Regulation of the Caenorhabditis elegans posterior Hox gene egl-5 by microRNA and the polycomb-like gene sop-2

In Caenorhabditis elegans, the domains of Hox gene expression are controlled by the novel global regulatory gene sop-2. We identified a region located 3′ of the Hox gene egl-5 that promotes ectopic expression of an egl-5 reporter gene in a sop-2 mutant. SOP-2 could directly block positive regulatory factors acting in this region, or it could block their expression. We identified three possible miRNA binding sites within the egl-5 3′ untranslated region (UTR). Cognate microRNAs are expressed in relevant tissues and can block egl-5 expression when expressed from a transgene. Mutation of the putative binding sites in the egl-5 3′UTR resulted in a modest degree of misexpression of a minimal egl-5 reporter gene, suggesting that microRNAs may contribute to the tight restriction of egl-5 expression to particular cell lineages.