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

排卵是由排卵前垂体释放的促黄体生成素（LH）激增触发的，是一个动态过程，导致成熟的可受精卵从卵泡中释放出来。这种被称为卵泡破裂的事件在过去的世纪一直是深入研究的主题。先前的研究主要在哺乳动物物种（包括人类）中进行，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碎来完成的，从而涉及蛋白水解酶。事实上，已经提出了多种蛋白酶作为使卵泡破裂的候选物。然而，尽管做了很多努力，但排卵期卵泡破裂所必需的蛋白酶尚未被鉴定。在这项研究中，我们研究了脊椎动物的排卵过程中的青鳉，特别是确定负责卵泡壁的蛋白水解降解的酶的目的。我们发现，在青鳉卵巢卵泡破裂涉及至少三种基质金属蛋白酶（MMPs）的合作，连同金属蛋白酶组织抑制剂-2b（TIMP-2b）蛋白。我们确定了这些蛋白质在卵泡破裂过程中的独立作用。我们的研究结果表明，明胶酶A诱导的IV型胶原蛋白的水解构成的基底膜，膜型2（MT 2）MMP降解存在于卵泡膜细胞层中的I型胶原蛋白，和MT 1-MMP和TIMP-2b参与明胶酶A的生产和调节。体外排卵系统使得有可能确定蛋白酶，是在青鳉排卵的关键，和使用类似的实验系统应有助于确定哺乳动物的排卵酶。

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.