Molecular Studies of Neural Tube Defect Development in the Mouse Embryo

The thesis describes studies of the development of neural tube defects (NTD) in genetically predisposed mice, specifically the curly tail and loop-tail mutants. The curly tail mouse exhibits delay or failure of closure of the neural tube at the posterior neuropore and is a model for low spinal NTD in humans. In vivo supplementation of embryos with the vitamin, inositol, significantly reduces the incidence of spinal defects raising the possibility of using inositol to prevent a proportion of NTD in humans. Moreover, inositol treatment of embryos in culture minimises the delay in posterior neuropore closure that is known, from previous studies, to lead directly to development of NTD. The mechanism of action of inositol has been examined using in vitro inhibitors and activators, measurements of inositol incorporation and analysis of gene expression in cultured embryos. The findings suggest a model that involves an increased flux through the inositol/lipid cycle which leads to activation of protein kinase C and upregulation of expression of retinoic acid receptor-β in the hindgut, the affected tissue in the curly tail mutant. The loop-tail mutant mouse is a model for craniorachischisis in humans; homozygous embryos exhibit failure of initial closure of the neural folds resulting in an open neural tube from the midbrain/hindbrain boundary along the entire body axis. Loop-tail embryos are identified by PCR analysis prior to the failure of neural tube closure. Analysis of gene expression by whole mount in situ hybridisation reveals abnormal expression of sonic hedgehog and netrin-1 in the notochord and floor plate of homozygous mutant embryos suggesting that defects in the development of these tissues may contribute to the development of NTD.