T-box genes are transcription factors, some of which are have a role in mesoderm formation and/or organisation in vertebrates (e.g. Brachyury, VegT, and Eomesodermin). We previously showed that
vab-7 is required for patterning the posterior mesoderm, and we would like to find additional genes involved. Therefore, we have begun to investigate whether any C. elegans T-box genes have a function in mesodermal patterning. There are 17 T-box homologues in the C. elegans genomic sequence. So far, we have inactivated the functions of 11 singly using RNAi. None has an embryonic lethal phenotype. However, when two divergently transcribed T-box genes (T07C4.2 and T07C4.6) are inactivated together, the resulting progeny are lethal. These embryos have grossly abnormal body morphology, with severe muscle and epidermal patterning defects. The intestine is also abnormally shortened. To ask whether these genes have a function in patterning with
vab-7 , we examined
vab-7 expression in the RNAi embryos. We found that mesodermal expression of
vab-7 is abolished, but epidermal expression is normal. The number of muscle cells is normal in these embryos, so this suggests that
vab-7 might be a target of these genes in the mesoderm. Consistent with this, there is a consensus brachyury binding site in the
vab-7 promoter. When T07C4.6 is expressed under the control of a heat shock promoter, weak ectopic
vab-7 expression is induced in some cells of early embryos (100 cell stage), but later embryos do not have ectopic
vab-7 . Therefore, T07C4.6 is not generally sufficient for
vab-7 expression, but may be sufficient in particular cells during a small time window. A T07C4.6::gfp reporter gene is first expressed in nuclei at the 28-cell stage in Ea and Ep. Later expression is in diverse cell types, including the epidermis, muscles and intestine. The pharynx and most neurons do not express the reporter gene, and expression is gone by the end of embryogenesis. The results show that T07C4.2 and T07C4.6 have overlapping mesodermal and ectodermal patterning functions, and may play a role in intestinal development as well. We are currently inactivating the remaining T-box genes, singly and in groups to find if any others also play a role in embryonic patterning.