Studies on the mechanism of ovulation in vertebrates by post-genomic approaches

排卵是由垂体释放的促黄体生成素（LH）在排卵前激增引发的，这是一个动态的过程，导致成熟的可受精卵从卵泡中解放出来。这种被称为卵泡破裂的事件在过去的一个世纪里一直是深入研究的主题。先前的研究主要是在哺乳动物物种中进行的，包括人类，已经确定卵泡破裂是通过颗粒细胞基底膜的溶解和卵泡壁顶端胶原基质的破裂来完成的，从而涉及蛋白质水解酶。事实上，有多种蛋白酶被认为是导致卵泡破裂的原因。然而，尽管付出了很多努力，但在排卵过程中卵泡破裂所必需的蛋白酶尚未被确定。在这项研究中，我们研究了脊椎动物在medaka的排卵过程，特别目的是确定负责卵泡壁蛋白水解降解的酶。我们发现，至少三种基质金属蛋白酶（MMPs）和组织金属蛋白酶2b （TIMP-2b）蛋白共同作用导致了medaka卵巢卵泡破裂。我们确定了这些蛋白在卵泡破裂过程中的离散作用。我们的研究结果表明，明胶酶A诱导构成基底膜的IV型胶原的水解，膜2型（MT2） MMP降解存在于卵膜细胞层的I型胶原，MT1-MMP和TIMP-2b参与明胶酶A的产生和调节。体外排卵系统使鉴定对medaka排卵至关重要的蛋白酶成为可能。使用类似的实验系统应该有助于识别哺乳动物的排卵酶。

Ovulation, which is triggered by a preovulatory surge of luteinizing hormone (LH) released from the pituitary gland, is a dynamic process that results in the liberation of a mature fertilizable ovum from the ovarian follicle. This event, which is known as follicle rupture, has been the subject of intensive investigation over the past century. Previous studies, which have been carried out mainly in mammalian species, including humans, have established that follicle rupture is accomplished by dissolution of the granulosa cell basement membrane and fragmentation of the collagenous matrix at the apex of the follicular wall, thereby implicating proteolytic enzymes. Indeed, a variety of proteases have been proposed as candidates for rupturing the follicle. However, the proteases that are essential for follicle rupture in ovulation have not yet been identified, despite much effort. In this study, we investigated vertebrate ovulatory processes in the medaka, with the particular aim of identifying the enzymes responsible for the proteolytic degradation of the follicle walls. We found that follicle rupture in the medaka ovary involves the cooperation of at least three matrix metalloproteinases (MMPs), together with the tissue inhibitor of metalloproteinase-2b (TIMP-2b) protein. We determined the discrete roles of each of these proteins during follicle rupture. Our results indicate that gelatinase A induces the hydrolysis of type IV collagen constituting the basement membrane, membrane-type 2 (MT2) MMP degrades type I collagen present in the theca cell layer, and MT1-MMP and TIMP-2b are involved in the production and regulation of gelatinase A. The in vitro ovulation system made it possible to identify proteases that are critical for ovulation in the medaka, and the use of similar experimental systems should help to identify ovulatory enzymes in mammals.