Webb R, Nicholas B, Gong J G, Campbell B K, Gutierrez C G, Garverick H A, Armstrong D G
Division of Agricultural Sciences, School of Biosciences, University of Nottingham, Loughborough LE12 5RD, UK.
Reprod Suppl. 2003;61:71-90.
Reproductive function is an integrated process encompassing both extra-ovarian signals, such as gonadotrophins, and intrafollicular factors, such as locally produced growth factors. Initiation of primordial follicle growth and the early stages of folliculogenesis can occur without gonadotrophins. However, in vivo and in vitro studies indicate that FSH may stimulate the rate of preantral follicle growth and that it can take only 3 months for a primordial follicle to reach the ovulatory stage. Antral follicle development from 2 and 4 mm in diameter in sheep and cattle, respectively, is gonadotrophin dependent. During the oestrous cycle a transient increase in circulating FSH precedes the recruitment of a group of follicles. Recruited follicles are characterized by induction of expression of mRNAs encoding a range of steroidogenic enzymes, gonadotrophin receptors and local regulatory factors. As follicles continue to mature, there is a transfer of dependency from FSH to LH, which may be part of the mechanism involved in selection of follicles for continued growth. The mechanism of selection of the ovulatory follicle seems to be linked to the timing of mRNA expression encoding LHr and 3beta-hydroxysteroid dehydrogenase (3beta-HSD) in granulosa cells. Locally produced growth factors, such as the insulin-like growth factors (IGFs) and members of the transforming growth factor beta (TGFbeta) superfamily (inhibins, activins and bone morphogenetic proteins (BMPs)), work in concert with gonadotrophins throughout the follicular growth continuum. The roles of growth factors in follicular development and survival are dependent on gonadotrophin status and differentiation state, including morphology. In conclusion, it is the integration of extraovarian signals and intrafollicular factors that determine whether a follicle will continue to develop or be diverted into atretic pathways, as is the case for most of the follicles in monovulatory species, such as cattle.
生殖功能是一个综合过程，涵盖了卵巢外信号（如促性腺激素）和卵泡内因子（如局部产生的生长因子）。原始卵泡生长的启动和卵泡发生的早期阶段可以在没有促性腺激素的情况下发生。然而，体内和体外研究表明，促卵泡素（FSH）可能刺激窦前卵泡的生长速度，并且原始卵泡只需3个月就能达到排卵阶段。绵羊和牛的直径分别从2毫米和4毫米开始的窦卵泡发育依赖于促性腺激素。在发情周期中，循环中的FSH短暂升高先于一组卵泡的募集。募集的卵泡的特征是诱导编码一系列类固醇生成酶、促性腺激素受体和局部调节因子的mRNA表达。随着卵泡继续成熟，依赖性从FSH转移到促黄体素（LH），这可能是参与选择继续生长的卵泡的机制的一部分。排卵卵泡的选择机制似乎与颗粒细胞中编码LH受体（LHr）和3β-羟基类固醇脱氢酶（3β-HSD）的mRNA表达时间有关。局部产生的生长因子，如胰岛素样生长因子（IGFs）和转化生长因子β（TGFβ）超家族成员（抑制素、激活素和骨形态发生蛋白（BMPs）），在整个卵泡生长连续过程中与促性腺激素协同作用。生长因子在卵泡发育和存活中的作用取决于促性腺激素状态和分化状态，包括形态学。总之，决定卵泡是否会继续发育或转向闭锁途径的是卵巢外信号和卵泡内因子的整合，就像单胎动物（如牛）中的大多数卵泡那样。
