Reducing CYP51 inhibits follicle-stimulating hormone induced resumption of mouse oocyte meiosis in vitro

Abstract

This article is available online at http://www.jlr.orgMammalian oocytes arrested at the diplotene stage of the fi rst meiotic division are triggered to initiate meiosis by the preovulatory gonadotrophin surge in vivo, especially LH surge ( 1, 2 ). It has recently been suggested that certain intermediates of cholesterol biosynthesis, such as meiosis activating sterol (MAS), one of the upstream materials for synthesize of steroid hormones, instruct the oocyte to reinitiate meiosis ( 3-6 ). In invertebrate animals, such as xenopus, gonadotrophins induce progesterone secretion and initiate oocyte meiotic resumption. However, in mammals, whether gonadotrophins employ sterol to induce oocyte meiosis is still a pending question. In fact, sterol has the capacity to induce oocyte meiotic resumption. For example, Byskov et al. ( 7-10 ) fi rst discovered that fetal ovaries, which were cocultured with fetal testis, promoted sperm meiosis by secreting a meiosis activating substance. Later, Xia et al. ( 11 ) reported the substance may be a sterol because it is stable for heat. Byskov et al. ( 12 ) purifi ed and identifi ed the sterols from women's follicle fl uid and cattle's testis and nominated them as follicular fl uid derived-meiosis activating sterol and testis-meiosis activating sterol. Follicular fl uid derived-meiosis activating sterol, a direct product of lanosterol 14 ␣ -demethylase (CYP51) ( 13 ), had a dose-dependent effect on stimulating germinal vesicle breakdown (GVBD) in rodent, bovine, and human meiotically arrested oocytes ( 3,4,(14)(15)(16)(17)(18)(19)(20).To better understand the mechanism by which gonadotrophin employs CYP51-mediated sterol as the downstream signal to induce oocytes meiosis, many chemicals, such as Abstract Meiosis activating sterol, produced directly by lanosterol 14-␣ -demethylase (CYP51) during cholesterol biosynthesis, has been shown to promote the initiation of oocyte meiosis. However, the physiological signifi cance of CYP51 action on oocyte meiosis in response to gonadotrophins' induction remained to be further explored. Herein, we analyzed the role of CYP51 in gonadotrophin-induced in vitro oocyte maturation via RNA interference (RNAi). We showed that although both luteinizing hormone (LH) and follicle-stimulating hormone (FSH) signifi cantly induced meiotic resumption in follicle-enclosed oocytes (FEOs), the effect of LH on oocyte meiosis resumption in FEOs was weaker than FSH. Moreover, both FSH and LH were able to upregulate CYP51 expression in cultured follicular granulosa cells when examined at 8 h or 12 h posttreatments, respectively. Interestingly, whereas knockdown of CYP51 expression via small interference RNA (siRNA) moderately blocked (23% reduction at 24 h) FSH-induced oocyte maturation [43% germinal vesicle breakdown (GVBD) rate in RNAi vs. 66% in control, P < 0.05] in FEOs, similar treatments showed no apparent effects on LH-induced FEO meiotic maturation (58% GVBD rate in RNAi vs. 63% in control, P > 0.05). Moreover, the results in a cumulus-enclosed oocytes (CEOs)...

Retinoic acid signaling in regulation of meiosis during embryonic development in mice

“…Recent research has further elucidated a connection between RA regulation of Rec8 and CYP51 (Mu et al, 2018). FF-MAS itself was considered to be meiosis-inducing substance secreted by fetal ovaries, which could induce meiosis in fetal male germ cells (Byskov & Saxen, 1976), and had capacity to reinitiate meiotic resumption in mice oocytes in vitro (Wang et al, 2009 FF-MAS itself was considered to be meiosis-inducing substance secreted by fetal ovaries, which could induce meiosis in fetal male germ cells (Byskov & Saxen, 1976), and had capacity to reinitiate meiotic resumption in mice oocytes in vitro (Wang et al, 2009 …”

“…CYP51 catalyzes the conversion of lanosterol to follicular fluid meiosis-activating sterol (FF-MAS) (Stromstedt et al, 1998). FF-MAS itself was considered to be meiosis-inducing substance secreted by fetal ovaries, which could induce meiosis in fetal male germ cells (Byskov & Saxen, 1976), and had capacity to reinitiate meiotic resumption in mice oocytes in vitro (Wang et al, 2009)…”

Estrogen receptors in granulosa cells govern meiotic resumption of pre-ovulatory oocytes in mammals

“… 24 , 25 , 26 Thus, understanding the mechanisms of FSH and LH controlling follicular development and oocyte maturation is critical for improving the effectiveness of assisted reproduction techniques (ARTs) in clinical applications. In addition, series of studies have indicated that FSH alone is sufficient to induce oocyte maturation in vitro , 27 , 28 , 29 , 30 which is contradictory with that in vivo . However, the related mechanisms are poorly understood.…”

RNA interference and ovarian functions

“…The knockdown of CYP51 expression via siRNAs inhibited FSH-, but not LH-induced meiosis in mouse oocytes (Wang et al, 2009a). Furthermore, cultured mouse oocyte-granulosa cell complexes injected with siRNAs of mouse zona pellucida glykoprotein A (ZpA) had reduced growth and survival and abnormal morphology of zona pellucida.…”