Cyclic AMP is a signal for repression of differentiation into gametes in Micrasterias thomasiana var. notata

Abstract This study investigates the effects of adenosine 3′:5′-cyclic monophosphate (cAMP) and several chemicals which elevate the intracellular level of cAMP on the induction of zygote formation in Micrasterias thomasiana var. notata . When added at a concentration of 0.5–3 mM, cAMP repressed the induction of zygotes and simultaneously promoted cell proliferation, although at a concentration of 0.1 mM it merely delayed the initiation of zygote induction. Methylxanthines caffeine (0.05–1 mM) and theophylline (0.05–1 mM), forskolin (10 μM), which is a potent activator of adenylate cyclase, and a membrane-permeable cAMP analog, 8-bromo cAMP (0.1–3 mM), also repressed the induction of zygotes and simultaneously promoted cell proliferation. In contrast, another cAMP analog 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 proliferation. This analog also specifically blocked the cell division directly involved with gamete formation. The results obtained suggest that intracellular cAMP may function as a signal which simultaneously represses zygote induction and causes proliferation of cells in Micrasterias .