Dissecting the developmental and molecular defect in split hand/ split foot malformation

grantor: University of TorontoSplit hand/split foot malformation is a human developmental limb defect that affects the central rays of the hands and feet, resulting in missing digits and claw-like extremities. Commonly segregating as an autosomal dominant disorder, this genetically heterogeneous disease displays a number of distinctive genetic features including reduced penetrance, variable expressivity, and segregation distortion, where affected males transmit the disease to their male offspring in excess of 50 percent. A SHFM locus (SHFM1) has been mapped to human chromosome 7 on the basis of a large number of patients with visible cytogenetic rearrangements. A physical map spanning this region has been generated and a 1Mb SHFM1 critical interval has been defined at 7q21.3-q22.1. This thesis describes the identification and characterization of five genes from the SHFM1 critical interval. 'DSS1', the first gene identified, encodes a putative novel acidic protein and has a developmental expression profile consistent with a role in the disease process. ' DNCI1', a cytoplasmic dynein gene, is likely not involved in the basic defect but it may be implicated in the non-Mendelian segregation observed in this disease. Two homeobox transcription factors, 'DLX5' and 'DLX6', are expressed during limb development and the known function of the related gene in 'Drosophila' further implicates them in limb development. Lastly, 'DSS2', a putative mitochondrial ATP transporter, is expressed in a specific pattern during limb development highly suggestive of role in the disease process. What is more important, ' DSS2' is the only gene identified that is directly interrupted by disease associated balanced translocation breakpoints, making it an interesting candidate. In addition, a phenotypic analysis of a mouse model for SHFM, called ' Dactylaplasia', was undertaken to further understand the disease process. It was determined that the phenotype results from the failure to maintain the central portion of the apical ectodermal ridge, a key signaling centre in the developing limb bud. It is further shown that this tissue is lost due to a lack of cellular proliferation. The data presented in this thesis provide a framework from which to begin to understand the developmental and molecular defect in SHFM.Ph.D