Search

Blastomeres in C. elegans embryos execute lineage programs wherein the fate of a cell is correlated reproducibly with the division sequence by which that cell is born. We provide evidence that the pop-1 gene functions to link anterior-posterior cell divisions with cell fate decisions. Each anterior cell resulting from an anterior-posterior division appears to have a higher level of nuclear POP-1 protein than does its posterior sister. Genes in the C. elegans Wnt pathway are required for this inequality in POP-1 levels. We show that loss of pop-1(+) activity leads to several types of anterior cells adopting the fates of their posterior sisters. These results suggest a mechanism for the invariance of blastomere lineages.

The par-3 gene is required for establishing polarity in early C. elegans embryos. Embryos from par-3 homozygous mothers show defects in segregation of cytoplasmic determinants and in positioning of the early cleavage spindles. We report here that the PAR-3 protein is asymmetrically distributed at the periphery of the zygote and asymmetrically dividing blastomeres of the germline lineage. The PAR-3 distribution is roughly the reciprocal of PAR-1, another protein required for establishing embryonic polarity in C. elegans. Analysis of the distribution of PAR-3 and PAR-1 in other par mutants reveals that par-2 activity is required for proper localization of PAR-3 and that PAR-3 is required for proper 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 cleavage pattern.