McLaren A
Wellcome/CRC Institute, Cambridge, U.K.
Philos Trans R Soc Lond B Biol Sci. 1995 Nov 29;350(1333):229-33. doi: 10.1098/rstb.1995.0156.
Whether germ cells succeed in making eggs or sperm depends both on their genetic constitution and on the tissue environment in which they develop. The decision as to whether it is oogenesis or spermatogenesis on which they initially embark depends only on their environment, however, and not at all on their own chromosomes. The foetal testis of the mouse produces an inhibitor of meiosis: germ cells that are exposed to it develop as prospermatogonia. Germ cells in the foetal ovary enter meiosis and develop as oocytes: this may represent the default pathway for germ cell sexual differentiation, or there may exist a meiosis-inducing substance. Experimental evidence suggests that any such substance must be present ubiquitously, not just in the ovary. The stage of foetal development at which meiosis is initiated may be programmed in the germ cell lineage.
生殖细胞能否成功发育成卵子或精子，既取决于它们的基因构成，也取决于它们发育所处的组织环境。然而，它们最初开始的是卵子发生还是精子发生，这一决定仅取决于它们所处的环境，而完全不取决于它们自身的染色体。小鼠的胎儿睾丸会产生一种减数分裂抑制剂：暴露于该抑制剂的生殖细胞会发育为原精原细胞。胎儿卵巢中的生殖细胞进入减数分裂并发育为卵母细胞：这可能代表了生殖细胞性别分化的默认途径，或者可能存在一种诱导减数分裂的物质。实验证据表明，任何此类物质必定普遍存在，而不仅仅存在于卵巢中。减数分裂开始的胎儿发育阶段可能在生殖细胞谱系中就已被编程。
