The research we propose will use mouse models to identify the molecular mechanisms underpinning development of the retina. The mouse models, all developed by the applicant, include a conditional allele of the Down syndrome cell adhesion molecule, Dscam, as well as an allelic series of mouse mutant Dscam strains and a null allele of the Dscam homologue Dscam-like1 (Dscaml1). Dscam and Dscam- Like1 are essential for normal development of the nervous system and Dscam is proposed to contribute to the pathology of Down syndrome. In the retina, Dscam is required for soma mosaic spacing, regulation of cell number and neurite arborization and lamination. Our published results concerning Dscam and Dscaml1 are the first demonstrations of mutations found to ablate mosaic patterning and the first genes shown to mediate isoneuronal and heteroneuronal repulsion in vertebrates. Specific Aims: We propose to use the Dscam and Dscaml1 mutant mouse models to discover mechanisms underpinning development of the retina and to probe the function of Dscam in the mammalian nervous system. This will be accomplished by testing the following hypotheses detailed in this research proposal. Hypotheses: 1) We will test the hypothesis that DSCAM mediates multiple distinct functions using an allelic series and conditional allele of Dscam mouse mutant lines to genetically and temporally isolate Dscam-dependent developmental processes. 2) We will test the hypothesis that DSCAM mediates adhesion between cell types and repulsion within cell types and that DSCAM activity in the retina is mediated by homophillic interactions and not by a ligand-receptor mechanism by using a conditional allele coupled to cell type specific deletion. 3) We will test the hypothesis that Dscam and Dscaml1 regulate normal developmental cell death. Long-term goals: This research will uncover fundamental aspects of neural organization and provide the funding necessary for Dr. Fuerst to establish a successful academic career focused on hypothesis driven biomedical research. Significance: Neurite arborization, regulation of cell number and soma mosaic spacing are fundamental aspects of neurodevelopment that are not currently well understood at the molecular level in vertebrates. Our preliminary research indicates that DSCAM plays a vital role in mediating these processes in the mammalian nervous system. Identifying mechanisms by which DSCAM functions using a series of mouse mutant alleles and a conditional allele will contribute to our understanding of nervous system development and the causation of disorders associated with neural dysgenesis and also contribute valuable research models to the neuroscience community.
PUBLIC HEALTH RELEVANCE: The primary goal of the proposed work is to understand how molecular recognition cues facilitate neural patterning. Research will focus on discovering the mechanisms by which two recognition cues; the Down Syndrome Cell Adhesion Molecule (Dscam) and its homologue Dscam-like1 (Dscaml1), mediate circuit formation within the retina. Both Dscam and Dscaml1 are required for neurite lamination, neurite arborization and regulation of cell number. Therefore, understanding the mechanism by which these molecules function will advance scientific understanding of neural development on multiple fronts. Furthermore, decreasing Dscam dosage decreases the incidence of retinal developmental cell death suggesting that the retina may provide an excellent system in which to model enhanced developmental cell death of neurons that occurs in Down syndrome patients, who overexpress Dscam as a result of Chromosome 21 trisomy.