Effects of gonadotropin, estrogen, and progesterone on c-mos gene expression in mouse oocytes in vivo and in vitro.

ABSTRACT

OBJECTIVE: To analyze the effects of gonadotropin and ovarian steroid hormones on the gene expression of c-mos in mouse oocytes. METHODS: The changes of c-mos messenger RNA (mRNA) levels in oocytes were examined after the administration of pregnant mare's serum gonadotropin (PMSG) in vivo, or after incubation with estrogen and/or progesterone in vitro. Five IU PMSG was injected intraperitoneally to female immature mice, and human chorionic gonadotropin was also injected intraperitoneally 48 hours after the PMSG injection, with or without mating with male mice. The oocytes were collected from follicles or oviducts at 24, 30, 36, 42, 48, 60, 72, and 84 hours after the injection. The RNAs were extracted from 5 oocytes at each time point, and a reverse-transcription polymerase chain reaction using specific primers to c-mos DNA was performed to measure the relative amount of c-mos mRNA. RESULTS: The c-mos mRNA in oocytes at 36 hours after the injection was 2.7 times higher than that at 24 hours. The c-mos mRNA level gradually decreased thereafter, and after ovulation the level was only 1/10 of the peak level. When the oocytes that were retrieved 24 hours after PMSG injection were incubated with 800 ng/ml estradiol 17-beta or 600 ng/ml progesterone for 120 minutes, the c-mos gene expression was significantly suppressed or stimulated, respectively, in comparison with the absence of these substances. CONCLUSION: Although the regulatory mechanism of c-mos gene expression in oocytes is still unclear because the result obtained from the in vitro study, that estrogen suppressed the c-mos gene expression directly, was inconsistent with the result of the in vivo study, that increases of both c-mos mRNA and estrogen occurred simultaneously with PMSG stimulation in the early phase of preovulatory oocytes, our present study revealed that gonadotropin and steroid hormones might affect c-mos gene expression in mouse oocytes indirectly and/or directly.