CYCLIC-AMP IS A SIGNAL FOR REPRESSION OF DIFFERENTIATION INTO GAMETESIN MICRASTERIAS-THOMASIANA VAR NOTATA

This study investigates the effects of adenosine 3':5'-cyclic monophos phate (cAMP) and several chemicals which elevate the intracellular lev el of cAMP on the induction of zygote formation in Micrasterias thomas iana var. notata. When added at a concentration of 0.5-3 mM, cAMP repr essed the induction of zygotes and simultaneously promoted cell prolif eration, although at a concentration of 0.1 mM it merely delayed the i nitiation of zygote induction. Methylxanthines caffeine (0.05-1 mM) an d theophylline (0.05-1 mM), forskolin (10 mu M), which is a potent act ivator of adenylate cyclase, and a membrane-permeable cAMP analog, 8-b romo cAMP (0.1-3 mM), also repressed the induction of zygotes and simu ltaneously promoted cell proliferation. In contrast, another cAMP anal og used in this study, N-6,O-2'-dibutyryl cAMP (2-3 mM), repressed the induction of zygotes but did not cause promotion of cell proliferatio n. This analog also specifically blocked the cell division directly in volved with gamete formation. The results obtained suggest that intrac ellular cAMP may function as a signal which simultaneously represses z ygote induction and causes proliferation of cells in Micrasterias.