In
mig-5 mutants, various phenotypic defects related to cell migration and cell fate determination have been observed. For example, one or two DTCs are often missing, and occasionally an extra DTC is present. Some DTCs migrate irregularly, such as making precocious dorsal turns. The descendants of the QL neuroblast migrate anteriorly rather than posteriorly. In the vulval equivalence group, some vulval precursor cells are often missing, resulting in a asymatric vulval or min vulval. In the preanal equivalence group, the P12 cell often adopts a P11 cell fate. The
mig-5 gene has been positionally cloned on chromosome II. Sequence analysis indicates that
mig-5 is a homologue of dsh which is in the wingless signal transduction pathway. The
mig-5 gene is about 4 kb with nine exons. It has, at least, two different transcripts as indicated by its cDNAs. The MIG-5 protein contains three conserved domains including a PDZ domain. Two other C. elegans homologues of dsh , C27A2.6 and C34F11.9b, have been found in C. elegans by the sequencing project, which have high homology with
mig-5 especially in the PDZ domain. The PDZ domain is also found in other proteins. In those protein, PDZ domain(s) interact with receptors or channels, and provide a bridge to the intracellular signaling pathways or the cytoskeleton. The
mig-5 gene is maternally and zygotically sufficient. Between two
mig-5 alleles,
rh147 is a stronger allele containing a nonsense mutation in the PDZ domain. This mutation, together with the results from genetic tests and RNAi tests, suggests that
rh147 might be a null allele. In another allele,
rh94, a point mutation changes a splice donor site, resulting in a premature stop codon in the PDZ domain. As indicated by MIG-5::GFP transgenic animals,
mig-5 is expressed extensively in embryos and selectively in adults. For example, expression is observed in the migrating DTCs, P cells, and, interestingly, in nervous system. The expression pattern suggests that the role of
mig-5 may not only limited in the wingless signal transduction pathway. Currently, our interest is focused on further characterization of
mig-5 expression, and its genetic and physical interaction with other genes.