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Vincent Manganiello,
Pulmonary Critical Care Medicine Branch, NHLBI (301-496-1770 )/email: manganiv@nhlbi.nih.gov and
Manfred Boehm, Cardiology Branch, NHLBI (301-435-7211)/email: mb454z@nih.gov:
ROLE OF CYCLIC NUCLEOTIDE PHOSPHODIESTERASE 3A (PDE3A) IN OOCYTE MATURATION AND FEMALE INFERTILITY - It is known that cyclic AMP (cAMP) blocks meiotic maturation of mammalian and amphibian oocytes in vitro, and that PDE3A is primarily responsible for oocyte cAMP hydrolysis. We generated PDE3A-deficient mice by homologous recombination. PDE3A KO females were viable and ovulated normally, but were completely infertile, because their oocytes were arrested at the germinal vesicle stage, and, therefore, could not be fertilized. In a collaborative study with researchers at Stanford University Medical School, we found that PDE3A KO oocytes lacked cAMP-specific PDE activity, contained increased cAMP, and failed to undergo spontaneous maturation in vitro. Meiotic maturation in PDE3A KO oocytes was reinitiated by inhibiting protein kinase A with Rp-cAMPs (adenosine-3’,5’-cyclic-monophosphorothioate, Rp-isomer), or by injection of KO oocytes with protein kinase inhibitor peptide PKI or mRNA encoding phosphatase CDC25. These results suggested that enhanced cAMP-PKA signaling might be responsible for meiotic blockade. PDE3A KO oocytes that underwent germinal vesicle breakdown in vitro showed activation of MPF (maturation promoting factor) and MAP kinase, completed the first meiotic division, and became competent for fertilization by spermatozoa. Our more recent data, however, suggest that altered PKA activity may not be solely responsible for inhibition of maturation, but rather alteration of the subcellular localization of PKA and consequent dysregulation of phosphorylation of downstream effectors may also be important in meiotic arrest. Future studies will attempt to dissect the cAMP-signaling pathways involved in regulation of PKA translocation and meiotic maturation. We believe our findings (J. Clin. Invest. 114: 196-205, 2004) provide genetic evidence that resumption of meiosis in vitro and in vivo requires PDE3A activity. PDE3A KO mice represent an in vivo model where meiotic maturation and ovulation are dissociated, which underscores inhibition of oocyte maturation as a potential strategy for contraception.
