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 d ifferent fates. We show that the glp-1 gene, a homolog of the Notch ge ne of Drosophila, functions in two distinct cell-cell interactions tha t specify the ABp and ABa fates. These interactions both require mater nal expression of glp-1. We show that a second maternal gene, apx-1, f unctions 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 Drosoph ila. Our results suggest how interactions mediated by glp-1 and apx-1 contribute to the establishment of the dorsal-ventral axis in the earl y C. elegans embryo.