Regulation Of Follicle Development and Fertility By Activin and Follistatin

描述（由申请人提供）：目前的证据支持长期持有的概念，即雌性哺乳动物的生殖潜力是由出生时可用的未生长的原始卵泡存量决定的。当囊中有分裂活性的生殖细胞停止分裂并在减数分裂中停滞时，这些原始卵泡形成，之后囊破裂，一些卵母细胞被一些前颗粒细胞包围。这些原始卵泡中的一小部分每天离开休眠池，发育成生长的卵泡，最终产生可受精的雌性配子。了解这些过程的生化控制机制是重要的，因为缺陷可能导致人类许多不孕症综合征，包括卵巢早衰（POF），其中卵泡加速丢失被认为是一个可能的原因。调节囊肿破裂、原始卵泡形成和原始卵泡激活过程的因素在很大程度上是未知的，但最近的进展表明，激活素可能是决定卵泡池大小的关键成分。激活素是TGF2超家族的成员，受包括卵泡listatin （FST）在内的天然拮抗剂调节。FST基因产生3种具有不同生化特性和生物作用的蛋白亚型。为了确定这些作用，我们创建了一个小鼠模型，其中只产生最小的FST异构体FST288（仅FST288）。这些老鼠是低生育能力的，产仔数量和频率减少。有趣的是，fst288型的雌性在出生时具有更大的原始卵泡池，但与WT型雌性相比，这些卵泡的消耗速度更快，这表明激活素调节卵泡形成和生长启动。本提案的主要目标是确定激活素在调节卵泡形成、发育和丢失中的作用。我们的中心假设是激活素增加生殖细胞增殖，减少卵母细胞在形成原始卵泡时的凋亡，并增加原始卵泡离开静止池的数量。我们建议在Aim 1中确定激活素调节卵泡形成和损失的机制。fst288小鼠中额外卵泡的质量将在Aim 2中进行检查，而在Aim 3中，我们将检验原始卵泡丢失率增加导致fst288小鼠POF的假设。这些结果将为激活素、激活素类似物或FST拮抗剂在治疗POF患者方面的潜在应用提供重要的基础。该R21的长期目标是建立内源性激活素及其FST调控作为卵泡池大小和随年龄下降速率的关键决定因素，这可能与理解和治疗人类POF和其他不孕综合征的病理生理有关。拟议研究的结果也将支持未来的项目，使用有针对性和可调节的转基因技术来控制激活素表达的位点和时间，这将直接测试激活素的生殖作用。

DESCRIPTION (provided by applicant): Current evidence supports the long-held concept that the reproductive potential of female mammals is determined by the stock of non-growing, primordial follicles available at birth. These primordial follicles are formed when mitotically active germ cells in cysts cease dividing and arrest in meiosis, after which the cysts break down and some oocytes become surrounded by a few pre-granulosa cells. A small portion of these primordial follicles leave the resting pool each day and develop into growing follicles that eventually produce viable female gametes ready for fertilization. Understanding the biochemical control mechanism for these processes is important as defects could lead to a number of infertility syndromes in humans including premature ovarian failure (POF) in which accelerated loss of follicles is thought to be a possible cause. The factors regulating the processes of cyst breakdown, primordial follicle formation, and activation of primordial follicles are largely unknown but recent advances suggest that activin might be a critical component determining follicle pool size. Activin is a member of the TGF2 superfamily that is regulated by natural antagonists including follistatin (FST). The FST gene produces 3 protein isoforms which have different biochemical properties and biological actions. To determine these actions we created a mouse model in which only the smallest FST isoform, FST288 is made (FST288-only). These mice are subfertile with reduced litter size and frequency. Interestingly, FST288-only females are born with a larger pool of primordial follicles, but these follicles are depleted at a greater rate compared to WT females, suggesting that activin regulates both follicle formation and growth initiation. The broad goal of this proposal is to determine the role of activin in regulating follicle formation, development, and loss. Our central hypothesis is that activin increases germ cell proliferation, reduces apoptosis of oocytes as they form primordial follicles, and increases the number of primordial follicles leaving the resting pool. We propose to determine the mechanism(s) whereby activin regulates follicle formation and loss in Aim 1. The quality of the additional follicles in FST288-only mice will be examined in Aim 2, while in Aim 3 we will test the hypothesis that increased rate of primordial follicle loss leads to POF in FST288-only mice. These results will provide a critical foundation upon which potential applications of activin, activin analogs, or FST antagonists might be developed for treating POF patients. The long term goal of this R21 is to establish endogenous activin and its regulation by FST as critical determinants of follicle pool size and rate of decline with age, which could be relevant for understanding and treating the pathophysiology of POF and other infertility syndromes in humans. Results from the proposed research would also support future projects to use targeted and regulatable transgenic technology to control the site and timing of activin expression that will directly test activin's reproductive roles. PUBLIC HEALTH RELEVANCE: The number of eggs that female animals and humans are born with is their entire stock for their reproductive lifetime. When this stock is depleted, the ovary stops maturing new eggs, a process known as menopause in humans. In some fertility disorders, this process occurs earlier than expected, shortening the reproductive period for these patients and leaving them with few treatment options. The research in this proposal will investigate the role of activin and follistatin in regulating both the number of eggs, and the process of maturation, which could help define the defects that lead to early menopause, and to new treatments for this disorder.