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Rodent oocytes express an active adenylyl cyclase required for meiotic arrest
Kathleen Horner1, Gabriel Livera, Mary Hinckley
1Division of Reproductive Biology, Department of Obstetrics and Gynecology, Stanford University, Stanford, CA 94305, USA.
Abstract:
The intracellular levels of cAMP play a critical role in the meiotic arrest of mammalian oocytes. However, it is debated whether this second messenger is produced endogenously by the oocytes or is maintained at levels inhibitory to meiotic resumption via diffusion from somatic cells. Here, we demonstrate that adenylyl cyclase genes and corresponding proteins are expressed in rodent oocytes. The mRNA coding for the AC3 isoform of adenylyl cyclase was detected in rat and mouse oocytes by RT-PCR and by in situ hybridization. The expression of AC3 protein was confirmed by immunocytochemistry and immunofluorescence analysis in oocytes in situ. Cyclic AMP accumulation in denuded oocytes was increased by incubation with forskolin, and this stimulation was abolished by increasing intraoocyte Ca(2+) with the ionophore A23187. The Ca(2+) effects were reversed by an inhibitor of Ca(2+), calmodulin-dependent kinase II. These regulations of cAMP levels indicate that the major cyclase that produces cAMP in the rat oocyte has properties identical to those of recombinant or endogenous AC3 expressed in somatic cells. Furthermore, mouse oocytes deficient in AC3 show signs of a defect in meiotic arrest in vivo and accelerated spontaneous maturation in vitro. Collectively, these data provide evidence that an adenylyl cyclase is functional in rodent oocytes and that its activity is involved in the control of oocyte meiotic arrest.
Insights
Rodent oocytes produce cyclic AMP (cAMP) via adenylyl cyclase 3 (AC3), crucial for maintaining meiotic arrest. AC3 deficiency impairs this arrest, highlighting its role in oocyte maturation control.
Area of Science:
- Cell Biology
- Reproductive Biology
- Molecular Endocrinology
Background:
- Intracellular cyclic AMP (cAMP) levels are vital for mammalian oocyte meiotic arrest.
- A key debate exists on whether oocytes produce cAMP endogenously or if it diffuses from surrounding somatic cells.
Purpose of the Study:
- To investigate the presence and function of adenylyl cyclase (AC) in rodent oocytes.
- To determine if AC activity is involved in regulating oocyte meiotic arrest.
Main Methods:
- RT-PCR and in situ hybridization to detect adenylyl cyclase 3 (AC3) mRNA in rat and mouse oocytes.
- Immunocytochemistry and immunofluorescence to confirm AC3 protein expression.
- Forskolin stimulation and calcium ionophore (A23187) treatment to assess cAMP regulation in denuded oocytes.
- Analysis of meiotic arrest in AC3-deficient mouse oocytes.
Main Results:
- AC3 mRNA and protein are expressed in rodent oocytes.
- Forskolin increased cAMP levels, which was inhibited by increased intracellular calcium (Ca2+).
- AC3-deficient mouse oocytes exhibited impaired meiotic arrest in vivo and premature maturation in vitro.
Conclusions:
- Rodent oocytes possess functional adenylyl cyclase, specifically AC3.
- Oocyte-derived AC3 activity plays a significant role in maintaining meiotic arrest.
- These findings clarify the endogenous regulation of cAMP in oocytes and its impact on meiotic control.