MES-4 and PRC2 regulation of gene expression in germline and soma. A. In genes normally expressed in germ cells (top), MES-4 activity is required for proper activation, and this is hypothesized to result from its antagonistic inhibition of PRC2-mediated repression. In genes normally expressed in soma (middle), PRC2 prevents MES-4 modification of these genes leading to a default repressed state. B. In somatic tissues (bottom), residual MES-4 activity marks genes for activation, but repressor complexes such as Rb and NURD (see text) normally prevent this activation in somatic lineages. MES-4 itself is also repressed in somatic lineages, presumably to reinforce this repression.