International Mammalian Genome Society

G13 Transcript Mapping in the Lp Critical Region on Mouse Chromosome 1

Kit Doudney, Jane Eddleston, Claire Braybrook, Aysha Itani, Muly Tham, Jennifer Murdoch^a, Andrew Copp^a and Philip Stanier. Department of Fetal and Maternal Medicine, Division of Paediatrics, Obstetrics and Gynaecology, Imperial College School of Medicine, Queen Charlotte's and Chelsea Hospital, Goldhawk Road, London W6 0XG; ^aNeural Development Unit, Institute of Child Health, University College London, WC1N 1EH

Neural tube defects (NTD) are among the most common congenital defects in the human. The underlying defects are difficult to elucidate because of a complex, multifactorial mode of inheritance. The Loop-tail mouse-mutant (Lp), however, is highly penetrant and provides a useful model for the most severe human NTD, cranio-rachischisis. The most characteristic feature is a failure to achieve the first closure event of neurulation (closure 1) resulting in an open neural tube from mid brain to base of the spine. Positional cloning was initiated with a linkage analysis in a large intraspecific backcross, which localised Lp to a 1.2 cM region of mouse chromosome 1. A 3.2 Mb YAC contig was constructed with the aid of novel STSs identified by cross screening human and mouse EST databases. This method simultaneously identified candidate transcripts from the region. Refined mapping positioned Lp between D1Mit113 and Tagln2, an interval of ~700 kb, within which at least 12 genes had been mapped. To further aid in candidate gene identification, a bacterial clone contig was constructed, covering the region with PAC and P1 clones. Exon trapping has been carried out on 6 overlapping PAC clones spanning the majority of the critical region. Approximately 600 colonies were analysed and one or more exon was isolated for each of the previously identified genes. In addition, exons either with no known homology or with homology to previously unmapped ESTs have been identified and are currently under investigation. Candidate genes in the interval are being analysed for their expression profiles in neurulation stage embryos and comparatively sequenced to look for differences between wildtype and mutant mice. Identification of the Lp gene will enable the cloning of its human homologue and to identify a role in human NTD, further, it will provide an important model for the study of primary neurulation.