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 switches on in the neuroblast QL as it migrates into the posterior body region.
mab-5 activity is then required for the descendants of QL to migrate to posterior rather than anterior positions. What information activates Hox gene expression during this cell migration? How are these cells subsequently guided to their final positions? We address these questions by describing four genes,
egl-20,
mig-14,
mig-1 and
lin-17, that 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, also act in a
mab-5-independent way to determine the final stopping points of the migrating Q descendants. The Q descendants do not migrate toward any obvious physical targets in wild-type or mutant animals. Therefore, these genes appear to be part of a system that positions the migrating Q descendants along the anteroposterior axis.