Genetic analysis of neural tube defects in the mouse

Loop-tail is a mouse model for the human condition of craniorachischisis, the most severe form of neural tube defect. In homozygous mutants the initation of neural tube closure in the future cervical region (Closure 1) fails to occur, such that the neural folds remain open from the midbrain throughout the spine. Previous studies indicate that loop-tail (Lp) is linked to markers on distal Chromosome 1, and this thesis reports the generation of an accurate genetic map around Lp. An intraspecific backcross was generated between CBA/Ca (a normal inbred strain) and LPT/Le (the inbred strain carrying the Lp mutation) and the loop-tailed offspring were genotyped for a number of DNA markers on distal Chromosome 1. The analysis of the recombination frequencies between Lp and these markers localised Lp to a 1.19 cM interval between DlMitl 13 and Crp/Fcerla. This is within a region of mouse Chromosome 1 that is syntenic with human Chromosome Iq21-q23, suggesting that a human homologue of loop-tail is likely to reside in this region. A number of genes are known to map in this region, in either mouse or human, and this thesis reports the assessment of these genes as candidates for Lp using a combination of genetic mapping and expression analysis. Tyro10, Tagln2 and Mor23 are shown to recombine with Lp, and are therefore excluded as candidates, and wholemount in situ hybridisation with Girk3 and DlUcla4 reveals that these genes are not expressed at this stage of embryogenesis. Other candidate genes considered in this study include Nhlhl, Peal5, Copa and AA033172, and this thesis reveals the embryonic expression of these candidates and reports the search for coding region mutations by dideoxy sequencing