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Numb promotes both progenitor and neuronal cell fates at distinct stages of retinal development
Poster Session 1 Abstracts 2 June 2008 / Int. J. Devl Neuroscience 26 (2008) 841–866
[P1.22] Numb promotes both progenitor and neuronal cell fates at distinct stages of retinal development A. Kechad 1,3,*, M. Cayouette 2,3 1
IRCM, Canada Universite´ de Montreal, Canada 3 McGill University, Canada *Corresponding author. 2
Introduction: The production of cell diversity in multicellular organisms depends on asymmetric cell divisions, in which the mother cell segregates cell fate determinants asymmetrically into only one of the two daughter cells, thereby instructing different fates. In the developing retina, the cell fate determinant Numb, a Notch signalling inhibitor, is asymmetrically localized in mitotic retinal progenitor cells and, depending on the orientation of cell division, inherited symmetrically or asymmetrically by the daughter cells. The precise role of Numb in vertebrate neural cell fate decisions, however, remains unclear. Conditional inactivation of Numb in the developing mouse cortex suggests that Numb specifies the progenitor cell fate, but since Numb was inactivated from early stages of corticogenesis (E8.5–E10.5), the specific role of Numb at later stages remains unknown. Methods and results: Here we used the mouse retina as a model system to study Numb function at different stages of neural development. We first used the Cre-loxP system to direct restricted in vivo inactivation of Numb in the retina from E10.5. Analysis of adult mutant retinas showed reduced neuronal differentiation, whereas analysis of embryonic mutant retinas showed reduced proliferation. It remained unclear, however, whether reduced neuronal differentiation was indirectly due to decreased proliferation at early stages or whether Numb directly controls neuronal differentiation at late stages. To test this model, we used retroviral vectors expressing Cre recombinase and GFP to infect NumbloxP/loxP mouse retinas at early and late stages of retinal development. Analysis of cell composition and size of each resulting knockout clone showed that early inactivation of Numb significantly reduces clone size, whereas late inactivation of Numb does not affect clone size but drastically decrease non-photoreceptor cell production. Conclusion: These results indicate that Numb promotes the progenitor fate at early stages of development, whereas it promotes the non-photoreceptor cell fate at later stages, suggesting a model in which Numb regulates different types of asymmetric cell divisions (Progenitor + Neuron or Neuron A + Neuron B) at distinct stages of development. doi: 10.1016/j.ijdevneu.2008.09.072 [P1.23] EphrinB3 and its receptor EphA4 control adult subventricular zone neurogenesis J. Ricard *, J. Salinas, D. Liebl University of Miami, USA *Corresponding author. Keywords: Ephrin; Subventricular zone; Neurogenesis
Ephrins and their Eph receptors regulate many developmental events in the central nervous system, and are down-regulated after birth. However, they are still expressed in discrete areas of the post-natal brain, in particular the subventricular zone (SVZ) where olfactory bulb (OB) neurons are continuously generated. Using gene-targeted knockout mice we studied the role of ephrinB3 and
849
its receptor EphA4 on adult neurogenesis. Mice lacking ephrinB3 exhibited increased proliferation in the SVZ and we located this protein just outside of the germinal zone. EphrinB3/ mice were also found to have a higher rate of cell death in the SVZ that may compensate for the increased proliferation. Moreover, ephrinB3 was found to be expressed around the rostral migratory stream and its absence hampered normal neuroblast migration to the OB. One of ephrinB3 receptors, EphA4, was also found to regulate neuroblast migration. These data provide evidence that ephrins and Eph receptors regulate several steps of the neurogenesis process in the subventricular zone of the adult brain. doi: 10.1016/j.ijdevneu.2008.09.073 [P1.24] Effects of inflammatory signaling on the outcome of allogeneic neural stem cell transplantation Z. Chen *, T. Palmer Stanford University, USA *Corresponding author. Keywords: Stem; Transplantation; Hippocampus; Inflammation
Transplantation of neural precursors or neural stem cells derived from ES cells or isolated from fetal and adult tissues is a promising strategy for treating neurological diseases. However, allogeneic and xenogeneic cellular grafts can elicit activation of both the innate and adaptive immune system. Despite the immunological privilege of the central nervous system, the effects of immune recognition on outcome are not fully understood. We have been evaluating immunologically matched and mismatched neural stem cells into different areas of adult mouse brain to determine the influence of immune signaling on the differentiation and survival of transplanted neural progenitors. Different brain areas represent unique niches that instruct the grafted cells towards different fates and we have found that mismatch-induced immune recognition most significantly effects the production of neurons when grafts are placed into neurogenic sites such as the hippocampus. Ongoing work examines interventions that may enhance neurogenesis and transplant efficacy. doi: 10.1016/j.ijdevneu.2008.09.074 [P1.25] Loss of the transcription factor TLX in dorsal progenitor cells leads to decreased cortical size and reduced anxiety E. Drill 1,*, E. Thiels 1, E.F. Greiner 2, G. Schutz 2, A.P. Monaghan 1 1
University of Pittsburgh, USA German Cancer Research Center, Germany *Corresponding author. 2
Keywords: Tailless; Cortex; Behavior; Conditional mutant
TLX (Nr2e1) is a transcription factor expressed in neural progenitor cells (PCs) throughout development and in regions of adult neurogenesis. TLX regulates proliferation in both embryonic and adult PCs. Loss of TLX leads to reductions in the adult in both the surface area and the thickness of the cerebral cortex, as well as reductions in other forebrain-derived structures including the dentate gyrus, the entorhinal cortex, the amygdala, and the striatum. These animals exhibit distinct behavioral abnormalities, including severe aggression, reduced anxiety, and late-onset epilepsy. These defects are associated with changes in both dorsal and ventral PCs. In
