A New Class of C. elegans synMuv Genes Implicates a Tip60/NuA4-like HAT Complex as a Negative Regulator of Ras Signaling

The class A and class B synMuv genes are functionally redundant negative regulators of a Ras signaling pathway that induces C. elegans vulval development. A number of class B synMuv genes encode components of an Rb and histone deacetylase complex that likely acts to repress transcription of genes required for vulval induction. We discovered a new class of synMuv genes that acts redundantly with both the A and B classes of genes in vulval cell-fate determination. These new class C synMuv genes encode TRRAP, MYST family histone acetyltransferase, and Enhancer of Polycomb homologs, which form a putative C. elegans Tip60/NuA4-like histone acetyltransferase complex. A fourth gene with partial class C synMuv properties encodes a homolog of the mammalian SWI/SNF family ATPase p400. Our findings indicate that the coordinated action of two chromatin-modifying complexes, one with histone deacetylase and the other with histone acetyltransferase activity, is important in regulating Ras signaling and specifying cell fates during C. elegans development.