Rapid method for cell cycle analysis in a predatory marine dinoflagellate

Oxyrrhis marina (Dujardin) is a predatory marine dinoflagellate that feeds phagocytically on live phytoplanktonic "prey" cells from the surrounding environment. A rapid method was developed to separate the cell cycle characteristics of these predators from their prey cells in order to study the cell cycle dynamics of this organism. Nuclei from Oxyrrhis were isolated in low salt buffer (PBS) using detergent and mechanical agitation and the DNA stained with Hoechst 33258 in a one step procedure. The method permitted the isolation of nuclei from the Oxyrrhis cells with > 95% efficiency. Discrimination between prey cell nuclei and those of Oxyrrhis was achieved during flow cytometric analysis which yielded routinely G1 CVs of 3-6% for exponentially growing cell populations and 2-3% for stationary phase cells. The method was used to demonstrate the changes in cell cycle dynamics during the exponential and stationary phases of growth. Results indicated that in contrast to most mammalian and phytoplankton cell types Oxyrrhis spent the major portion (ca. 50%) of its cell cycle in G2 + M when actively dividing. Analysis of stationary phase populations also suggests that specific cell cycle control (or restriction) points were present in both G1 and G2 in this species.