Cyclic AMP-mediated control of meiosis: effects of progesterone, cholera toxin, and membrane-active drugs in Xenopus laevis oocytes.

Abstract

Progesterone depressed rapidly (50% at 1 min) and persistently cyclic AMP (cAMP) concentration that had been elevated by cholera toxin in Xenopus laevis oocytes. cAMP remained below 1 pmol per oocyte (mean basal level) for 1 hr and thereafter rose to =120% ofcontrol values, while germinal vesicle (nucleus) breakdown did not occur. In the absence ofcholera toxin, progesterone treatment for 6 hr maintained cAMP concentration below the basal level (but not lower than 80%), and germinal vesicle breakdown occurred. Experiments in the presence of phosphodiesterase inhibitors suggested that progesterone modulates adenylate cyclase activity. The maturation promoting factor, which is formed after 3-5 hr of progesterone treatment and provokes germinal vesicle breakdown after its injection into untreated oocytes, also decreased cAMP concentration, an observation that may explain its "autoamplification." Nonsteroidal inducers of meiosis reinitiation (e.g., propranolol, methoxyverapamil, mersalyl) diminished the cholera toxin-mediated accumulation of cAMP, in contrast to compounds devoid of meiotic-inducing capacity and antagonists to progesterone action, such as gammexane (an inositol analogue) and 5'-deoxy-S-(2-methylpropyl)-5'-thioadenosine (a methylase inhibitor), that increased the nucleotide level. The fine control, suggested by the effects of small changes in cAMP levels, gives evidence of great sensitivity to a critical determinant governing meiotic cell division.A large body ofdata suggests the involvement ofmembrane sites for progesterone and other steroidal and nonsteroidal inducers of in vitro meiosis reinitiation in Xenopus laevis (1-3). Membrane interactions are followed by intracellular events, such as Ca2" movements, nucleus-independent protein synthesis, protein phosphorylation/dephosphorylation, and the formation of a cytoplasmic "maturation-promoting factor" (MPF). MPF itself can induce meiotic cell division (maturation) in ==2-3 hr, when it is transferred into recipient oocytes that have not been exposed to progesterone (4,5).In addition, a regulatory role for cyclic AMP (cAMP) known to be implicated in the control of cell division processes (6, 7), has been suggested on the basis of two series of experiments. Purified subunits of cAMP-dependent protein kinase, isolated from rabbit muscle, have been injected into recipient oocytes (8). The catalytic subunit inhibited the progesterone-induced process, whereas the regulatory subunit directly induced cell division (as did the inhibitor ofthe catalytic subunit). Secondly, progesterone-induced reinitiation of meiosis was inhibited by cholera toxin. This observation led to experiments which suggested that cAMP is involved in the control of progesteroneinduced meiosis (9, 10). This, together with the results of MPF injected at various times into the oocytes (10), indicated a regulatory role for cAMP in MPF formation and amplification-i.e., during the 3-to 5-hr period of progesterone exposure. Measurements ofcAMP in progesterone-treated oocytes ofXenopus...

Posttranscriptional activation of gene expression in Xenopus laevis oocytes by microRNA–protein complexes (microRNPs)

“…cAMP levels increase in some G0 mammalian cells (6,7) and in immature folliculated oocytes ( Fig. S2A) (5). Maturation can be prevented by adding inhibitors of phosphodiesterases and nondegradable cAMP analogues (5).…”

“…The immature oocyte is surrounded by follicle cells that maintain high cAMP levels and downstream protein kinase A (PKA) signaling, thereby inhibiting maturation (5). Defolliculation and progesterone treatment cause a loss of signaling through G protein-coupled receptors, leading to altered PKA signaling, loss of the nuclear membrane [called germinal vesicle (GV) breakdown], and maturation (5).…”

“…The immature oocyte is surrounded by follicle cells that maintain high cAMP levels and downstream protein kinase A (PKA) signaling, thereby inhibiting maturation (5). Defolliculation and progesterone treatment cause a loss of signaling through G protein-coupled receptors, leading to altered PKA signaling, loss of the nuclear membrane [called germinal vesicle (GV) breakdown], and maturation (5). The cAMP-inducible PKA holoenzyme acts as PKAI or PKAII as a result of modulation of the catalytic subunit by alternative cofactors, repressor I (RI) or II (RII) subunits (6); both RI and RII respond to cAMP levels, with RII requiring higher levels of cAMP.…”

Expression of Histamine H1‐Receptors in Xenopus Oocytes Injected with Messenger Ribonucleic Acid from Bovine Adrenal Medulla: Pertussis Toxin Insensitive Activation of Membrane Chloride Currents

“…Evidence has been presented for the presence of G,-and Gi-like proteins in oocytes (38)(39)(40)(41) and a G,, has been cloned (42). In the case of the functional expression of cloned receptor proteins (19,25,33,(43)(44)(45), such as that for serotonin 2, the expressed receptor must be coupled to an oocyte G-protein which is apparently sensitive to PTX (Fig.…”

ARPP19 Phosphorylations by PKA and Greatwall: The Yin and the Yang of the Cell Decision to Divide

“…The drop in cAMP concentration and PKA downregulation are both necessary and sufficient for unlocking a molecular cascade that activates Cdk1 3-5 h later. Forskolin, cholera toxin and IBMX, three cAMP-elevating agents, or recombinant PKA C , are all potent inhibitors of progesterone-induced meiosis resumption [88][89][90][91]. Conversely, injection of recombinant PKA R or a specific protein inhibitor of PKA, PKI, in the oocyte is sufficient to activate Cdk1 in the absence of progesterone [92,93].…”