ESTROGEN DELAYS ENTRY OF THE YEAST SACCHAROMYCES-CEREVISIAE INTO MEIOSIS

Estrogen has been suggested to influence the cell cycle of haploid yeast cells in the early G1 phase of mitosis, its effect possibly being mediated by control of the level of cAMP (TANAKA, S. et al. (1989). Cell, 57: 675-681). Therefore, we were interested in whether estrogen also affects the meiotic phase of diploid yeast cells. Accordingly, we measured the amounts of adenylate cyclase mRNA and intracellular cAMP, the proportions of dividing cells and 4n cells and the doubling times of diploid yeast cells during the presporulation stage in the presence and absence of estrogen. The amount of adenylate cyclase mRNA was found to decrease rapidly within 24 hours after inoculation of cells onto sporulation-promoting plates (YPA plates). The cAMP level of these cells also decreased rapidly. Mitotic cell division continued for 18 hours after cell inoculation, but about 24 hours after inoculation, the amount of cAMP per cell had decreased to a minimum and the cells began to enter meiosis. By contrast, when the cells were inoculated onto YPA plates in the presence of estrogen, their intracellular cAMP and adenylate cyclase mRNA levels became higher than those in control cultures without estrogen and cell division continued for 24 hours. But after 30 hours their intracellular cAMP level decreased to a minimum and they began to enter meiosis. These results show that estrogen delayed the entry of diploid yeast cells into meiosis on sporulation-promoting plates and suggest that its effect may be mediated by control of the level of cAMP.