Caenorhabditis elegans T‐box genes tbx‐9 and tbx‐8 are required for formation of hypodermis and body‐wall muscle in embryogenesis

Transcription factors containing the DNA binding motif, T‐box, play an important role in the embryonic development of metazoans. There are 20 T‐box genes in the nematode Caenorhabditis elegans , three of which reportedly have postembryonic functions. We characterized two T‐box genes, tbx‐9 and tbx‐8 , that are phylogenetically related to each other. tbx‐9 is expressed in a subset of embryonic cells that are precursors of the intestine, body‐wall muscle, and hypodermis. The expression pattern of tbx‐8 is markedly similar to that of tbx‐9 . Both tbx‐9 mutants and tbx‐8 mutants show incomplete penetrant morphogenetic defects in embryogenesis, but the malformations of the tbx‐9 and tbx‐8 mutants are observed in different parts of their bodies. In embryos with both tbx‐9 and tbx‐8 inactivated, the body structure is severely disorganized, more so than the sum of the separate mutant phenotypes. Further analysis shows that the hypodermis and body‐wall muscle show abnormalities at the site of morphogenetic defects of these mutants. Together, these data indicate that tbx‐9 and tbx‐8 do not only contribute individually to formation of the hypodermis and body‐wall muscle, but also suggests functional redundancy between tbx‐9 and tbx‐8 in embryonic morphogenesis.