Diel phasing of the cell-cycle in the Florida red tide dinoflagellate, Gymnodinium breve

The diel cycle is a key regulator of the cell-cycle in many dinoflagellates , but the mechanisms by which the diel cycle entrains the cell-cycle remain poorly understood. In this study, we describe diel phasing of the cell-cyc le in the Florida red tide dinoflagellate Gymnodinium breve Davis, determin e the diel cue which serves to entrain the cell-cycle, and provide evidence for the presence of cyclin-dependent kinase (CDK), a cell-cycle regulator which may be responsive to this cue. Four laboratory isolates from the West Coast of Florida were compared. When gown on a 16:8 h LD cycle, all isolat es displayed phased cell division, with the S-phase beginning 6-8 h into th e light phase, and mitosis following 12-14 h later, as determined by flow c ytometry, A naturally occurring bloom of G. breve, studied over one diel cy cle, displayed diel cell-cycle phasing similar to that in the laboratory cu ltures, with the S-phase beginning during daylight and the peak of mitosis occurring approximately 4 h after sunset. In the laboratory cultures, the d ark/light "dawn" transition was found to provide the diel cue which serves to entrain the G, breve cell-cycle, whereas the light/ dark "dusk" transiti on did not appear to be involved. Evidence for the presence of CDK in G. br eve was obtained using two approaches: (1) identification of a 34-kDa prote in, immunoreactive to an antibody against a conserved amino acid sequence ( alpha-PSTAIR) unique to the CDK protein family and (2) inhibition of the ce ll-cycle by olomoucine, a selective CDK inhibitor. Together, these results provide the basis from which one can begin addressing mechanisms by which t he diel cycle regulates the cell-cycle in G. breve.