Neurosci. 22, 635–638. Kempermann, G., Kuhn, H.G., Gage, F.H., 1997. More hippocampal neurons in adult mice living in an enriched environment. Nature 386, 493–495. Kim, C., 1960. Nest building, general activity, and salt preference of rats following hippocampal ablation. J. Comp. Physiol. Psychol. 53, 11–16. Kimble, D.P., Rogers, L., Hendrickson, C.W., 1967. Hippocampal lesions disrupt maternal, not sexual, behavior in the albino rat. J. Comp. Physiol. Psychol. 63, 401–407. Kokaia, M., 2011. Seizure-induced neurogenesis in the adult brain. Eur. J. Neurosci. 33, 1133–1138. Kondratiuk, I., Plucinska, G., Miszczuk, D., Wozniak, G., Szydlowska, K., Kaczmarek, L., et al., 2015. Epileptogenesis following kainic acid-induced status epilepticus in cyclin D2 knock-out mice with diminished adult neurogenesis. PLoS One 10, e0128285. Kowalczyk, A., Filipkowski, R.K., Rylski, M., Wilczynski, G.M., Konopacki, F.A., Jaworski, J., et al., 2004. The critical role of cyclin D2 in adult neurogenesis. J. Cell Biol. 167, 209–213. Leto, K., Bartolini, A., Di Gregorio, A., Imperiale, D., De Luca, A., Parmigiani, E., et al., 2011. Modulation of cell-cycle dynamics is required to regulate the number of cerebellar GABAergic interneurons and their rhythm of maturation. Development 138, 3463–3472. Ma, C., Papermaster, D., Cepko, C.L., 1998. A unique pattern of photoreceptor degeneration in cyclin D1 mutant mice. Proc. Natl. Acad. Sci. U. S. A. 95, 9938–9943. Malberg, J.E., Eisch, A.J., Nestler, E.J., Duman, R.S., 2000. Chronic antidepressant treatment increases neurogenesis in adult rat hippocampus. J. Neurosci. 20, 9104–9110. Marcucci, F., Murcia-Belmonte, V., Wang, Q., Coca, Y., Ferreiro-Galve, S., Kuwajima, T., et al., 2016. The ciliary margin zone of the mammalian retina generates retinal ganglion cells. Cell Rep. 17, 3153–3164. Matsumoto, Y., Tsunekawa, Y., Nomura, T., Suto, F., Matsumata, M., Tsuchiya, S., et al., 2011. Differential proliferation rhythm of neural progenitor and oligodendrocyte precursor cells in the young adult hippocampus. PLoS One 6, e27628. McEwen, B.S., Eiland, L., Hunter, R.G., Miller, M.M., 2012. Stress and anxiety: structural plasticity and epigenetic regulation as a consequence of stress. Neuropharmacology 62, 3–12. Meshi, D., Drew, M.R., Saxe, M., Ansorge, M.S., David, D., Santarelli, L., et al., 2006. Hippocampal neurogenesis is not required for behavioral effects of environmental enrichment. Nat. Neurosci. 9, 729–731. Messier, B., Leblond, C.P., 1960. Cell proliferation and migration as revealed by radioautography after injection of thymidine-H3 into male rats and mice. Am. J. Anat. 106, 247–285. Messier, B., Leblond, C.P., Smart, I., 1958. Presence of DNA synthesis and mitosis in the brain of young adult mice. Exp. Cell Res. 14, 224–226. Mirzaa, G.M., Parry, D.A., Fry, A.E., Giamanco, K.A., Schwartzentruber, J., Vanstone, M., et al., 2014. De novo CCND2 mutations leading to stabilization of cyclin D2 cause megalencephaly-polymicrogyria-polydactyly-hydrocephalus syndrome. Nat. Genet. 46, 510–515. Moscovitch, M., Nadel, L., Winocur, G., Gilboa, A., Rosenbaum, R.S., 2006. The cognitive neuroscience of remote episodic, semantic and spatial memory. Curr. Opin. Neurobiol. 16, 179–190. Moscovitch, M., Rosenbaum, R.S., Gilboa, A., Addis, D.R., Westmacott, R., Grady, C., et al., 2005. Functional neuroanatomy of remote episodic, semantic and spatial memory: a unified account based on multiple trace theory. J. Anat. 207, 35–66. Mulligan, M.K., Ponomarev, I., Hitzemann, R.J., Belknap, J.K., Tabakoff, B., Harris, R.A., et al., 2006. Toward understanding the genetics of alcohol drinking through transcriptome meta-analysis. Proc. Natl. Acad. Sci. U. S. A. 103, 6368–6373. Nixon, K., 2006. Alcohol and adult neurogenesis: roles in neurodegeneration and recovery in chronic alcoholism. Hippocampus 16, 287–295. Nollet, M., Gaillard, P., Tanti, A., Girault, V., Belzung, C., Leman, S., 2012. Neurogenesisindependent antidepressant-like effects on behavior and stress axis response of a dual orexin receptor antagonist in a rodent model of depression. Neuropsychopharmacology 37, 2210–2221. Parent, J.M., Elliott, R.C., Pleasure, S.J., Barbaro, N.M., Lowenstein, D.H., 2006. Aberrant seizure-induced neurogenesis in experimental temporal lobe epilepsy. Ann. Neurol. 59, 81–91. Parent, J.M., Murphy, G.G., 2008. Mechanisms and functional significance of aberrant seizure-induced hippocampal neurogenesis. Epilepsia 49 (Suppl. 5), 19–25.
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