The goal of this ongoing project is to characterize the gene mutated in the Crooked tail (Cd) mouse as a new locus associated with folic acid (FA) sensitive neural tube defects (NTD). Homozygous Cd are prone to rostral NTD and those completing neurulation display a subtle cortical dysplasia. In the first 3 years of funding, we have shown that the incidence of NTD is reduced in Cd by dietary folate in a manner closely resembling clinical observation, making it an important model for human NTD. Linkage analysis has fine-mapped the Cd locus to a 0.2 cM region of chromosome 6. Physical mapping and sequencing of the Cd critical region has identified 3 candidate genes. The project will identify the Cd gene, investigate the pathogenesis of its CNS malformations at the cellular and molecular levels and examine the relation between folate metabolism and these defects. First, the Cd gene will be sought through positional cloning and testing of identified candidates. Linkage analysis has beer completed and a genomic DNA contig covering the critical region has been established. In the renewal period we will identify Cd by: (a) cloning cDNAs corresponding to the genomic contig; (b) analysis of candidate genes from the region for large and small mutations in Cd mice. The identity of the gene producing Cd will be confirmed through demonstration that the phenotype can be rescued by introduction of BACs encompassing at entire candidate gene. Alternatively, the putative Cd mutation will be "knocked-in" to recapitulate the Cd phenotype. Second, The mechanisms leading to the Cd phenotype will be determined, whether due to altered cell proliferation, neuronal migration or programmed cell death. Morphogenesis of individual Cd embryos in culture will be examined by time-lapse confocal microscopy. In addition Cd brain histogenesis will be defined using markers of neural fate determination and CNS pattern formation. Third, Investigation of dietary folate will continue, to determine whether FA alters the proliferation of cells during neurulation, and whether FA can also ameliorate Cd cerebral cortical maldevelopment. Fourth, Functional studies of Cd will begin with structural analysis of the gene product. The status of FA-related metabolic pathways in Cd animals will be investigated for clues to potential mechanisms leading to FA-sensitive NTD. Function will be investigated by over-expression of Cd in mice, introduced by BAC vectors to permit transgene expression in appropriate temporal and anatomic sequence. Further functional studies will inactivate Cd in normal mice by a conditional homologous recombinant knockout. Study of the genetic, molecular and cellular events leading to abnormalities in Cd will contribute to mechanistic understanding of NTD and may lead to strategies for prenatal assessment of an individual family?s risk and tailored prevention of human brain maldevelopment.