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Molecular mechanisms of synaptic differentiation and selective synapse assembly
Int. J. Devl Neuroscience 28 (2010) 639–641
Contents lists available at ScienceDirect
International Journal of Developmental Neuroscience journal homepage: www.elsevier.com/locate/ijdevneu
Plenary Speaker Abstracts
[PL1]
[PL2]
Epigenetic mechanisms in memory formation
Investigating the molecular basis of Rett syndrome
J.D. Sweatt
A. Bird
UAB School of Medicine, USA
University of Edinburgh, UK
This presentation will address the idea that conservation of epigenetic mechanisms for information storage represents a unifying model in biology, with epigenetic mechanisms being utilized for cellular memory at levels from behavioral memory to development to cellular differentiation. The area of epigenetics is unfamiliar to many neurobiologists: epigenetic mechanisms typically involve alterations in chromatin structure, which in turn regulate gene expression. “Epigenetics” is functionally equivalent to the mechanisms allowing stable maintenance of gene expression that involve physically “marking” DNA or its associated proteins through post-translational modification. Thus, regulation of chromatin structure and regulation of direct methylation of DNA are the principal mechanisms of epigenetic regulation. Do epigenetic mechanisms operate in behavioral memory formation? We have generated several lines of evidence that support this idea. (1) Contextual fear conditioning triggers alterations in hippocampal histone acetylation, and contextual latent inhibition training triggers similar but distinct changes in histone acetylation. (2) The methyl-DNA binding protein MeCP2 (the Rett mental retardation syndrome gene product) alters chromatin structure and regulates hippocampal LTP and memory formation. (3) Inhibitors of DNA methylation block both hippocampal LTP and associative learning in vivo. An emerging idea is that the regulation of chromatin structure, mechanistically via histone modification and DNA methylation, may mediate long-lasting behavioral change and learning and memory. We find this idea fascinating because similar mechanisms are used for triggering and storing long-term “memory” at the cellular level, for example when cells differentiate.
MeCP2 was initially identified as an abundant protein in the brain, with an affinity for methylated DNA in vitro. Subsequent transfection experiments showed that it can recruit corepressor complexes and inhibit gene expression in vivo. MeCP2 was therefore thought to repress specific gene targets and the aetiology of Rett syndrome was proposed to result from aberrant gene expression in the MeCP2-deficient brain. Although gene expression is perturbed in the Mecp2-null mouse brain, few specific targets have been verified and alternative hypotheses for MeCP2 function have been put forward. In an attempt to distinguish these hypotheses, we purified neuronal and glial nuclei and established that the amount of MeCP2 is unexpectedly high in neurons. Chromatin immunoprecipitation experiments showed widespread binding of MeCP2, consistent with its high abundance. The pattern of binding tracks the distribution of 5-methylcytosine. Further work analysed the effects of MeCP2 deficiency in neurons on chromatin structure/modification and on expression of repetitive elements. Our data suggest that a major role of MeCP2 is to create a repressive chromatin environment by associating with chromosomes in a DNA methylation-dependent manner. These findings will be discussed in the light of the reversibility of Rett syndrome-like symptoms in the mouse model.
doi:10.1016/j.ijdevneu.2010.07.003
doi:10.1016/j.ijdevneu.2010.07.004 [PL3] Molecular mechanisms of synaptic differentiation and selective synapse assembly P. Scheiffele 1,2,∗ , T. Iijima 1 , H. Witte 1 , K. Wu 2 , F. Boukhtouche 1 , A. Kalinovsky 2 1 2
University of Basel, Switzerland Columbia University, USA
The assembly of functional neuronal circuits during development relies on an intricate interplay of cellular interactions, molecular recognition signals, and neuronal activity-dependent processes. The goal of our work is to understand the molecular
0736-5748/$36.00
640
Plenary Speaker Abstracts / Int. J. Devl Neuroscience 28 (2010) 639–641
mechanisms underlying the differentiation of synaptic junctions and the signaling systems that restrict synapse formation and/or stability to the appropriate target cells in vivo. We screened for cell adhesion and signaling molecules that can either stabilize or destabilize synaptic junctions. In this effort, we identified Bone Morphogentic Proteins as novel inhibitory regulators of synapse formation in the mouse cerebellum. A second focus of our studies has been on the neuroligin–neurexin protein complex, a heterophilic adhesion system at central synapses with “synaptogenic” activities. Neuroligins and neurexins are encoded by multiple genes and substantial molecular diversity is generated at the level of alternative splicing. We have characterized isoform-specific functions of individual neuroligin and neurexin isoforms. Moreover, we have uncovered a signal transduction pathway which dynamically regulates alternative splicing of the neurexin mRNAs in response to neuronal activity. Copy number variations and mutations in the human neuroligin and neurexin genes have