Meiosis in fetal freemartin gonads and in rat fetal ovaries in vitro

Abstract

In the gonads of male or female calf fetuses and of fetal freemartins, the germ cells may present nuclear aspects resembling those described in other species as the « preleptotene chromosome condensation stage ». The maximum of these aspects occurred between 60 and 80 days post-insemination. The fate of the cells presenting these aspects is not know, and it is not certain that this nuclear stage really is part of meiosis. If one takes as a criterion the more conventionally recognized figures (leptotene, zygotene), meiosis was seen in the three freemartin fetuses aged 77 to 88 days, but the percentage of meiotic cells was low. In fetuses older than 90 days no meiotic cells were present in those gonads in which seminiferous cords developed. In gonads which contained no seminiferous cords, meiotic figures were seen only in three animals under 133 days of age ; in older animals meiosis was not present. The presence of seminiferous cords in the gonad is incompatible with the presence of meiotic germ cells. In every case, the germ cells disappeared from the freemartin gonad after day 186, except for a few which persisted until day 222 because they were located in seminiferous cords. In an attempt to determine whether meiosis could be influenced by various agents, rat fetal ovaries were cultivated in vitro with or without estradiol, an anti-estrogen, progesterone, methyladenine, ram rete fluid or « inhibine » extracted from ram rete fluid. In these preliminary non-quantitative experiments, no definite alterations of meiosis were noted.