Mermillod P, Oussaid B, Cognié Y
Institut National de la Recherche Agronomique, Station de Physiologie de la Reproduction des Mammiferes Domestiques, Nouzilly, France.
J Reprod Fertil Suppl. 1999;54:449-60.
The ability to mature, be fertilized and finally to develop into a viable embryo is acquired gradually by the oocyte during progressive differentiation throughout folliculogenesis. This process starts with oocyte growth during the first steps of follicular development. As the oocyte is close to its final size, other modifications occur, less spectacular but at least as important in determining the resulting ability of the oocyte to accomplish its reproductive purpose (developmental competence). These modifications, referred to as 'oocyte capacitation', are probably influenced by the follicle. The proportion of developmentally competent oocytes increases with follicular size. However, the relationship between follicular growth and oocyte competence is not very strict, since a given oocyte may acquire its competence at any stage of follicular growth and since some examples of functional disjunction between follicular size and oocyte competence are described. Follicular atresia may impair the acquisition of oocyte competence, as evidenced by the parallel study of follicular characteristics and of the developmental potential of their oocytes treated individually through in vitro maturation, fertilization and development. However, when atresia is experimentally induced in large preovulatory follicles, oocytes remain competent, indicating that once competence is acquired, it is no longer sensitive to atresia. Oocyte maturation represents only the end of this long and progressive process and validates the preparation of the oocyte by conferring its final developmental ability. As evidenced by recent cloning experiments, the cytoplasmic aspects of oocyte maturation are crucial for the acquisition of developmental competence. This cytoplasmic maturation may be activated in vitro by the use of complex media supplement (serum, follicular fluid) but the use of defined media for maturation allowed the identification of some active factors (such as epidermal growth factor, growth hormone, inhibin and activin). The study of some differential models of oocyte competence (follicular size and atresia, Booroola gene, prepubertal oocytes) will provide a better understanding of oocyte capacitation and maturation, and allow the improvement of in vitro methods for oocyte maturation, which represent the most limiting step of in vitro production of embryos in large mammals.
在卵泡发生过程中，卵母细胞在逐渐分化的过程中逐渐获得成熟、受精并最终发育成有活力胚胎的能力。这个过程始于卵泡发育的最初阶段卵母细胞的生长。当卵母细胞接近其最终大小时，会发生其他变化，这些变化不太明显，但在决定卵母细胞实现其生殖目的（发育能力）的最终能力方面至少同样重要。这些变化被称为“卵母细胞获能”，可能受卵泡影响。发育能力正常的卵母细胞比例随卵泡大小增加。然而，卵泡生长与卵母细胞能力之间的关系并不十分严格，因为给定的卵母细胞可能在卵泡生长的任何阶段获得其能力，并且因为描述了卵泡大小与卵母细胞能力之间功能分离的一些例子。卵泡闭锁可能会损害卵母细胞能力的获得，通过对卵泡特征及其通过体外成熟、受精和发育单独处理的卵母细胞的发育潜力进行平行研究可以证明这一点。然而，当在大型排卵前卵泡中实验性诱导闭锁时，卵母细胞仍具有能力，这表明一旦获得能力，它就不再对闭锁敏感。卵母细胞成熟仅仅是这个漫长而渐进过程的终点，并通过赋予其最终发育能力来验证卵母细胞的准备情况。正如最近的克隆实验所证明的，卵母细胞成熟的细胞质方面对于获得发育能力至关重要。这种细胞质成熟可以通过使用复杂的培养基补充剂（血清、卵泡液）在体外激活，但使用确定的培养基进行成熟可以鉴定一些活性因子（如表皮生长因子、生长激素、抑制素和激活素）。对一些卵母细胞能力的差异模型（卵泡大小和闭锁、Booroola基因以及青春期前卵母细胞）进行研究将更好地理解卵母细胞获能和成熟，并有助于改进卵母细胞成熟的体外方法，而这是大型哺乳动物胚胎体外生产中最具限制性的步骤。
