The effect of the CCI mutation on cell cycle morphogenesis in Paramecium Tetraurelia

The ccl mutant is temperature sensitive and arrests the cell cycle at 34.4° C. The transition point for division under restrictive conditions defines the point of commitment to division. We have examined the point of commitment to division in relation to the time course of stomatogenesis and micronuclear mitosis in both synchronous and asynchronous cell samples. Our analysis shows that stomatogenesis begins well before the point of commitment to division, which occurs at the 6-rowed oral primordium stage. At this stage micronuclei are in late anaphase. Oral morphogenesis is arrested up to this stage in mutant cells at the restrictive temperature, as are later stages of micronuclear division. These results are interesting because they suggest that micronuclear DNA synthesis and initiation of mitosis occur normally in ccl mutants, even though macronuclear DNA synthesis stops immediately on transfer to restrictive conditions. The meiotic cell cycles do not require the ccl function. This suggests that ccl is required exclusively for the vegetative cell cycle and not for micronuclear division or stomatogenesis during the sexual pathways.Science, Faculty ofZoology, Department ofGraduat