been identified in patients with autism-spectrum disorders. Therefore, our insights into the basic molecular mechanisms of neuroligin and neurexin functional regulation may be helpful with respect to understanding the neuronal abnormalities underlying these disorders. doi:10.1016/j.ijdevneu.2010.07.005 [PL4] FoxP2 in songbirds C. Scharff Freie Universität Berlin and Max Planck Institute for Molecular Genetics, Germany The FOXP2 gene is essential for developing the full articulatory power of human language and was apparently the target of positive selection during recent human evolution. Mutations of FOXP2 cause a speech and language disorder that compromises the fluent production of words and the correct use and comprehension of grammar. FOXP2 patients have structural and functional abnormalities in the striatum of the basal ganglia, where high levels of FOXP2 expression occur. Since human speech and learned vocalizations in songbirds bear behavioral and neural parallels, songbirds provide a genuine model for investigating the basic principles of speech and its pathologies. We therefore compared FoxP2 sequences of three orders of birds capable of vocal imitations with birds lacking song learning ability but found no correlation between a particular version of the FoxP2 coding region and a species’ capacity for vocal imitation. However, we did find correlations between FoxP2 expression levels in Area X, a basal ganglia structure necessary for song acquisition, and times of vocal plasticity, both in young zebra finches and adult canaries. We therefore downregulated FoxP2 in Area X of juvenile finches, using lentivirus-mediated RNAi to determine effects on song development. We found that FoxP2 knockdown in Area X resulted in incomplete and inaccurate tutor imitation. Inaccurate and incomplete imitation of sounds are also core deficits of orofacial dyspraxia. Together, our findings suggest that normal auditory-guided vocal motor learning in the basal ganglia of songbirds requires FoxP2. These findings provide the first example of a functional gene analysis in songbirds, a widely studied neuroethological model system. They also highlight the fact that FoxP2 is playing a role in differentiated, post-natal neural circuits. The fact that FoxP2 is involved in both birdsong and speech implies that some of the molecular substrates for the uniquely human capacity of language are not exclusive to the hominid lineage.
Ongoing studies examine the molecular targets of FoxP2 in vitro and in vivo, the interaction of FoxP2 with its dimerization partners FoxP1 and FoxP2, and the neurophysiological function of FoxP2 in striatal spiny neurons in a brain region critical for song learning.
Acknowledgement Funding provided by DFG SFB 665. doi:10.1016/j.ijdevneu.2010.07.006 [PL5] Epilepsy as a prototype neurodevelopmental disorder J.L. Noebels Baylor College of Medicine, USA Molecular genetic strategies have taken precise aim at the enigma of epilepsy, the most common severe neurological disorder, and a frequent comorbid phenotype of a diverse spectrum of disorders affecting the intellect in developing brain. Epilepsy can result in abnormal brain development, and abnormal brain development can result in epilepsy. Critical progress in the discovery of genes linked with human epilepsies has been made in the last decade. While the defined monogenic syndromes recognized to date account for only a minority of the large clinical population with idiopathic seizure disorders, the functional diversity of these genes provide extraordinary insight into the biological control pathways of synchronous neuronal activity in the brain. Genes for epileptogenesis include a broad range of molecules regulating brain assembly, activity, and cell death. The underlying human epilepsy syndromes discovered to date can be provisionally divided into three broad categories. The first consists of dynamic excitability defects in neuronal ion channels, receptors, and the regulation of synaptic transmission. The second includes developmental cortical malformations and cellular migration disturbances leading to early structural changes in neural connectivity. The third comprises errors of cellular homeostasis and intermediary metabolism leading to oxidative deficiency, aberrant proteolysis, and neurodegeneration. Spontaneous mutations and targeted mutagenesis in experimental models reveal an even more extensive array of genes associated with epilepsy that affect synaptogenesis, vesicle release, and neuroplasticity. For each molecule pinpointed by the single gene disorders, neurobiological analysis in orthologous mouse models of the human disease can determine its effects on developing neurons, and the developmental stage when it interferes with the excitability of neural networks. Distinct, gene specific patterns of molecular neuroplasticity and synaptic reorganization triggered by the seizures themselves contribute to the intervening neural mechanisms, and the appearance or disappearance of seizures at later stages of a developmental disorder. doi:10.1016/j.ijdevneu.2010.07.007 [PL6] Neuroimaging of human development and neurodevelopmental disorders J. Giedd National Institute of Mental Health, USA Magnetic resonance imaging (MRI), which combines a powerful magnet, radio waves, and sophisticated computer technology to provide exquisitely accurate pictures of brain anatomy and physiology, has opened an unprecedented window into the biology of
