Prophase I Arrest of Mouse Oocytes Mediated by Natriuretic Peptide Precursor C Requires GJA1 (connexin-43) and GJA4 (connexin-37) Gap Junctions in the Antral Follicle and Cumulus-Oocyte Complex1

Abstract

Fully grown germinal vesicle stage mouse oocytes remain arrested in meiotic prophase I until ovulation. This arrest is maintained by cGMP produced in cumulus granulosa cells surrounding the oocyte. Recently, it was found that cGMP production in cumulus cells depends on NPR2 guanylate cyclase activated by its ligand natriuretic peptide precursor C (NPPC). It is assumed that cGMP reaches the oocyte through gap junctions that couple cumulus granulosa cells to each other and to the oocyte. Previous work identified two main types of gap junctions in the follicle, connexin-43 gap junctions (GJA1 protein) between granulosa cells and connexin-37 gap junctions (GJA4) between cumulus cells and the oocyte. However, it had not been established that both types are required for meiotic arrest mediated by NPPC/NPR2 signaling. To investigate this, we used connexin mimetic peptides (CMPs) that specifically disrupt gap junction isoforms within cumulus-oocyte complexes (COCs) and isolated antral follicles in culture. We furthermore developed a punctured antral follicle preparation to permit CMP access to the antral cavity in an otherwise intact follicle. CMP directed against connexin-43 (Cx43 CMP) overcame NPPC-mediated meiotic arrest in both isolated COCs and antral follicles. Cx37 CMP, in contrast, had no effect when present in the medium, but released oocyte arrest in the presence of NPPC when microinjected into the perivitelline space near the oocyte surface in COCs. This is consistent with both connexin isoforms being required for meiotic arrest and with the reported localization of connexin-43 throughout the cumulus cells and connexin-37 at the oocyte surface.

Effects of androgen on immunohistochemical localization of androgen receptor and Connexin 43 in mouse ovary

“…the major connexin subunit expressed in granulosa cells was Cx43, and heterodimer of connexin 37/43 mediated some communication between cumulus granulosa cells and the oocyte in mouse (Conti et al, 2012). According to the previous study, follicles lacking Cx43 arrested in early preantral stages and produced incompetent oocytes, so Cx43 was required for oocyte meiotic maturation (Richard and Baltz, 2014). Herein, most important is the connection between Cx43 expression and oocyte meiotic maturation.…”

Control of Oocyte Growth and Development by Intercellular Communication Within the Follicular Niche

“…cAMP in the oocyte is metabolized by phosphodiesterase (PDE)-3A (Bornslaeger et al 1984;Beers 1978, 1980;Jensen et al 2002;Richard et al 2001;Shitsukawa et al 2001;Tsafriri et al 1996;Vivarelli et al 1983). Within the follicle, the granulosa cells transfer cyclic GMP, an inhibitor of PDE3A, to the oocyte, again via the gap junctions (Norris et al 2009;Richard and Baltz 2014;Zhang et al 2010). This helps to maintain a high steady-state level of cAMP within the oocyte.…”

Genomic expression profiles in cumulus cells derived from germinal vesicle and MII mouse oocytes

“…It is well known that high concentrations of cAMP and cGMP in the oocyte cytoplasm lead to meiotic arrest, and that decreases in cAMP and cGMP concentrations in oocytes lead to resumption of meiosis to MII (Sánchez and Smitz 2012). In COCs, CCs communicate with each other and with the oocyte via two isoforms of gap junction proteins, namely GJA1 (connexin 43) and GJA4 (connexin 37), both of which can control cAMP and cGMP exchanges between the CCs and oocyte (Richard and Baltz 2014). In the present study, both GJA1 and GJA4 were downregulated in CCs after IVM, as was the GJA1 protein.…”