Activation of a C. elegans Antennapedia homologue in migrating cells controls their direction of migration

ANTERIOR–POSTERIOR patterning in insects, vertebrates and nematodes involves members of conserved Antennapedia -class homeobox gene clusters (HOM-C) that are thought to give specific body regions their identities 1–5 . The effects of these genes on region-specific body structures have been described extensively, particularly in Drosophila , but little is known about how HOM-C genes affect the behaviours of cells that migrate into their domains of function. In Caenorhabditis elegans , the Antennapedia -like HOM-C gene mab-5 not only specifies postembryonic fates of cells in a posterior body region, but also influences the migration of mesodermal and neural cells that move through this region 5–7 . Here we show that as one neuroblast migrates into this posterior region, it switches on mab-5 gene expression; mab-5 then acts as a developmental switch to control the migratory behaviour of the neuroblast descendants. HOM-C genes can therefore not only direct region-specific patterns of cell division and differentiation, but can also act within migrating cells to programme region-specific migratory behaviour.