There are two related long-term goals of the proposed research. First, to determine the mechanisms through which the receptor tyrosine kinase Met signaling system influences forebrain development. Second, to define the relationship between MET gene regulation and altered forebrain development that may lead to functional impairments characteristic of autism spectrum disorder (ASD). MET and its ligand, hepatocyte growth factor (HGF), have been implicated in the development and maturation of neuronal circuits in vitro. In vivo, indirect genetic manipulation of HGF-Met signaling results in alterations in cortical interneuron development, intermittent seizures, increased anxiety and reduced social behavior in mice. Our preliminary data from the conditional deletion of Met in the neocortex provides direct evidence that Met signaling is involved in the structural and biochemical maturation of synapses. Moreover, we discovered that a single nucleotide polymorphism (SNP rs1858830) in the 52 transcriptional regulatory region of the human MET gene is strongly associated with ASD (P=5X10-6). This variant is functional, as it reduces gene transcription by interfering with transcription factor binding. This has clinical validity, as we have shown recently that MET protein expression is reduced to 50% of control levels in the temporal cortex of subjects with ASD compared to controls. The convergence of the human genetic and biochemical studies in ASD and basic developmental neurobiology suggests that MET signaling is important for the proper assembly of forebrain circuits, with dysregulation leading to functional disruptions in both model systems and in humans. In this renewal application, we propose to take advantage of the convergence of basic and clinical research data, organized around three specific aims to address the role of MET in neocortical development, the factors that contribute to MET gene regulation, and the influence of the ASD-associated human genetic regulatory variant on MET-related forebrain ontogeny.
Aim 1 will determine the impact of direct elimination of Met signaling in the cerebral cortex using mice in which Emx1Cre conditionally deletes Met from the dorsal pallium. The goal of these studies is to define changes in dendritic and synaptic architecture, and in synaptic signaling systems.
Aim 2 will define and experimentally manipulate, in cell lines, the transcription factors and assembled complex that regulate human MET gene transcription. The regulation of MET by epigenetic mechanisms in ASD cases of postmortem brains and peripheral cells from patients will be examined in methylation studies of the extensive CpG island in the 52 regulatory region of the gene.
In Aim 3, new `humanized'mouse lines will be engineered that contain the human 52 regulatory sequence that has either the `G'or `C'rs1858830 allele and the CpG island. The goals of this aim are to determine how the ASD-associated `C'allele influences MET gene transcription and brain development in an in vivo model system, and to define the influence of epigenetic regulation of gene expression over time.
The CDC notes that ASD affects 1 in every 150 children in the United States. The research proposal will directly investigate directly a risk gene for ASD by determining how alterations in gene expression impact brain development. This project includes basic and clinical translational studies that will provide insight into gene- gene and gene-environment interactions that may underlie atypical brain functions in ASD.
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