General principle involved in the mechanism of oocyte maturation

该合作项目的目的是由Yoshitaka Nagahama博士（日本冈崎）和J.L.Maller博士（美国丹佛）领导的两个研究小组合作阐明脊椎动物卵母细胞成熟调节机制的一般原理，特别是两栖动物（Maller，美国）和鱼类（Nagahama，日本）。在两栖动物（非洲爪蟾）和鱼类（鲑鱼，金鱼等）中，促性腺激素（可能是LH样促性腺激素）负责触发卵母细胞成熟。然而，在这两种情况下，促性腺激素并不直接作用于卵母细胞，而是作用于卵泡细胞以产生成熟诱导激素（两栖动物中的孕酮和鱼类中的17 α，20 β-二羟基-4-异戊烯-3-酮，17 α，20 β-DP）。这两种成熟诱导激素的作用部位都在卵母细胞的表面;在卵母细胞的质膜上发现了负责孕酮和17 α，20 β-DP诱导卵母细胞成熟的特异性表面受体。 ...更多信息 胭脂鱼、虹鳟鱼和比目鱼卵母细胞。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。显微注射孕酮和17 α，20 β-DP未能诱导卵母细胞成熟，表明它们不直接作用于生殖囊泡，但似乎通过卵母细胞胞质中的第三种介质起作用。这第三个介质的细胞质性质已被称为成熟促进因子（MPF）。MPF是从非洲爪蟾和金鱼卵母细胞中分离纯化的，由两个共同的组分cdc 2激酶和细胞周期蛋白B组成。虽然非洲爪蟾和金鱼卵母细胞中MPF的成分是相同的，但MPF的激活机制在这两个物种之间是不同的。在金鱼中，17 α，20 β-DP诱导未成熟卵母细胞合成细胞周期蛋白B，细胞周期蛋白B又通过其苏氨酸（Thr 161）磷酸化激活预先存在的35-kDa cdc 2激酶，产生34-kDa活性cdc 2激酶。这些MPF激活的机制在鱼卵母细胞中明显不同于非洲爪蟾，其中细胞周期蛋白B存在于未成熟的卵母细胞中，并与cdc 2激酶（前MPF）形成复合物。此外，在非洲爪蟾卵母细胞中，cdc 2激酶激活需要苏氨酸（Thr 14）和酪氨酸（Tyr 15）的去磷酸化。然而，值得怀疑的是，cdc 2激酶的酪氨酸（Tyr 15）去磷酸化不是金鱼卵母细胞成熟过程中其激活的先决条件，因为激活不被钒酸盐抑制，钒酸盐是一种蛋白磷酸酶抑制剂，通常用于抑制cdc 25活性，使cdc 2激酶的酪氨酸（Tyr 15）去磷酸化，从而抑制其激活。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