MEX-1 AND THE GENERAL PARTITIONING OF CELL FATE IN THE EARLY C-ELEGANS EMBRYO

It is thought that at least some of the initial specification of the f ive somatic founder cells of the C. elegans embryo occurs cell-autonom ously through the segregation of factors during cell divisions. It has been suggested that in embryos from mothers homozygous for mutations in the maternal-effect gene mex-1, four blastomeres of the 8-cell embr yo adopt the fate of the MS blastomere. It was proposed that mex-1 fun ctions to localise or regulate factors that determine the fate of this blastomere. Here, a detailed cell lineage analysis of 9 mex-1 mutants reveals that the fates of all somatic founder cells are affected by m utations in this gene. We propose that mex-1, like the par genes, is i nvolved in establishing the initial polarity of the embryo.