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Francois J. Richard1 , Alex Tsafriri2 *, Marco Conti1 *
Division of Reproductive Biology, Department of Gynecology and Obstetrics, Stanford University, School of Medicine, Stanford, CA 94305 1
Weizmann Institute of Science, Department of Biological Regulation, Bernhard Zondek Hormone Research Laboratory, Rehovot 76100 Israel 2
Cyclic AMP is a key second messenger regulating oocyte maturation. In most species studied, a decrease in intraoocyte cAMP level precedes the resumption of meiosis. Since cyclic nucleotide phosphodiesterases (PDE) are the enzymes that degrade cAMP, the goal of this study was to determine the properties and the regulation of the PDE expressed in rat oocytes. Cumulus-oocyte complexes (COCs) and follicle-enclosed oocytes (FEOs) were collected from 25-day-old Sprague-Dawley rats treated with PMSG for 48 h. The PDE activity was measured after homogenization using form-specific inhibitors. In COCs, both PDE3 (3.5 ± 0.1 fmoles/min/oocyte) and PDE4 (3.7 ± 0.2) activities were detected. When cumulus cells were removed, PDE3 was the major activity measured in the oocyte. The oocyte PDE3 was quantitatively immunoprecipitated with a PDE3A-selective antibody. To investigate the regulation of oocyte PDE3A its activity was measured after spontaneous or induced maturation. In isolated COCs, 10% of oocytes had spontaneously resumed meiosis after 30 min of culture, and by 90 min meiotic resumption had taken place in most of the oocytes (90%). A transient but significant increase (P<0.05) in PDE3 activity was measured in the oocytes after 30 min of culture (5.4 ± 1.2 fmoles/min/oocyte) compared to immediately after collection (2.3 ± 0.7). After 60 min, the activity returned to basal level. When FEOs were cultured for 2 h, hCG treatment produced a large increase in PDE3 activity (4.6 ± 0.9 vs. 1.5 ± 0.3 fmoles/min/oocyte). These data show that PDE3A is the major PDE form in mammalian oocytes and is activated prior to the resumption of meiosis during both spontaneous and induced maturation, strongly supporting the hypothesis that an activation of oocyte PDE3A is one of the intraoocyte mechanisms leading to the resumption of meiosis in rat oocytes.
This abstract is being presented on Sunday, August 1 at 8:00 AM to 10:15 AM at CUB 2nd Floor Ballroom.