The specification of body pattern along the anteroposterior (A/P) body axis is achieved largely by the actions of conserved clusters of Hox genes. Limiting expression of these genes to localized regional domains and controlling the precise patterns of expression within those domains is critically important for normal patterning. Here we report that
egl-20, a C. elegans gene required to activate expression of the Hox gene
mab-5 in the migratory neuroblast QL, encodes a member of the Wnt family of secreted glycoproteins. We have found that a second Wnt pathway gene,
bar-1, which encodes a beta-catenin/Armadillo-like protein, is also required for activation of
mab-5 expression in QL. In addition, we describe the gene
pry-1, which is required to limit expression of the Hox genes
lin-39,
mab-5 and
egl-5 to their correct local domains. We find that
egl-20,
pry-1 and
bar-1 all function in a linear genetic pathway with conserved Wnt signaling components, suggesting that a conserved Wnt pathway activates expression of
mab-5 in the migratory neuroblast QL. Moreover, we find that members of this Wnt signaling system play a major role in both the general and fine-scale control of Hox gene expression in other cell types along the A/P axis.