CELL CYCLE REGULATORS IN THE FLORIDA RED TIDE DINOFLAGELLATE, GYMNODINIUM BREVE

The diel cycle is a key regulator of the cell cycle in many dinoflagellates, and may play a rate limiting role in bloom formation. Diel phasing of the cell cycle in the Florida red tide dinoflagellate, Gymnodinium breve Davis was previously described in our laboratory. In cultures grown on a 16:8 light:dark cycle, S‐phase began 6–8 h into the light phase, and mitosis followed 12–14 h later. The dark/light “dawn” transition was found to provide the diel cue that serves to entrain the G. breve cell cycle. However the cell cycle mechanisms and regulators acted upon by this cue are poorly understood in dinoflagellates. The cell cycle regulatory complex, CDK1‐cyclinB, is therefore currently being investigated. Cyclin dependent kinase (CDK) was first identified in G. breve using two approaches: (1) identification of a 34 kDa protein immunoreactive to an antibody raised against a conserved amino acid sequence unique to the CDK protein family (PSTAIR) and (2) inhibition of the cell cycle by olomoucine, a selective CDK inhibitor. Several approaches are currently being employed in order to describe its partner, cyclin B: (1) PCR on genomic DNA with primers deduced from known cyclin box sequences, (2) G. breve expression library screening with an antibody raised against the fission yeast cyclin B (3) western blot analysis on whole protein extracts and cyclin B immunoprecipitated proteins. Current work focuses on the differential expression of the cyclin B homologue in G. breve during its cell cycle and its relation to diel cycle control.