Mermillod P, Dalbiès-Tran R, Uzbekova S, Thélie A, Traverso J-M, Perreau C, Papillier P, Monget P
Physiologie de la Reproduction et des Comportements, UMR 6175 INRA, CNRS, Université de Tours, Haras Nationaux, Nouzilly, France.
Reprod Domest Anim. 2008 Jul;43 Suppl 2:393-400. doi: 10.1111/j.1439-0531.2008.01190.x.
Mammalian ovaries contain a large stock of oocytes enclosed in primordial follicles. Ovarian cyclic activity induces some of these follicles to initiate growth towards a possible ovulation. However, most of these follicles terminate their growth at any moment and degenerate through atresia. In growing follicles, only a subset of oocytes are capable to support meiosis, fertilization and early embryo development to the blastocyst stage, as shown through embryo in vitro production experiments. This proportion of competent oocytes is increasing along with follicular size. Growing lines of evidence suggest that oocyte competence relies on the storage of gene products (messenger RNA or protein) that will be determinant to support early stages of embryo development, before full activation of embryonic genome. Given these facts, the question is: are these gene products stored in oocytes during late folliculogenesis, allowing an increasing proportion of them to become competent? Alternatively, these transcripts may be stored during early folliculogenesis as the oocyte grows and displays high transcription activity. Several arguments support this latter hypothesis and are discussed in this review: (i) many attempts at prolonged culture of oocytes from antral follicles have failed to increase developmental competence, suggesting that developmental competence may be acquired before antral formation; (ii) the recent discovery of oocyte secreted factors and of their ability to regulate many parameters of surrounding somatic cells, possibly influencing the fate of follicles between ovulation or atresia, suggests a central role of oocyte quality in the success of folliculogenesis. Finally, in addition to their role in interfollicular regulation of ovulation rate, late folliculogenesis regulation and atresia could also be seen as a selective process aimed at the elimination through follicular atresia of oocytes that did not succeed to store proper gene products set during their growth.
哺乳动物的卵巢中含有大量包裹在原始卵泡中的卵母细胞。卵巢的周期性活动会促使其中一些卵泡开始生长，有可能排卵。然而，这些卵泡中的大多数会随时停止生长，并通过闭锁而退化。在生长中的卵泡中，只有一部分卵母细胞能够支持减数分裂、受精以及早期胚胎发育至囊胚阶段，体外胚胎生产实验已证明了这一点。随着卵泡大小的增加，具备这种能力的卵母细胞比例也在上升。越来越多的证据表明，卵母细胞的能力依赖于基因产物（信使核糖核酸或蛋白质）的储存，这些产物对于在胚胎基因组完全激活之前支持胚胎发育的早期阶段具有决定性作用。鉴于这些事实，问题在于：这些基因产物是在卵泡发生后期储存在卵母细胞中的，从而使越来越多的卵母细胞具备能力吗？或者，这些转录本可能在卵泡发生早期随着卵母细胞的生长以及显示出高转录活性时就被储存了。有几个论据支持后一种假设，本文将对此进行讨论：（i）许多延长培养窦状卵泡卵母细胞的尝试都未能提高其发育能力，这表明发育能力可能在窦状卵泡形成之前就已获得；（ii）最近发现卵母细胞分泌因子及其调节周围体细胞许多参数的能力，这可能影响卵泡在排卵或闭锁之间的命运，这表明卵母细胞质量在卵泡发生成功过程中起着核心作用。最后，除了它们在卵泡间调节排卵率方面的作用外，卵泡发生后期的调节和闭锁也可被视为一个选择性过程，旨在通过卵泡闭锁消除那些在生长过程中未能成功储存适当基因产物的卵母细胞。