Contents lists available at ScienceDirect
International Journal of Developmental Neuroscience journal homepage: www.elsevier.com/locate/ijdevneu
Plenary Speaker Abstracts
[PL1]
[PL2]
Epigenetic mechanisms in memory formation
Investigating the molecular basis of Rett syndrome
J.D. Sweatt
A. Bird
UAB School of Medicine, USA
University of Edinburgh, UK
This presentation will address the idea that conservation of epigenetic mechanisms for information storage represents a unifying model in biology, with epigenetic mechanisms being utilized for cellular memory at levels from behavioral memory to development to cellular differentiation. The area of epigenetics is unfamiliar to many neurobiologists: epigenetic mechanisms typically involve alterations in chromatin structure, which in turn regulate gene expression. “Epigenetics” is functionally equivalent to the mechanisms allowing stable maintenance of gene expression that involve physically “marking” DNA or its associated proteins through post-translational modification. Thus, regulation of chromatin structure and regulation of direct methylation of DNA are the principal mechanisms of epigenetic regulation. Do epigenetic mechanisms operate in behavioral memory formation? We have generated several lines of evidence that support this idea. (1) Contextual fear conditioning triggers alterations in hippocampal histone acetylation, and contextual latent inhibition training triggers similar but distinct changes in histone acetylation. (2) The methyl-DNA binding protein MeCP2 (the Rett mental retardation syndrome gene product) alters chromatin structure and regulates hippocampal LTP and memory formation. (3) Inhibitors of DNA methylation block both hippocampal LTP and associative learning in vivo. An emerging idea is that the regulation of chromatin structure, mechanistically via histone modification and DNA methylation, may mediate long-lasting behavioral change and learning and memory. We find this idea fascinating because similar mechanisms are used for triggering and storing long-term “memory” at the cellular level, for example when cells differentiate.
MeCP2 was initially identified as an abundant protein in the brain, with an affinity for methylated DNA in vitro. Subsequent transfection experiments showed that it can recruit corepressor complexes and inhibit gene expression in vivo. MeCP2 was therefore thought to repress specific gene targets and the aetiology of Rett syndrome was proposed to result from aberrant gene expression in the MeCP2-deficient brain. Although gene expression is perturbed in the Mecp2-null mouse brain, few specific targets have been verified and alternative hypotheses for MeCP2 function have been put forward. In an attempt to distinguish these hypotheses, we purified neuronal and glial nuclei and established that the amount of MeCP2 is unexpectedly high in neurons. Chromatin immunoprecipitation experiments showed widespread binding of MeCP2, consistent with its high abundance. The pattern of binding tracks the distribution of 5-methylcytosine. Further work analysed the effects of MeCP2 deficiency in neurons on chromatin structure/modification and on expression of repetitive elements. Our data suggest that a major role of MeCP2 is to create a repressive chromatin environment by associating with chromosomes in a DNA methylation-dependent manner. These findings will be discussed in the light of the reversibility of Rett syndrome-like symptoms in the mouse model.
doi:10.1016/j.ijdevneu.2010.07.003
doi:10.1016/j.ijdevneu.2010.07.004 [PL3] Molecular mechanisms of synaptic differentiation and selective synapse assembly P. Scheiffele 1,2,∗ , T. Iijima 1 , H. Witte 1 , K. Wu 2 , F. Boukhtouche 1 , A. Kalinovsky 2 1 2
University of Basel, Switzerland Columbia University, USA
The assembly of functional neuronal circuits during development relies on an intricate interplay of cellular interactions, molecular recognition signals, and neuronal activity-dependent processes. The goal of our work is to understand the molecular
0736-5748/$36.00
640
Plenary Speaker Abstracts / Int. J. Devl Neuroscience 28 (2010) 639–641
mechanisms underlying the differentiation of synaptic junctions and the signaling systems that restrict synapse formation and/or stability to the appropriate target cells in vivo. We screened for cell adhesion and signaling molecules that can either stabilize or destabilize synaptic junctions. In this effort, we identified Bone Morphogentic Proteins as novel inhibitory regulators of synapse formation in the mouse cerebellum. A second focus of our studies has been on the neuroligin–neurexin protein complex, a heterophilic adhesion system at central synapses with “synaptogenic” activities. Neuroligins and neurexins are encoded by multiple genes and substantial molecular diversity is generated at the level of alternative splicing. We have characterized isoform-specific functions of individual neuroligin and neurexin isoforms. Moreover, we have uncovered a signal transduction pathway which dynamically regulates alternative splicing of the neurexin mRNAs in response to neuronal activity. Copy number variations and mutations in the human neuroligin and neurexin genes have been identified in patients with autism-spectrum disorders. Therefore, our insights