Abstract
Background In mammalian ovarian follicles, granulosa cells keep fully grown oocytes arrested in meiotic prophase. A key inhibitory signal is cGMP, which diffuses into the oocyte from the granulosa cells, where it is synthesized by guanylyl cyclase B/ natriuretic peptide receptor 2 (NPR2) in response to the agonist C-type natriuretic peptide (CNP) [1]. Then in response to luteinizing hormone (LH), cGMP in the granulosa cells and oocyte decreases, promoting resumption of meiosis [2]. The primary mechanism by which LH signaling reduces cGMP in the granulosa cells is by reducing the activity of NPR2; this occurs by a rapid modification of the NPR2 protein, followed by a decrease in CNP in the ovary [3].
Highlights
BackgroundGranulosa cells keep fully grown oocytes arrested in meiotic prophase
In mammalian ovarian follicles, granulosa cells keep fully grown oocytes arrested in meiotic prophase
The decrease in guanylyl cyclase activity measured at 20 minutes after luteinizing hormone (LH) application was inhibited by preincubating the follicles with the phosphatase inhibitor okadaic acid, suggesting that LH signaling decreases natriuretic peptide receptor 2 (NPR2) activity by dephosphorylating the protein
Summary
Granulosa cells keep fully grown oocytes arrested in meiotic prophase. A key inhibitory signal is cGMP, which diffuses into the oocyte from the granulosa cells, where it is synthesized by guanylyl cyclase B/ natriuretic peptide receptor 2 (NPR2) in response to the agonist C-type natriuretic peptide (CNP) [1]. To determine if dephosphorylation occurred, we immunoprecipitated NPR2 from rat follicle membranes, and separated phosphorylated forms of NPR2 using 6% polyacrylamide gels containing 25 μM Mn2 +-Phos-tag-acrylamide, which retards the migration of phosphorylated proteins [8]. Immunoblotting of these gels showed that a 20 minute treatment of the follicles with LH reduced the amount of the more slowly migrating species of NPR2, which is consistent with dephosphorylation
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