T-box genes form a large family of conserved transcription factors with diverse roles in animal development, but so far functions for only a few have been studied in detail. Here we show that four Caenorhabditis elegans T-box genes and the even-skipped-like homeobox gene
vab-7 function within a regulatory network to control embryonic patterning and morphogenesis.
tbx-8 and
tbx-9 have functionally redundant roles in the intercalation of posterior dorsal hypodermal cells, in muscle cell positioning and in intestinal development. Inhibiting
tbx-9 alone using RNA interference (RNAi) produces worms that have a thickened, 'bobbed tail' phenotype, similar to that seen in mutants of
vab-7, which itself has been shown to pattern posterior muscle and hypodermal cells. In support of the view that these genes function in the same pathway, we find that
tbx-8 and
tbx-9 are both necessary and sufficient for
vab-7 expression. In addition, a third T-box gene,
tbx-30, acts to repress
vab-7 expression in the anterior of embryos. We further show that
vab-7 itself represses the T-box gene
mab-9 in posterior cells. Thus, during posterior patterning in C. elegans, there are multiple interactions between T-box genes and the
vab-7 homeobox gene. Evolutionary parallels in other organisms suggest that regulatory interactions between T-box genes and even-skipped homologues are conserved.