[P1.22] Numb promotes both progenitor and neuronal cell fates at distinct stages of retinal development A. Kechad 1,3,*, M. Cayouette 2,3 1
IRCM, Canada Universite´ de Montreal, Canada 3 McGill University, Canada *Corresponding author. 2
Introduction: The production of cell diversity in multicellular organisms depends on asymmetric cell divisions, in which the mother cell segregates cell fate determinants asymmetrically into only one of the two daughter cells, thereby instructing different fates. In the developing retina, the cell fate determinant Numb, a Notch signalling inhibitor, is asymmetrically localized in mitotic retinal progenitor cells and, depending on the orientation of cell division, inherited symmetrically or asymmetrically by the daughter cells. The precise role of Numb in vertebrate neural cell fate decisions, however, remains unclear. Conditional inactivation of Numb in the developing mouse cortex suggests that Numb specifies the progenitor cell fate, but since Numb was inactivated from early stages of corticogenesis (E8.5–E10.5), the specific role of Numb at later stages remains unknown. Methods and results: Here we used the mouse retina as a model system to study Numb function at different stages of neural development. We first used the Cre-loxP system to direct restricted in vivo inactivation of Numb in the retina from E10.5. Analysis of adult mutant retinas showed reduced neuronal differentiation, whereas analysis of embryonic mutant retinas showed reduced proliferation. It remained unclear, however, whether reduced neuronal differentiation was indirectly due to decreased proliferation at early stages or whether Numb directly controls neuronal differentiation at late stages. To test this model, we used retroviral vectors expressing Cre recombinase and GFP to infect NumbloxP/loxP mouse retinas at early and late stages of retinal development. Analysis of cell composition and size of each resulting knockout clone showed that early inactivation of Numb significantly reduces clone size, whereas late inactivation of Numb does not affect clone size but drastically decrease non-photoreceptor cell production. Conclusion: These results indicate that Numb promotes the progenitor fate at early stages of development, whereas it promotes the non-photoreceptor cell fate at later stages, suggesting a model in which Numb regulates different types of asymmetric cell divisions (Progenitor + Neuron or Neuron A + Neuron B) at distinct stages of development. doi: 10.1016/j.ijdevneu.2008.09.072 [P1.23] EphrinB3 and its receptor EphA4 control adult subventricular zone neurogenesis J. Ricard *, J. Salinas, D. Liebl University of Miami, USA *Corresponding author. Keywords: Ephrin; Subventricular zone; Neurogenesis
Ephrins and their Eph receptors regulate many developmental events in the central nervous system, and are down-regulated after birth. However, they are still expressed in discrete areas of the post-natal brain, in particular the subventricular zone (SVZ) where olfactory bulb (OB) neurons are continuously generated. Using gene-targeted knockout mice we studied the role of ephrinB3 and
849
its receptor EphA4 on adult neurogenesis. Mice lacking ephrinB3 exhibited increased proliferation in the SVZ and we located this protein just outside of the germinal zone. EphrinB3/ mice were also found to have a higher rate of cell death in the SVZ that may compensate for the increased proliferation. Moreover, ephrinB3 was found to be expressed around the rostral migratory stream and its absence hampered normal neuroblast migration to the OB. One of ephrinB3 receptors, EphA4, was also found to regulate neuroblast migration. These data provide evidence that ephrins and Eph receptors regulate several steps of the neurogenesis process in the subventricular zone of the adult brain. doi: 10.1016/j.ijdevneu.2008.09.073 [P1.24] Effects of inflammatory signaling on the outcome of allogeneic neural stem cell transplantation Z. Chen *, T. Palmer Stanford University, USA *Corresponding author. Keywords: Stem; Transplantation; Hippocampus; Inflammation
Transplantation of neural precursors or neural stem cells derived from ES cells or isolated from fetal and adult tissues is a promising strategy for treating neurological diseases. However, allogeneic and xenogeneic cellular grafts can elicit activation of both the innate and adaptive immune system. Despite the immunological privilege of the central nervous system, the effects of immune recognition on outcome are not fully understood. We have been evaluating immunologically matched and mismatched neural stem cells into different areas of adult mouse brain to determine the influence of immune signaling on the differentiation and survival of transplanted neural progenitors. Different brain areas represent unique niches that instruct the grafted cells towards different fates and we have found that mismatch-induced immune recognition most significantly effects the production of neurons when grafts are placed into neurogenic sites such as the hippocampus. Ongoing work examines interventions that may enhance neurogenesis and transplant efficacy. doi: 10.1016/j.ijdevneu.2008.09.074 [P1.25] Loss of the transcription factor TLX in dorsal progenitor cells leads to decreased cortical size and reduced anxiety E. Drill 1,*, E. Thiels 1, E.F. Greiner 2, G. Schutz 2, A.P. Monaghan 1 1
University of Pittsburgh, USA German Cancer Research Center, Germany *Corresponding author. 2
Keywords: Tailless; Cortex; Behavior; Conditional mutant
TLX (Nr2e1) is a transcription factor expressed in neural progenitor cells (PCs) throughout development and in regions of adult neurogenesis. TLX regulates proliferation in both embryonic and adult PCs. Loss of TLX leads to reductions in the adult in both the surface area and the thickness of the cerebral cortex, as well as reductions in other forebrain-derived structures including the dentate gyrus, the entorhinal cortex, the amygdala, and the striatum. These animals exhibit distinct behavioral abnormalities, including severe aggression, reduced anxiety, and late-onset epilepsy. These defects are associated with changes in both dorsal and ventral PCs. In