into the basic molecular mechanisms of neuroligin and neurexin functional regulation may be helpful with respect to understanding the neuronal abnormalities underlying these disorders. doi:10.1016/j.ijdevneu.2010.07.005 [PL4] FoxP2 in songbirds C. Scharff Freie Universität Berlin and Max Planck Institute for Molecular Genetics, Germany The FOXP2 gene is essential for developing the full articulatory power of human language and was apparently the target of positive selection during recent human evolution. Mutations of FOXP2 cause a speech and language disorder that compromises the fluent production of words and the correct use and comprehension of grammar. FOXP2 patients have structural and functional abnormalities in the striatum of the basal ganglia, where high levels of FOXP2 expression occur. Since human speech and learned vocalizations in songbirds bear behavioral and neural parallels, songbirds provide a genuine model for investigating the basic principles of speech and its pathologies. We therefore compared FoxP2 sequences of three orders of birds capable of vocal imitations with birds lacking song learning ability but found no correlation between a particular version of the FoxP2 coding region and a species’ capacity for vocal imitation. However, we did find correlations between FoxP2 expression levels in Area X, a basal ganglia structure necessary for song acquisition, and times of vocal plasticity, both in young zebra finches and adult canaries. We therefore downregulated FoxP2 in Area X of juvenile finches, using lentivirus-mediated RNAi to determine effects on song development. We found that FoxP2 knockdown in Area X resulted in incomplete and inaccurate tutor imitation. Inaccurate and incomplete imitation of sounds are also core deficits of orofacial dyspraxia. Together, our findings suggest that normal auditory-guided vocal motor learning in the basal ganglia of songbirds requires FoxP2. These findings provide the first example of a functional gene analysis in songbirds, a widely studied neuroethological model system. They also highlight the fact that FoxP2 is playing a role in differentiated, post-natal neural circuits. The fact that FoxP2 is involved in both birdsong and speech implies that some of the molecular substrates for the uniquely human capacity of language are not exclusive to the hominid lineage.
Ongoing studies examine the molecular targets of FoxP2 in vitro and in vivo, the interaction of FoxP2 with its dimerization partners FoxP1 and FoxP2, and the neurophysiological function of FoxP2 in striatal spiny neurons in a brain region critical for song learning.
Acknowledgement Funding provided by DFG SFB 665. doi:10.1016/j.ijdevneu.2010.07.006 [PL5] Epilepsy as a prototype neurodevelopmental disorder J.L. Noebels Baylor College of Medicine, USA Molecular genetic strategies have taken precise aim at the enigma of epilepsy, the most common severe neurological disorder, and a frequent comorbid phenotype of a diverse spectrum of disorders affecting the intellect in developing brain. Epilepsy can result in abnormal brain development, and abnormal brain development can result in epilepsy. Critical progress in the discovery of genes linked with human epilepsies has been made in the last decade. While the defined monogenic syndromes recognized to date account for only a minority of the large clinical population with idiopathic seizure disorders, the functional diversity of these genes provide extraordinary insight into the biological control pathways of synchronous neuronal activity in the brain. Genes for epileptogenesis include a broad range of molecules regulating brain assembly, activity, and cell death. The underlying human epilepsy syndromes discovered to date can be provisionally divided into three broad categories. The first consists of dynamic excitability defects in neuronal ion channels, receptors, and the regulation of synaptic transmission. The second includes developmental cortical malformations and cellular migration disturbances leading to early structural changes in neural connectivity. The third comprises errors of cellular homeostasis and intermediary metabolism leading to oxidative deficiency, aberrant proteolysis, and neurodegeneration. Spontaneous mutations and targeted mutagenesis in experimental models reveal an even more extensive array of genes associated with epilepsy that affect synaptogenesis, vesicle release, and neuroplasticity. For each molecule pinpointed by the single gene disorders, neurobiological analysis in orthologous mouse models of the human disease can determine its effects on developing neurons, and the developmental stage when it interferes with the excitability of neural networks. Distinct, gene specific patterns of molecular neuroplasticity and synaptic reorganization triggered by the seizures themselves contribute to the intervening neural mechanisms, and the appearance or disappearance of seizures at later stages of a developmental disorder. doi:10.1016/j.ijdevneu.2010.07.007 [PL6] Neuroimaging of human development and neurodevelopmental disorders J. Giedd National Institute of Mental Health, USA Magnetic resonance imaging (MRI), which combines a powerful magnet, radio waves, and sophisticated computer technology to provide exquisitely accurate pictures of brain anatomy and physiology, has opened an unprecedented window into the biology of