The maternal gene skn-1 encodes a protein that is distributed unequally in early C. elegans embryos.

The autonomous or cell-intrinsic developmental properties of early embryonic blastomeres in nematodes are thought to result from the action of maternally provided determinants. After the first cleavage of the C. elegans embryo, only the posterior blastomere, P1, has a cell-intrinsic ability to produce pharyngeal cells. The product of the maternal gene skn-1 is required for P1 to produce pharyngeal cells. We show here that the Skn-1 protein is nuclear localized and that P1 appears to accumulate markedly higher levels of Skn-1 protein than its sister, the AB blastomere. We have examined the distribution of Skn-1 protein in embryos from mothers with maternal-effect mutations in the genes mex-1, par-1, and pie-1. These results suggest that mex-1(+) and par-1(+) activities are required for the unequal distribution of the Skn-1 protein and that pie-1(+) activity may function to regulate the activity of Skn-1 protein in the descendants of the posterior blastomere P1.