Follicular development: the role of the follicular microenvironment in selection of the dominant follicle
Follicular development: the role of the follicular microenvironment in selection of the dominant follicle
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DOI：
10.1016/j.anireprosci.2004.04.031
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发表时间：
2004-07-01
影响因子：
2.2
通讯作者：
Yang, MY
中科院分区：
文献类型：
--
作者：
Fortune, JE;Rivera, GM;Yang, MY
内分泌信号在卵泡发育调控中的重要性早已被认识。然而，卵泡微环境在决定卵泡命运中也起着关键作用。本文综述了卵泡内IGF系统在牛优势卵泡选择中的作用。在牛的发情周期中，最大的窦卵泡在卵泡募集和DF选择的两个或三个连续波中发育。卵泡液中高浓度的雌二醇是优势卵泡和排卵前卵泡的标志，并且与低浓度的低分子量（MW）胰岛素样生长因子结合蛋白相关。（IGFBP-2、-4和-5），其可以阻止IGF与其受体结合。我们的研究表明，优势卵泡和排卵前卵泡也具有更高水平的IGFBP-4/-5蛋白酶活性，其是人IGFBP-4蛋白酶的牛等价物，妊娠相关血浆蛋白-A（PAPP-A）。对DF出现后分离的卵泡的研究表明，PAPP-A在DF的卵泡液中存在，只要它可以被检测为形态上占优势。为了检查队列中一个卵泡（未来DF）中较高水平的PAPP-A是否先于形态优势，从队列中一个卵泡明显大于其他卵泡之前获得的成对牛卵巢中分离出四个最大的卵泡，大约在一个卵泡首次被检测为形态优势时和优势建立良好后。对卵泡液中雌二醇、低MW IGFBP、游离IGF和PAPP-A变化的时间序列的分析表明，PAPP-A的增加是在未来DF中检测到的最早的生化差异，卵泡选择是从获得PAPP-A开始的一系列渐进变化的结果，这导致IGFBP-4和-5的减少以及游离IGF的增加，其与FSH协同作用以增加雌二醇的产生。通过注射小剂量重组牛（rb）FSH诱导的共显性卵泡都具有与对照小母牛的单一DF相似的PAPP-A水平，支持FSH在DE中诱导PAPP-A的假设作用。总之，这些结果表明FSH诱导的PAPP-A以及因此游离IGF在DE的选择中具有关键作用。其它实验提供了IGF对体外牛卵泡生长的起始和原始和初级卵泡存活的有害作用的证据。这些结果强调了卵泡微环境在决定卵泡命运中的重要性，并表明其影响可能具有阶段特异性。(C)2004 Elsevier B. V.保留所有权利。
The importance of endocrine signals in the regulation of follicular development has long been recognized. However, the follicular microenvironment also plays a critical role in determining follicular fate. This review summarizes our studies on the role of the intrafollicular IGF system in selection of the dominant follicle (DF) in cattle. During the bovine estrous cycle, the largest antral follicles develop in two or three successive waves of follicular recruitment and selection of a DF High concentrations of estradiol in the follicular fluid are the hallmark of dominant and preovulatory follicles and are associated with lower concentrations of low molecular weight (MW) insulin-like growth factor binding proteins (IGFBP-2, -4, and -5), which can prevent binding of IGF to its receptor. Our studies have shown that dominant and preovulatory follicles also have much higher levels of an IGFBP-4/-5 protease activity, which is the bovine equivalent of the human IGFBP-4 protease, pregnancy-associated plasma protein-A (PAPP-A). Studies of follicles isolated just after the emergence of the DF showed that PAPP-A is present in the follicular fluid of the DF as soon as it can be detected as morphologically dominant. To examine whether higher levels of PAPP-A in one follicle of the cohort (the future DF) precedes morphological dominance, the four largest follicles were isolated from pairs of bovine ovaries obtained before one follicle of the cohort was significantly larger the others, around the time that one follicle was first detected as morphologically dominant and after dominance was well established. Analysis of the temporal sequence of changes in estradiol, low MW IGFBPs, free IGF, and PAPP-A in the follicular fluid suggested that an increase in PAPP-A is the earliest biochemical difference yet detected in the future DF and that follicular selection is the result of a progressive series of changes beginning with the acquisition of PAPP-A, which leads to a decrease in IGFBP-4 and -5 and an increase in free IGF, which synergizes with FSH to increase estradiol production. Co-dominant follicles, induced by injection of small doses of recombinant bovine (rb) FSH, both had levels of PAPP-A similar to the single DF of control heifers, supporting the hypothesized role of FSH in the induction of PAPP-A in the DE Taken together, these results suggest a critical role for FSH-induced PAPP-A, and thus for free IGF, in the selection of the DE In contrast, other experiments provided evidence for a deleterious effect of IGF on the initiation of bovine follicular growth and the survival of primordial and primary follicles in vitro. These results underscore the importance of the follicular microenvironment in determining follicular fate and indicate that its effects can be stage-specific. (C) 2004 Elsevier B.V. All rights reserved.