Both MEX-5 and MEX-6 proteins are highly enriched in AB after the first mitotic division, and localize to all three somatic blastomeres, but not P2, in the 4-cell embryo. In
mex-5(RNAi);
mex-6(RNAi) embryos, we observed uniform expression of GFP::H2Bmom-2 in all blastomeres as early as the 4-cell stage. The spatial localization of MEX-5/6, the derepression of GFP::H2Bmom-2 in
mex-5/6(RNAi) embryos, and the in vitro binding of the
mom-2 3'UTR by MEX-5, all suggest that MEX-5/6 directly repress translation of gfp::
h2bmom-2 mRNA in somatic blastomeres. MEX-5/6 activity is not required for gfp::
h2bmom-2 translational repression until the 4-cell stage.