Mouse mutants that perturb cortical patterning have provided considerable insight into the development of the mammalian brain. We have previously undertaken a project to generate models of human congenital defects by screening ENU-mutagenized mice for recessive mutations affecting late embryonic development. The screen incorporated a genetic mapping component, with the intent to facilitate the positional cloning and functional characterization of the mutant genes. The strategy has worked well, and we have generated many mice with phenotypes similar to human malformation syndromes and birth defects. In this proposal we aim to target cortical development, with the goal of identifying and cloning additional mutants that will be useful for understanding how the mammalian brain is patterned. Specifically, we plan to screen for mice that have abnormalities of brain morpholology and histology. We will also screen for mutations that perturb patterning of reporter genes that mark specific anatomical structures, A third strategy is to screen for mutations that have a genetic interaction with known cortical patterning genes such as Lis1. We have developed efficient strategies for genetic mapping and positional cloning, and we are currently working on rapid methods of mutation validation using RNAi. Finally, for a subset of mutations that have relatively specific effects on cortical development, we plan to pursue in-depth analysis, including a collaborative effort with investigators at the Allen Institute for Brain Science utilizing high-throughput technologies for in situ expression analysis. Depending upon the nature of the mutated gene, we will pursue functional studies as appropriate.
. We propose to treat mice with the chemical ethyl-nitrosourea (ENU), which causes mutations in DNA. We will examine the progeny of treated mice to assess whether they have disorders of brain development. We are particularly interested in those that have relatively subtle effects;that is, which appear to specifically affect the formation of the brain, but not other organs. Once we have generated these mutants, we will use state-of-the-art methods of genome analysis to identify the mutated gene. With these in hand, we can begin to evaluate what developmental pathways are affected in these abnormal mice. Understanding the formation of the brain will likely help us to understand the roots of the many brain diseases affecting one in five Americans today (www.ninds.nih.gov). These diseases include developmental disorders (including autism), degenerative diseases of adult life, metabolic diseases, and brain tumors. Defects in neuronal migration within the forebrain lead to mental retardation, epilepsy and severe learning disabilities. The forebrain is also primarily affected in many other diseases such as Parkinson's and Huntington's diseases and schizophrenia. Significant efforts, both public and private, are currently underway to begin to identify more of the genes expressed in the brain at various stages as well as their expression patterns. This information, combined with the mutational analysis we plan, will help uncover the basic steps required for normal brain development.
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