Genetic, Cellular and Molecular Defects in Mouse Mutants with Severe Neural Tube Defects

Neural tube defects are one of the most common birth defects. This thesis includes genetic, molecular and cellular analysis of three mouse mutants with neural tube defects. chuzhoi was identified from an ENU G3 screen and exhibits craniorachischisis through failure to initiate neural tube closure. In this thesis, I show that chuzhoi carries a point mutation affecting a splice-site in the Ptk7 gene, leading to addition of three extra amino acids in the protein. Through phenotypic analysis I show that chuzhoi has a wider midline and a smaller length to width ratio, suggesting a defect in convergent extension. Previous work has shown that the Planar Cell Polarity (PCP) signalling pathway is required for the initiation of neural tube closure. Through genetic crosses between chuzhoi and mutants of PCP signalling, I show that Ptk7 can influence the PCP pathway without being a direct component of the pathway. Carrying a mutation in Scribble, Circletail is another mutant displaying craniorachischisis. Scribble in Drosophila is required for the establishment of apical-basal polarity and to control the rate of cell proliferation. I show that mouse Scribble is not required for the establishment of apical-basal polarity nor to control proliferation, during neural tube closure. Previous work in zebrafish has shown that the axis elongation of an embryo requires PCP-dependent orientation of cell division. Here, I show that the orientation of cell division is random in mice during the shaping of the neural plate prior to the initiation of the neural tube closure. Mouse mutants of Tulp3 exhibit spina bifida and exencephaly. The molecular role of Tulp3 is largely unknown; however, domains present in the Tulp3 protein suggest that it may act as a transcription factor and/or be involved in protein-protein interactions. I provide evidence to suggest that Tulp3 is not likely to function as a transcription factor but may participate in many protein-protein interactions to deliver its role during mouse embryogenesis