TARGETED MUTATIONS IN THE CAENORHABDITIS-ELEGANS POU HOMEO BOX GENE CEH-18 CAUSE DEFECTS IN OOCYTE CELL-CYCLE ARREST, GONAD MIGRATION, AND EPIDERMAL DIFFERENTIATION

We used targeted gene inactivation to analyze the function of a Caenor habditis elegans POU gene, ceh-18, and to dissect its functional domai ns in vivo. In ceh-18 mutants, oocytes exhibit an incompletely penetra nt failure to arrest in diakinesis of meiotic prophase I and instead u ndergo multiple rounds of DNA replication without cytokinesis. ceh-18 is expressed in the gonadal sheath cells that signal the oocyte, but n ot in the oocyte. This suggests that ceh-18 affects, directly or indir ectly, a sheath cell signal that causes oocytes to maintain diakinesis arrest. ceh-18 also participates in directing gonad migration and in specifying the differentiated phenotypes of epidermal cells during pos tembryonic development. Analysis of targeted deletions that disrupt ha lf of the POU domain selectively by deleting either the POUhd or the P OUsp alone, indicates that each CEH-18 POU subdomain is sufficient for partial activity in vivo.