MUSCLE AND NERVE-SPECIFIC REGULATION OF A NOVEL NK-2 CLASS HOMEODOMAIN FACTOR IN CAENORHABDITIS-ELEGANS

We have identified a new Caenorhabditis elegans NK-2 class homeobox ge ne, designated ceh-24. Distinct cis-acting elements generate a complex neuronal and mesodermal expression pattern, A promoter-proximal enhan cer mediates expression in a single pharyngeal muscle, the donut-shape d m8 cell at the posterior end of the pharynx, A second mesodermal enh ancer is active in a set of eight nonstriated vulval muscles used in e gg laying. Activation in the egg laying muscles requires an 'NdE-box' consensus motif (CATATG) which is related to, but distinct from, the s tandard E-box motif bound by the MyoD family of transcriptional activa tors. Ectodermal expression of ceh-24 is limited to a subset of sublat eral motor neurons in the head of the animal; this activity requires a cis-acting activator element that is distinct from the control elemen ts for pharyngeal and vulval muscle expression, Activation of ceh-24 i n each of the three cell types coincides with the onset of differentia tion. Using a set of transposon-induced null mutations, we show that c eh-24 is not essential for the formation of any of these cells. Althou gh ceh-24 mutants have no evident defects under laboratory conditions, the pattern of ceh-24 activity is apparently important for Rhabditid nematodes: the related species C, briggsae contains a close homologue of C, elegans ceh-24 including a highly conserved and functionally equ ivalent set of cis-acting control signals.