MEX-5 and MEX-6 function to establish soma/germline asymmetry in early C-elegans embryos

An asymmetrical network of cortically localized PAR proteins forms shortly after fertilization of the C. elegans egg. This network is required for sub sequent asymmetries in the expression patterns of several proteins that are encoded by nonlocalized, maternally expressed mRNAs. We provide evidence t hat two nearly identical genes, mex-5 and mex-6, link PAR asymmetry to thos e subsequent protein asymmetries. MEX-5 is a novel, cytoplasmic protein tha t is localized through PAR activities to the anterior pole of the 1-cell st age embryo. MEX-5 localization is reciprocal to that of a group of posterio r-localized proteins called germline proteins. Ectopic expression of MEX-5 is sufficient to inhibit the expression of germline proteins, suggesting th at MEX-5 functions to inhibit anterior expression of the germline proteins.