Cell migration is an important process in animal development. The migration of gonadal distal tip cells (DTCs) offers an excellent model for migration of epithelial tubes in organogenesis.
mig-18 mutants cause meandering or wandering migration of DTCs during gonad formation and result in misshapen gonad arms. This phenotype is very similar to that observed in mutations in the
mig-17 gene encoding a secreted metalloprotease of the ADAMTS family. We cloned
mig-18 by injection rescue experiments using fosmid genomic clones.
mig-18 was found to corresponds to a predicted gene F11F1.6. The predicted protein encoded by F11F1.6 is a novel protein only well conserved in nematode species, while it is likely to be a secreted protein because of the N-terminal signal peptide and the conserved cysteine motifs. The double mutants between
mig-17(null) and
mig-18 mutants exhibited phenotypes similar to those in mg-17(null) single mutants, suggesting that
mig-18 and
mig-17 function in a common pathway. We examined the localization of MIG-17 in the gonadal basement membrane in
mig-18 mutants. MIG-17-Venus localized clearly as in the wild type background. Thus, MIG-18 is not required for gonadal localization of MIG-17. The
mig-18::Venus fusion gene was expressed in the body wall muscle cells. MIG-18-Venus appeared to be secreted from the muscle cells and localize to the gonadal basement membrane, a tissue distribution reminiscent to that observed in MIG-17.