TRICHOMONAS-VAGINALIS - DOMINANT G2 PERIOD AND G2 PHASE ARREST IN A REPRESENTATIVE OF AN EARLY BRANCHING EUKARYOTIC LINEAGE

Eukaryotic mitotic cell cycles have been extensively studied in yeasts and vertebrate cells but little is known about cell cycle mechanisms in early branches of the eukaryotic lineage. Trichomonas vaginalis rep resents one of the earliest branching eukaryotic lineages available fo r study. In contrast with most yeasts and vertebrate cells, the T. vag inalis G2 period was prolonged, comprising 50 to 58% of the cell popul ation. Hydroxyurea, aphidicolin, and excess thymidine, all of which ar rest yeasts and vertebrate cells at the G1/S phase boundary, had no ef fect on the T. vaginalis cell cycle, probably due to the known absence of synthetic pathways. The antimicrotubule mitotic inhibitors, colchi cine and nocodazole, induced G2 phase synchrony. Metronidazole, a ther apeutic reagent, also caused G2 phase arrest. These observations sugge st that T. vaginalis is similar to yeasts and vertebrate cells in G2 a nd M phases, but the parasite's G1/S phase transition is distinctive. The results also suggest potentially therapeutic, anti-trichomonad act ivity of microtubule inhibitors such as nocodazole. The cultured paras ite may prove useful as a model for the mitotic cell cycle in the abse nce of GI/S phase transitional activities universal in yeasts and vert ebrate cells.