Fetal Development—Germ Cell Sex Differentiation

Abstract

The most common likely regulator of meiotic entry during either mammalian oogenesis or spermatogenesis is retinoic acid (RA) signaling. The main difference between mammalian male and female germ cell differentiation is the timing at which meiosis begins. In females, meiosis initiates prior to birth, however, this process occurs after birth in males. One current hypothesis states that during embryonic development, RA is produced within both urogenital ridges but while germ cells within a developing ovary receive this signal, germ cells in the testis are protected from RA and instead are exposed to this essential differentiation factor postnatally. There is now a large amount of data published to support this hypothesis and this article will summarize what is known about RA signaling in the fetal ovary and RA degradation to prevent meiotic entry in the fetal testis.