Department of Biological Sciences, Graduate School of Science and Technology, Kumamoto University, 2-39-1 Kurokami, Kumamoto, 860-8555, Japan.
Dev Growth Differ. 2012 Aug;54(6):660-71. doi: 10.1111/j.1440-169X.2012.01367.x.
Xtr in the fertilized eggs of Xenopus has been demonstrated to be a member of a messenger ribonucleoprotein (mRNP) complex that plays a crucial role in karyokinesis during cleavage. Since the Xtr is also present both in oocytes and spermatocytes and its amount increases immediately after spematogenic cells enter into the meiotic phase, this protein was also predicted to act during meiotic progression. Taking advantage of Xenopus oocytes' large size to microinject anti-Xtr antibody into them for inhibition of Xtr function, we examined the role of Xtr in meiotic progression of oocytes. Microinjection of anti-Xtr antibody into immature oocytes followed by reinitiation of oocyte maturation did not affect germinal vesicle break down and the oscillation of Cdc2/cyclin B activity during meiotic progression but caused abnormal spindle formation and chromosomal alignment at meiotic metaphase I and II. Immunoprecipitation of Xtr showed the association of Xtr with FRGY2 and mRNAs such as RCC1 and XL-INCENP mRNAs, which are involved in the progression of karyokinesis. When anti-Xtr antibody was injected into oocytes, translation of XL-INCENP mRNA, which is known to be repressed in immature oocytes and induced after reinitiation of oocyte maturation, was inhibited even if the oocytes were treated with progesterone. A similar translational regulation was observed in oocytes injected with a reporter mRNA, which was composed of an enhanced green fluorescent protein open reading frame followed by the 3' untranslational region (3'UTR) of XL-INCENP mRNA. These results indicate that Xtr regulates the translation of XL-INCENP mRNA through its 3'UTR during meiotic progression of oocyte.
Xtr 在非洲爪蟾受精卵中的研究表明，它是信使核糖核蛋白（mRNP）复合物的一个成员，在卵裂期的核分裂过程中发挥着至关重要的作用。由于 Xtr 也存在于卵母细胞和精母细胞中，并且在生殖细胞进入减数分裂阶段后其数量立即增加，因此该蛋白也被预测在减数分裂过程中发挥作用。利用非洲爪蟾卵母细胞体积大的特点，将抗 Xtr 抗体微注射到卵母细胞中以抑制 Xtr 功能，我们研究了 Xtr 在卵母细胞减数分裂过程中的作用。将抗 Xtr 抗体微注射到未成熟的卵母细胞中，然后重新启动卵母细胞成熟，这不会影响生殖细胞核的破裂以及 Cdc2/周期蛋白 B 活性在减数分裂过程中的振荡，但会导致减数分裂中期 I 和 II 时纺锤体形成异常和染色体排列。Xtr 的免疫沉淀显示 Xtr 与 FRGY2 和 mRNAs（如 RCC1 和 XL-INCENP mRNAs）的关联，这些 mRNAs 参与核分裂的进展。当将抗 Xtr 抗体注入卵母细胞时，即使卵母细胞用孕激素处理，已知在未成熟卵母细胞中受到抑制并在重新启动卵母细胞成熟后被诱导的 XL-INCENP mRNA 的翻译也被抑制。在注射了由增强型绿色荧光蛋白开放阅读框和 XL-INCENP mRNA 的 3'非翻译区（3'UTR）组成的报告 mRNA 的卵母细胞中观察到类似的翻译调控。这些结果表明，Xtr 通过其在卵母细胞减数分裂过程中的 3'UTR 调节 XL-INCENP mRNA 的翻译。
