A role for cyclin J in the rapid nuclear division cycles of early Drosophila embryogenesis

The nuclear division cycles of early Drosophila embryogenesis have a number of unique features that distinguish them from later cell cycles. These fea tures include the lack of some checkpoints that operate in later cell cycle s, the absence of gap phases, and very rapid DNA synthesis phases. The mole cular mechanisms that control these rapid nuclear division cycles are poorl y understood. Here we describe analysis of cyclin J, a previously uncharact erized cyclin which has an RNA expression pattern that suggests a possible role in early embryogenesis. We show that the cyclin J protein is present i n early embryos where it forms active kinase complexes with cyclin-dependen t kinase (Cdk) 2. To determine whether cyclin J plays a role in controlling the early nuclear cycles we isolated peptide aptamers that specifically bi nd to cyclin J and inhibit its ability to activate Cdks. We injected the in hibitory aptamers into syncytial Drosophila embryos and demonstrated that t hey caused defects in chromosome segregation and progression through mitosi s. We obtained similar results by injecting cyclin J antibodies into embryo s. Our results suggest that a cyclin J-associated kinase activity is requir ed for the early embryonic division cycles. (C) 2000 Academic Press.