Abstracts

Rationale: A number of molecular and genetic reports provide evidence that GABAergic deficiency contributes substantially to the etiology of autism. Many of the disrupted genes associated with autism contribute to the differentiation and migration of GABAergic neurons. One of these genes, human neuropilin 2 (NPN2), is a receptor for class III semaphorins, a group of axonal guidance genes that may regulate migration, and differentiation of hippocampal interneurons. The gene encoding NPN2 is located in the putative autism susceptibility loci (chromosome 2q34), and single nucleotide polymorphisms (SNPs) found at this loci are associated with the development of autism in Chinese populations. Mice that are homozygous null for the NPN2 gene experience seizures and present an abnormal hippocampal interneuron phenotype including deficient numbers of GABA+, Neuropeptide Y+ (NPY), and Parvalbumin+ (Parv) neurons in the hippocampus. Methods: We have investigated the genetic regulation of Semaphorin 3F signaling in cell specific ablation experiments.Results: Deletion of Sema 3F gene (a gene encoding one of the class III semaphorins that act at the NPN2 receptor) in migrating postmitotic GABAergic neurons but not postnatal neurons leads to deficient cell numbers of GABA+ and Parv+ neurons in adult murine hippocampus. While these SNPs are associated with the NPN2 gene loci, the transcriptional regulators of axon guidance genes associated with hippocampal interneuron development are largely unknown. However data suggests that cyclic AMP linked transcription factors, such as p300 and CBP, may play an important role in hippcampal interneuron development, and deletion of the p300 DNA binding element in the human or mouse NPN2 promoter increases promoter activation. We hypothesize that concerted regulation of transcription factors such as p300 and DLX1/2 is necessary for proper gene expression of NPN2. Appropriate expression of this receptor is necessary for proper signaling by Sema 3F, thereby directing the migration and differentiation of hippocampal interneurons.Using EMSA assays, we show that the NPN2 promoter is a specific target of p300 in neuroblastoma cells. siRNA experiments confirm loss of p300 expression in neuroblastoma cells increases endogenous NPN2 transcripts.Conclusions: These studies support our hypothesis that regulation by p300 is necessary for proper expression of NPN2 and suggests that Sema3F signaling through the NPN2 receptor is essential to proper placement of hippocampal interneurons during development. Supported by the American Epilepsy Society/Epilepsy Foundation.