PAR-6, A GENE INVOLVED IN THE ESTABLISHMENT OF ASYMMETRY IN EARLY CAENORHABDITIS-ELEGANS EMBRYOS, MEDIATES THE ASYMMETRIC LOCALIZATION OF PAR-3

The generation of asymmetry in the one-cell embryo of Caenorhabditis e legans is necessary to establish the anterior-posterior axis and to en sure the proper identity of early blastomeres. Maternal-effect lethal mutations with a partitioning defective phenotype (pal) have identifie d several genes involved in this process. We have identified a new gen e, par-6, which acts in conjunction with other par genes to properly l ocalize cytoplasmic components in the early embryo. The early phenotyp es of par-6 embryos include the generation of equal-sized blastomeres, improper localization of P granules and SKN-1 protein, and abnormal s econd division cleavage patterns. Overall, this phenotype is very simi lar to that caused by mutations in a previously described gene, par-3. The probable basis for this similarity is revealed by our genetic and immunolocalization results; par-6 acts through par-3 by localizing or maintaining the PAR-3 protein at the cell periphery. In addition, we find that loss-of-function par-6 mutations act as dominant bypass supp ressors of loss-of-function mutations in par-2.