CELL-CYCLE MUTATION IN PARAMECIUM-TETRAURELIA DISCRIMINATES BETWEEN SEXUAL AND VEGETATIVE FUNCTIONS

The temperature-sensitive mutation cc1 blocks a number of cell cycle p rocesses in Paramecium including macronuclear DNA synthesis, oral morp hogenesis, and the later stages of micronuclear mitosis. Oral morphoge nesis and micronuclear mitosis also occur in the sexual pathway. This study shows that cc1 cells can proceed through conjugation or autogamy under restrictive conditions; neither stomatogenesis nor micronuclear mitosis is blocked. Fertilization and macronuclear determination occu r normally, but DNA synthesis in macronuclear anlagen is blocked. Ther efore, this mutation discriminates between oral replacement during mei osis and vegetative prefission stomatogenesis, and between mitotic spi ndle elongation during the pregamic and postzygotic divisions and spin dle elongation during the vegetative cell cycle. These results point t o a fundamental regulatory difference between morphogenesis in the veg etative and sexual pathways. (C) 1994 Wiley-Liss, Inc.