ISOLATION OF DROSOPHILA CYCLIN-D, A PROTEIN EXPRESSED IN THE MORPHOGENETIC FURROW BEFORE ENTRY INTO S-PHASE

During Drosophila development, nuclear and cell divisions are coordina ted in response to developmental signals. In yeast and mammalian cells , signals that control cell division regulate the activity of cyclin-d ependent kinases (Cdks) through proteins such as cyclins that interact with the Cdks. Here we describe two Drosophila cyclins identified fro m a set of Cdk-interacting proteins. One, cyclin J, is of a distinctiv e sequence type; its exclusive maternal expression pattern suggests th at it may regulate oogenesis or the early nuclear divisions of embryog enesis. The other belongs to the D class of cyclins, previously identi fied in mammalian cells. We show that Drosophila cyclin D is expressed in early embryos and in imaginal disc cells in a pattern that anticip ates cell divisions. Expression in the developing eye disc at the ante rior edge of the morphogenetic furrow suggests that cyclin D acts earl y, prior to cyclin E, in inducing G(1)-arrested cells to enter S phase . Our results also suggest that, although cyclin D may be necessary, i ts expression alone is not sufficient to initiate the events leading t o S phase.