Abstract
Meiosis activating sterol, produced directly by lanosterol 14-alpha-demethylase (CYP51) during cholesterol biosynthesis, has been shown to promote the initiation of oocyte meiosis. However, the physiological significance 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) significantly 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) model showed that approximately 30% of FSH-induced CEOs' meiotic resumption was blocked upon CYP51 knockdown by siRNAs. These findings suggest that FSH, partially at least, employs CYP51, and therefore the MAS pathway, to initiate oocyte meiosis.
Highlights
Meiosis activating sterol, produced directly by lanosterol 14-␣-demethylase (CYP51) during cholesterol biosynthesis, has been shown to promote the initiation of oocyte meiosis
RNA interference (RNAi) knocked down Enhance green florescence protein plasmid (EGFP) and CYP51 expression in cultured follicular granulosa cells In Fig.1A–C, the expression of positively transfected EGFP was significantly reduced by EGFP-small interference RNA (siRNA)
In vitro cultured mouse follicular granulosa cells, cumulus cells-enclosed oocyte (CEO), and follicle-enclosed oocyte (FEO) models were established to study the relationship between CYP51 expression and gonadotrophin-induced oocytes meiosis
Summary
Meiosis activating sterol, produced directly by lanosterol 14-␣-demethylase (CYP51) during cholesterol biosynthesis, has been shown to promote the initiation of oocyte meiosis. 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 [3,4,5,6] In invertebrate animals, such as xenopus, gonadotrophins induce progesterone secretion and initiate oocyte meiotic resumption. Follicular fluid 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].
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