ASYMMETRICALLY DISTRIBUTED PAR-3 PROTEIN CONTRIBUTES TO CELL POLARITYAND SPINDLE ALIGNMENT IN EARLY C-ELEGANS EMBRYOS

The par-3 gene is required for establishing polarity in early C. elega ns embryos. Embryos from par-3 homozygous mothers show defects in segr egation of cytoplasmic determinants and in positioning of the early cl eavage spindles. We report here that the PAR-3 protein is asymmetrical ly distributed at the periphery of the zygote and asymmetrically divid ing blastomeres of the germline lineage. The PAR-3 distribution is rou ghly the reciprocal of PAR-1, another protein required-for establishin g embryonic polarity in C. elegans. Analysis of the distribution of PA R-3 and PAR-1 in other par mutants reveals that par-2 activity is requ ired for proper localization of PAR-3 and that PAR-3 is required for p roper localization of PAR-1. In addition, the distribution of the PAR- 3 protein correlates with differences in cleavage spindle orientation and suggests a mechanism by which PAR-3 contributes to control of clea vage pattern.