Drosophila wee1 has an essential role in the nuclear divisions of early embryogenesis

In Drosophila, the maternally expressed mei-41 and grp genes are required f or successful execution of the nuclear division cycles of early embryogenes is. In fission yeast, genes encoding similar kinases (rad3 and chk1, respec tively) are components of a cell cycle checkpoint that delays mitosis by in hibitory phosphorylation of Cdk1. We have identified mutations in a gene en coding a Cdk1 inhibitory kinase, Drosophila wee1 (Dwee1). Like mei-41 and g rp, Dwee1 is zygotically dispensable but is required maternally for complet ing the embryonic nuclear cycles. The arrest phenotype of Dwee1 mutants, as well as genetic interactions between Dwee1, grp, and mei-41 mutations, sug gest that Dwee1 is functioning in the same regulatory pathway as these gene s. These findings imply that inhibitory phosphorylation of Cdk1 by Dwee1 is required for proper regulation of the early syncytial cycles of embryogene sis.