General principle involved in the mechanism of oocyte maturation

这个合作项目的目的是为了让两个由dr .。Yoshitaka Nagahama（冈崎，日本）和J.L.Maller（丹佛，美国）合作阐明了脊椎动物，特别是两栖动物（Maller，美国）和鱼类（Nagahama，日本）中卵母细胞成熟调节机制的一般原理。在两栖动物（爪蟾）和鱼类（鲑鱼、金鱼等）中，促性腺激素（可能是类lh促性腺激素）负责触发卵母细胞成熟。然而，在这两种情况下，促性腺激素都不直接作用于卵母细胞，而是作用于卵巢卵泡细胞产生诱导成熟的激素（两栖动物的黄体酮和鱼类的17 α， 20 β -二羟基-4-孕-3-one， 17 α, 20 β - dp）。两种促成熟激素的作用部位都在卵母细胞表面；在黄鳝、虹鳟和比目鱼卵母细胞的质膜上发现了黄体酮和17α、20β - dp诱导的卵母细胞成熟的特异性表面受体。两个研究小组将继续合作纯化和表征这些类固醇激素膜受体。微量注射孕酮和17 α， 20 β - dp未能诱导卵母细胞成熟，这表明它们不直接作用于生发囊泡，而似乎是通过卵母细胞细胞质中的第三介质起作用。细胞质性质的第三种介质被称为成熟促进因子（MPF）。从爪蟾和金鱼（鲤鱼）卵母细胞中纯化并鉴定了MPF， MPF由cdc2激酶和细胞周期蛋白b两种常见成分组成，尽管爪蟾和金鱼卵母细胞中MPF的成分相同，但MPF激活机制在两种物种之间存在差异。在金鱼中，17 α， 20 β - dp诱导未成熟卵母细胞合成周期蛋白B，进而通过苏氨酸（Thr161）磷酸化激活先前存在的35 kda cdc2激酶，产生34 kda活性cdc2激酶。这些MPF在鱼类卵母细胞中的激活机制明显不同于爪蟾，在爪蟾中，细胞周期蛋白B存在于未成熟卵母细胞中，并与cdc2激酶形成复合物（pre-MPF）。此外，在非洲爪蟾卵母细胞中，cdc2激酶激活需要苏氨酸（Thr14）和酪氨酸（Tyr15）的去磷酸化。然而，在金鱼卵母细胞成熟过程中，酪氨酸（Tyr15）去磷酸化并不是cdc2激酶激活的先决条件，这一点值得怀疑，因为这种激活不受钒酸钠的抑制。钒酸钠是一种蛋白磷酸酶抑制剂，通常用于抑制cdc25的活性，它会使cdc2激酶的酪氨酸（Tyr15）去磷酸化，从而抑制cdc2激酶的激活。少

The purpose of this cooperative project was that two research groups directed by Drs.Yoshitaka Nagahama (Okazaki, Japan) and J.L.Maller (Denver, USA) collaborate to clarify the general principle involved in the regulatory mechanism of oocyte maturation in vertebrates, in particular amphibians (Maller, USA) and fishes (Nagahama, Japan).In both amphibians (Xenopus) and fishes (salmonids, goldfish, etc.), gonadotropins (probably LH-like gonadotropin) are responsible for triggering oocyte maturation. However, in both cases, gonadotropins do not act directly on the oocyte, but act on the ovarian follicle cells to produce maturation-inducing hormones (progesterone in amphibians and 17alpha, 20beta-dihydroxy-4-pregnen-3-one, 17alpha, 20beta-DP, in fishes). The site of the action of both maturation-inducing hormones is the surface of the oocytes ; specific surface receptors responsible for the progesterone-and 17alpha, 20beta-DP-induced oocyte maturation were found on the plasma membrane of Xe … More nopus, rainbow trout and flounder oocytes. Two research groups will continuously collaborate to purify and characterize these steroid hormone membrane receptors.Microinjection of progesterone and 17alpha, 20beta-DP failed to induce oocyte maturation, suggesting that they do not act directly on the germinal vesicle but seems to act through a third mediator in the oocyte cytoplasm. This third mediator of cytoplasmic nature has been called maturation-promoting factor (MPF). MPF was purified and characterized from oocytes of Xenopus and goldfish (carp), consisting of two common components, cdc2 kinase and cyclin B. Although the components of MPF in Xenopus and goldfish oocytes, are the same, the mechanisms of MPF activation are different between these two species. In goldfish, 17alpha, 20beta-DP induces immature oocytes to synthesize cyclin B, which in turn activates preexisting 35-kDa cdc2 kinase through its threonine (Thr161) phosphorylation, producing the 34-kDa active cdc2 kinase. These mechanisms of MPF activation in fish oocytes apparently differ from those in Xenopus, in which cyclin B is present in immature oocytes and forms a complex with cdc2 kinase (pre-MPF). Furthermore, in Xenopus oocytes, dephosphorylation of threonine (Thr14) and tyrosine (Tyr15) is required for cdc2 kinase activation. However, it is doubtful that tyrosine (Tyr15) dephosphorylation of cdc2 kinase is not a prerequisite for its activation during goldfish oocyte maturation, since the activation is not inhibited by vanadade, a protein phosphatase inhibitor commonly used for inhibiting cdc25 activity that dephosphorylates tyrosine (Tyr15) of cdc2 kinase, thereby inhibits its activation. Less