NEURONAL CELL-MIGRATION IN CAENORHABDITIS-ELEGANS - REGULATION OF HOXGENE-EXPRESSION AND CELL POSITION

In C, elegans, the Hox gene mab-5, which specifies the fates of cells in the posterior body region, has been shown to direct the migrations of certain cells within its domain of function, mab-5 expression switc hes on in the neuroblast QL as it migrates into the posterior body reg ion, mab-5 activity is then required for the descendants of QL to migr ate to posterior rather than anterior positions. What information acti vates Hox gene expression during this cell migration? How are these ce lls subsequently guided to their final positions? We address these que stions by describing four genes, egl-20, mig-14, mig-1 and lin-17, tha t are required to activate expression of mab-5 during migration of the QL neuroblast. We find that two of these genes, egl-20 and mig-14, al so act in a mab-5-independent way to determine the final stopping poin ts of the migrating Q descendants. The Q descendants do not migrate to ward any obvious physical targets in wild-type or mutant animals. Ther efore, these genes appear to be part of a system that positions the mi grating Q descendants along the anteroposterior axis.