Meiosis-inducing and meiosis-preventing effects of sex steroid hormones on hamster fetal ovaries in organ culture.

Day 11 to day 15 p.c. female gonads were cultured for 6-8 days in chemically-defined media. In day 11 and day 12 p.c. ovaries grown in a non-hormonal medium, the germ cells were unable to enter meiosis; they were retained at a stage of oogonia or more frequently at a preleptotene stage. Ovaries of the same ages cultured in an estradiol-containing medium showed germ cells progressing through meiotic prophase in a way close to that in ovaries of equivalent age in vivo. That was the case of the germ cells in day 13 to day 15 p.c. ovaries maintained in a non-hormonal medium. In a testosterone-containing medium, the germ cells in day 13 and day 14 p.c. ovaries were prevented from entering meiosis; by contrast, those in day 15 p.c. ovaries underwent meiotic prophase normally. These results indicated that each of both hormones was able to exert its corresponding (meiosis-inducing or meiosis-preventing) effect before a definite critical time of ovarian development. The possibility is suggested that the germ cell differentiation in the female and male gonads in vivo would also depend on estrogens or androgens precociously synthesized in the gonads or supplied from other organs via the fetal blood.