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Dual roles of PDE9a in meiotic maturation of zebrafish oocytes. Li J et al. (2020) The essential role of cyclic guanosine monophosphate (cGMP) signaling in regulating the oocyte meiotic cell cycle has been established. However, control of the level of cGMP in ovarian follicles is unclear. The cGMP-hydrolyzing phosphodiesterases (PDEs) are important in regulating the cellular cGMP level. We used zebrafish as a model to study the role of a cGMP-hydrolyzing phosphodiesterase-9a (PDE9a) in meiotic maturation of oocytes. Three PDE9a coding genes (PDE9aa, PDE9ab, and PDE9ac) were identified in zebrafish. Both pde9aa and pde9ac are expressed in most adult tissues including the ovary, but pde9ab is only expressed in the ovary, kidney, pituitary, and brain. All three pde9as mRNA exhibited different expression profiles during folliculogenesis. All of them are highly expressed in the oocyte but not in the follicular cell. The expression of both pde9aa and pde9ab, but not pde9ac, in ovarian follicles increases during oocyte maturation either in natural ovulatory cycle or induced by administration of hCG in vivo. We overexpressed pde9aa by injection of capped pde9aa mRNA into the oocytes. The cGMP level was decreased, and oocyte maturation was stimulated. When the activity of PDE9a was blocked by a specific inhibitor, Bay736691, the oocyte maturation was also stimulated. The stimulatory effect could be blocked by a gap junction blocker. However, the spontaneous oocyte maturation of denuded oocytes was not largely affected after treatment with Bay736691. All of the mature oocytes obtained by either treatment of Bay736691 or injection of pde9aa mRNA, could be fertilized in vitro. These results demonstrate the dual roles of PDE9a in oocyte maturation. The basal level of PDE9a is responsible for maintaining the meiotic arrest, and the increased level of PDE9a induced by LH signaling is helpful for stimulating meiotic maturation by hydrolyzing cGMP in oocytes.//////////////////Identification of phosphodiesterase 9A as a cyclic guanosine monophosphate-specific phosphodiesterase in germinal vesicle oocytes: a proposed role inthe resumption of meiosis. Hanna CB et al. OBJECTIVE: To identify a cyclic guanosine monophosphate (cGMP)-specific phosphodiesterase (PDE) in nonhuman primate germinal vesicle (GV) oocytes and establish a proposed effect on oocyte maturation through preliminary experiments in mouse GV oocytes. DESIGN: Controlled nonhuman primate and rodent experiments. SETTING: Academic research institution. ANIMAL(S): Rhesus macaques and B6/129F1 mice. INTERVENTION(S): Stimulation of Rhesus macaques with follicle-stimulating hormone (FSH) to collect GV oocytes and cumulus for gene expression analysis, and stimulation of female mice with pregnant mare serum gonadotropin to collect GV oocytes. MAIN OUTCOME MEASURE(S): Expression of PDE transcript in primate GV oocytes and cumulus cells, measurement of fluorescence polarization of phosphodiesterase 3A (PDE3A) activity, and analysis of spontaneous resumption of meiosis in mouse GV oocytes. RESULT(S): Of five PDE transcripts detected in Rhesus GV oocytes, only PDE9A was cGMP-specific. The fluorescence polarization assays indicated cGMP has an inhibitory effect on PDE3A while the phosphodiesterase 9A (PDE9) inhibitor, BAY73-6691, does not. Similarly, BAY73-6691 had little effect on preventing spontaneous maturation in oocytes, but did augment the inhibitory effects of cGMP. Inclusion of 0 M (control), 10 M, 100 M, and 1 mM BAY73-6691 statistically significantly increased the proportion of mouse oocytes maintaining GV arrest in the presence of the cGMP analog 8-Br-cGMP at 100 M (8.8%, 11.4%, 18.8%, and 28%), 500 M (21.1%, 38.1%, 74.5%, and 66.5%), and 1 mM (57.8%, 74.5%, 93.9%, and 94.0%), respectively. CONCLUSION(S): Phosphodiesterase 9A (PDE9A) is a cGMP-specific hydrolyzing enzyme present in primate oocytes, and PDE9 antagonists augment the inhibitory effect of cGMP during spontaneous invitro maturation of GV mouse oocytes.
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