Nervous system development and circuit formation requires neurons to migrate from their birthplaces to specific destinations. Migrating neurons detect extracellular cues that provide guidance information. In Caenorhabditis elegans, the QR and QL neuroblast descendants migrate long distances in opposite directions. The Hox gene
lin-39 cell-autonomously promotes anterior QR descendant migration, and
mab-5/Hox cell-autonomously promotes posterior QL descendant migration. Here we describe a non-autonomous role of
mab-5 in regulating both QR and QL descendant migrations, a role masked by redundancy with
lin-39 A third Hox gene,
egl-5/Abdominal-B, also likely non-autonomously regulates Q descendant migrations. In the
lin-39 mab-5 egl-5 triple mutant, little if any QR and QL descendant migration occurs. In addition to well-described roles of
lin-39 and
mab-5 in the Q descendants, our results suggest that
lin-39,
mab-5 and
egl-5 might also pattern the posterior region of the animal for Q descendant migration. Previous studies showed that the
spon-1 gene might be a target of MAB-5 in Q descendant migration.
spon-1 encodes a secreted basement membrane molecule similar to vertebrate F-spondin. Here we show that
spon-1 acts non-autonomously to control Q descendant migration, and might function as a permissive rather than instructive signal for cell migration. We find that increased levels of MAB-5 in body wall muscle can drive
spon-1 promoter adjacent to the Q cells, and loss of
spon-1 suppresses
mab-5 gain-of-function. Thus, MAB-5 might non-autonomously control Q descendant migrations by patterning the posterior region of the animal to which Q cells respond.
spon-1 expression from body wall muscles might be part of the posterior patterning necessary for directed Q descendant migration.