Caenorhabditis elegans has four members of the Six/sine oculis class of homeobox genes,
ceh-32,
ceh-33,
ceh-34, and
ceh-35. Proteins encoded by this gene family are transcription factors sharing two conserved domains, the homeodomain 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 gonadal 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 transgenic worms is able to induce
ceh-32 ectopically. In addition, we demonstrate that VAB-3 is able to bind directly to the
ceh-32 upstream regulatory region in vitro and to activate reporter gene transcription in a yeast one-hybrid 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.