Involvement of PKCε in FSH-induced connexin43 phosphorylation and oocyte maturation in mouse.

Han Cai,Wei Liu,Chao Wang,Hong Ouyang,Yi Yang,Bingying Liu,Meijia Zhang,Jinrui Xu,Jing Wen,Zhangli Ni,Gang Ning,Zhiqing Wei,Guoliang Xia,Bo Zhou,Yuzhen Ma,Tingting Yang,Guangcun Deng,Junxia Li

doi:10.1242/bio.034678

Abstract

ABSTRACTGap junctions (GJs) are indispensable for communication between cumulus cells (CCs) and oocytes in coordinating the gonadotropin-induced meiotic maturation of oocytes. Of all proteins that constitute GJs, phosphorylated connexin43 (pCx43) is vital for mediating the actions of gonadotropins. In this study, the mechanism of Cx43 phosphorylation in response to follicle stimulating hormone (FSH) stimulation was examined using an in vitro model of mouse cumulus-oocyte complexes (COCs). The results confirmed that Cx43 phosphorylation occurred twice during FSH treatment. Importantly, the second Cx43 phosphorylation was closely related to cAMP level reduction within oocytes, which initiated oocyte maturation. Exploration of the underlying mechanism revealed that the CC-specific protein kinase C ε (PKCε) level was upregulated by FSH stimulation. PKCε was a kinase downstream from mitogen-activated protein kinase (MAPK) and was responsible for Cx43 phosphorylation. Interestingly, MAPK was involved in both Cx43 phosphorylation processes, while PKCε was only involved in the second. In conclusion, PKCε-mediated MAPK signals might contribute to Cx43 phosphorylation in CCs during FSH-induced oocyte meiotic resumption. Our findings contribute to a better understanding of the molecular regulation mechanism of oocyte maturation in response to FSH in vitro.

Highlights

In mammals, the endocrine control of meiotic arrest and resumption rests on a network of extracellular and intracellular molecular interactions within follicles (Zhang et al, 2011)
When mouse cumulusoocyte complexes (COCs) were cultured in hypoxanthine (HX) media for 24 h, over 80% of oocytes were sustained at the germinal vesicle (GV) stage, while approximately 78% of oocytes resumed meiosis in the follicle stimulating hormone (FSH) group (P
By the 12 h time point (TP), oocytes at the GV stage in the FSH group became significantly different from the control group; only 44.6% of oocytes were sustained at the GV stage in the FSH group, but approximately 86.3% of oocytes were sustained at the GV stage in the control group (P

Summary

Introduction

The endocrine control of meiotic arrest and resumption rests on a network of extracellular and intracellular molecular interactions within follicles (Zhang et al, 2011). The building blocks of GJs are connexins (Cxs), which are a family of approximately 20. GJs are essential for interactions between somatic cells and oocytes in follicles. With GJs, somatic cells can pass nutrients, e.g. amino acids and glucose, to support the growing metabolic requirements of an oocyte, ions to regulate the pH within the oocyte, or inhibitory signals, such as cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) from cumulus cells (CCs), to maintain meiotic arrest (Fagbohun and Downs, 1991; Downs, 1995; Conti et al, 2002; Thomas et al, 2004; Mehlmann, 2005; Kidder and Vanderhyden, 2010; Zhang et al, 2010). The functions of GJs during oocyte meiotic resumption are far from well understood

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