The critical role of the MAP kinase pathway in meiosis II in Xenopus oocytes is mediated by p90Rsk
The critical role of the MAP kinase pathway in meiosis II in Xenopus oocytes is mediated by p90Rsk
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DOI：
10.1016/s0960-9822(00)00425-5
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发表时间：
2000-04-20
期刊：
影响因子：
9.2
通讯作者：
Maller, JL
中科院分区：
文献类型：
--
作者：
Gross, SD;Schwab, MS;Maller, JL
背景资料：在非洲爪蟾卵母细胞成熟过程中，孕酮诱导进入减数分裂I，减数分裂I和II的M期连续发生，没有S期的介入。有丝分裂原活化蛋白（MAP）激酶在减数分裂进入期间被激活，并且已经表明M期的连接反映了MAP激酶途径的激活和在后期I期间未能完全降解细胞周期蛋白B。为了分析MAP激酶通路在卵母细胞成熟中的功能，我们使用了U0126，一种有效的MAP激酶抑制剂，和一种组成型活性的MAP激酶靶蛋白激酶p90（Rsk）突变体。即使U0126完全抑制MAP激酶途径，在孕酮处理后，高达90%的卵母细胞能够进入减数分裂I，最有可能是通过polo样激酶Plx1激活磷酸酶Cdc25C。然而，随后，U0126处理的卵母细胞未能形成中期I纺锤体，未能重新积累细胞周期蛋白B到一个高水平，并未能过度磷酸化Cdc 27，后期促进复合物（APC）的一个组成部分，控制细胞周期蛋白B降解。这些卵母细胞进入S期而不是减数分裂II期。U0126处理的表达组成型活性形式p90（Rsk）的卵母细胞能够再积累细胞周期蛋白B，过度磷酸化Cdc 27，并在没有可检测到的MAP激酶活性的情况下形成中期纺锤体。MAP激酶通路对于非洲爪蟾进入减数分裂I不是必需的，但在减数分裂II开始期间需要抑制进入S期，调节APC以支持细胞周期蛋白B积累和支持纺锤体形成。此外，MAP激酶的一种底物p90（Rsk）足以在卵母细胞成熟期间介导这些作用。
Background: During oocyte maturation in Xenopus, progesterone induces entry into meiosis I, and the M phases of meiosis I and II occur consecutively without an intervening S phase. The mitogen-activated protein (MAP) kinase is activated during meiotic entry, and it has been suggested that the linkage of M phases reflects activation of the MAP kinase pathway and the failure to fully degrade cyclin B during anaphase I. To analyze the function of the MAP kinase pathway in oocyte maturation, we used U0126, a potent inhibitor of MAP kinase kinase, and a constitutively active mutant of the protein kinase p90(Rsk), a MAP kinase target.Results: Even with complete inhibition of the MAP kinase pathway by U0126, up to 90% of oocytes were able to enter meiosis I after progesterone treatment, most likely through activation of the phosphatase Cdc25C by the polo-like kinase Plx1. Subsequently, however, U0126-treated oocytes failed to form metaphase I spindles, failed to reaccumulate cyclin B to a high level and failed to hyperphosphorylate Cdc27, a component of the anaphase-promoting complex (APC) that controls cyclin B degradation. Such oocytes entered S phase rather than meiosis II. U0126-treated oocytes expressing a constitutively active form of p90(Rsk) were able to reaccumulate cyclin B, hyperphosphorylate Cdc27 and form metaphase spindles in the absence of detectable MAP kinase activity.Conclusions: The MAP kinase pathway is not essential for entry into meiosis I in Xenopus but is required during the onset of meiosis II to suppress entry into S phase, to regulate the APC so as to support cyclin B accumulation, and to support spindle formation. Moreover, one substrate of MAP kinase, p90(Rsk), is sufficient to mediate these effects during oocyte maturation.