The maternal genes apx-1 and glp-1 and establishment of dorsal-ventral polarity in the early C. elegans embryo.

The sister blastomeres ABp and ABa are equipotent at the beginning of the 4-cell stage in C. elegans embryos, but soon become committed to different fates. We show that the glp-1 gene, a homolog of the Notch gene of Drosophila, functions in two distinct cell-cell interactions that specify the ABp and ABa fates. These interactions both require maternal expression of glp-1. We show that a second maternal gene, apx-1, functions with glp-1 only in the specification of the ABp fate and that apx-1 can encode a protein homologous to the Delta protein of Drosophila. Our results suggest how interactions mediated by glp-1 and apx-1 contribute to the establishment of the dorsal-ventral axis in the early C. elegans embryo.