Brain development phenotyping of IMPC lethal mutant mice

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Abstract: The mechanisms by which neural stem cells build the brain from a simple epithelial tube is a compelling mystery of biology. Mouse genetics has been one of the most powerful tools to discover the genes and processes involved in building a healthy brain, or in neurodevelopmental disorders that affect brain structure or function. The library of targeted mutations created by the International Mouse Phenotyping Consortium (IMPC) provides a highly valuable resource for understanding those genes and processes. Many mutations that cause neurodevelopmental phenotypes are lethal, either due to the brain defect or to pleiotropic functions of the gene in other organs essential for viability. Thus, the bank of lethal mutants at IMPC provides an enriched set of candidate genes required for brain development. However, changes in brain structure or wiring are difficult to detect without the right tools and expertise. We propose to apply our expertise to phenotype selected knockout lines that are likely to have neurodevelopment defects, based on gene expression, function, and/or known mutation in a human developmental disorder. This is in response to an FOA to characterize developmental defects in lethal IMPC mutants. We will combine non-hypothesis driven gross phenotyping with hypothesis-driven analysis of a few selected brain development mutants. To add value and efficiency to this screen, subsets of mutants will also be tested by co-investigators for inner ear development phenotypes, and placenta, gastrulation, or neural tube defects. For the first tier of phenotyping, lines will be tested for age of lethality and phenotyped for gross abnormalities of brain, inner ear, spinal cord, and body development. Tier 2 phenotyping will incorporate histopathology of brain, inner ear, and placenta, since many structural defects in these organs cannot be ascertained without sectioning and staining. We will test for proliferation, layering, and axon tract defects. Tier 3 phenotyping will focus on a small number of mutants with both abnormal brain phenotypes and gene functions in cytokinesis, to address our hypothesis: that different defects in cytokinesis of cortical neural stem cells underlie a variety of brain malformations. We will make use of methods we have established for quantitative analysis of cytokinetic furrowing and abscission defects in developing mouse cortex. In all stages of phenotyping, heterozygotes and homozygotes will be compared to controls quantitatively and with statistical rigor. Data will be shared with IMPC for the benefit of the community. Our team of three investigators has a combined >50 years of expertise working on cellular bases of organ development in the mouse model, and forward and reverse genetics. Through this project , we will discover new mouse models for developmental disorders of the brain, inner ear, and placenta, and will provide important new insights into the mechanisms of neural stem cell divisions and cellular defects underlying brain malformations.