The Caenorhabditis elegans Six/sine oculis class homeobox gene ceh-32 is required for head morphogenesis

Caenorhabditis elegans has four members of the Six/sine oculis class of hom eobox genes, ceh-32, ceh-33, ceh-34, and ceh-35. Proteins encoded by this g ene family are transcription factors sharing two conserved domains, the hom eodomain and the Six/sine oculis domain, both involved in DNA binding. ceh- 32 expression was detected during embryogenesis in hypodermal and neuronal precursor cells and later in descendants of these cells as well as in gonad al sheath cells. RNAi inactivation studies suggest that ceh-32 plays a role in head morphogenesis, like vab-3, the C. elegans Pax-6 orthologue. ceh-32 and vab-3 are coexpressed in head hypodermal cells and ceh-32 mRNA levels are reduced in vab-3 mutants. Moreover, ectopic expression of VAB-3 in tran sgenic worms is able to induce ceh-32 ectopically. In addition, we demonstr ate that VAB-3 is able to bind directly to the ceh-32 upstream regulatory r egion in vitro and to activate reporter gene transcription in a yeast one-h ybrid system. Out results suggest that VAB-3 acts upstream of ceh-32 during head morphogenesis and directly induces ceh-32. Thus, ceh-32 appears to be the first target gene of VAB-3 identified so far. (C) 2001 Academic Press.