| The process of mammalian oocyte formation, development and maturation was a process of meiosis control. In fetal gonad, oogonia become to primary oocytes by beginning of the first meiosis, and oocytes will be enclosed by ovarian somatic cells and further form the primordial follicles. However, the oocytes will arrest the first meiosis at prophase in their follicles. After a long development and acquiring the meiotic resumption competence, oocytes in preovulatory follicles will resume meiosis to mature under the stimulation of preovulatory gonadotropins surge. Thus, it is highly important of the regulation of meiosis to the formation, development and maturation of oocytes. Meiosis-activating sterol (MAS) was found to induce the meiotic resumption of mouse oocytes, thus, the function of MAS attracted attention of many scientists. However, it is a problem at present. In this study, we investigated the effects of MAS on the meiosis of mouse oocytes.MAS were first purified and identified by Byskov and her colleagues, MAS from human follicle fluid was termed by FF-MAS and MAS from bull testis tissue fluid was termed by T-MAS. FF-MAS and T-MAS both were intermediates in the biosynthesis pathway of cholesterol in mammals. FF-MAS was synthesized by lanosterol 14a-demethylase (CYP51) and further converted to T-MAS by A14-reductase. Inhibitors of CYP51, such as azalanstat (RS-2I607) and RS-2I745, could inhibit the synthesis of FF-MAS to decrease the accumulation of FF-MAS. Inhibitor of A14-reductase, such as AY9944-A-7, could inhibit the metabolism of FF-MAS to increase the accumulation of FF-MAS; and some other reagents, such as Nystatin, could combine with the downstream intermediate in the cholesterol biosynthesis pathway to accumulate MAS. In this study, we investigated the role of MAS by using these reagents to change the level of endogenous FF-MAS.Using the mouse fetal ovary serum-free culture model, fetal ovaries from 14 day post coitus (14 dpc) mouse were cultured, and treated by AY9944-A-7, Nystatin and RS-21745. The results showed that 0.025, 0.0625 and 0.125 uM AY9944-A-7 or 25, 50 and 75 iu/ml Nystatin increased the total number of follicles per ovary significantly; however, AY9944-A-7 and Nystatin at the same doses couldn't cause the same effect on the number of growing follicles and the average diameter of five largest follicles per ovary. 50 u.M RS-21745 decreased the total number of follicles, the number of growing follicles and diameter of follicles per ovary significantly after 48 h. 25 U.M RS-21745 could decrease the total number of follicles as well, but couldn't make a significant difference. The results demonstrated that MAS could promote the formation of follicle in fetal mouse ovaries, but MAS couldn't promote the initiation of follicle growth It suggested that MAS promote oogonia to initiate meiosis and to become oocytes and then to format follicles.In the present study, two models for short-term culture of intact mouse follicles under serum-free conditions were established. Follicles were obtained from immature mice that either had not received ovarian stimulation (model I) (i.e. without previous eCG priming) or had undergone ovarian stimulation (model II) (i.e. primed with eCG 45 hours before use). In model I, follicles were cultured for 24 hours and treated by FSH (0.01, 0.05 and 0.2 iu/ml) and/or hCG (0.1 and 10 iu/ml) and AY9944-A-7 (5, 25and 50 uM). Follicles were evaluated according to their size, i.e. follicular diameter (100 -170 urn, 180 - 200 um, 210 - 250 um, 260 - 350 urn and 360 - 400 urn). In model II, follicles of 360 - 400 urn in diameter were cultured for 6 hours and treated by 0.05 iu/ml FSH, 10 iu/ml hCG, RS-21745 (1, 50 and 100 uM) and azalanstat (RS-21607, 50 uM). In model I, FSH and AY9944-A-7 each induced resumption of meiosis in oocytes derived from all follicle sizes except those smaller than 180 um. hCG exhibited a similar but weaker effect on oocyte maturation, but only in follicles with a diameter of 260 -400 um. In model II only FSH (0.05 iu/ml) but n...
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