PRE-CONJUGANT CELL-INTERACTION AND CELL-CYCLE IN THE CILIATE EUPLOTES-CRASSUS - SWITCHING FROM THE VEGETATIVE TO THE SEXUAL STAGE

Cells of Euplotes crassus can mate during the entire extent of G1 as well in the very early macronuclear S phase. An arrest to cell cycling that occurs during mating is triggered by the ciliary agglutination that takes place between complementary cells, after a waiting period and before the cell bodies fuse into conjugal pairs. Cycling arrest is reversible. Sexually developing cells returned to nutrient conditions are able to reinitiate macronuclear DNA synthesis, although after a lag period. The synchronous reinitiation of synthesis is interpreted as a consequence of reprogramming events that occur as cells switch from the vegetative to the sexual stage of the life cycle. © 1979.