A selective block of nuclear actin export stabilizes the giant nuclei of Xenopus oocytes
A selective block of nuclear actin export stabilizes the giant nuclei of Xenopus oocytes
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DOI：
10.1038/ncb1357
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发表时间：
2006-03-01
影响因子：
21.3
通讯作者：
Görlich, D
中科院分区：
文献类型：
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作者：
Bohnsack, MT;Stüven, T;Görlich, D
肌动蛋白是一种主要的细胞骨架元素，通常通过输出蛋白6（Exp 6）驱动的核输出保持在细胞质中。在这里，我们表明，Exp 6识别肌动蛋白的功能，是保守的从酵母到人类。然而，令人惊讶的是，显微注射的肌动蛋白没有输出从非洲爪蟾卵母细胞核，除非Exp 6共注射，表明该途径在这种细胞类型中是无活性的。事实上，Exp 6在卵母细胞中检测不到，但从减数分裂成熟开始合成，这解释了肌动蛋白输出如何在胚胎发生后期恢复。因此，Exp 6代表了严格发育调控的核转运途径的第一个例子。我们问为什么非洲爪蟾卵母细胞缺乏Exp 6，并观察到异位应用Exp 6使巨大的卵母细胞核非常脆弱。这种效应与海绵状核内骨架的F-肌动蛋白的选择性消失有关。这些细胞核具有正常的G2期DNA含量，其体积比体细胞的细胞核大100，000倍。显然，它们的机械完整性不能通过染色质和相关的核基质来维持，而是需要核内肌动蛋白支架。
Actin is a major cytoskeletal element and is normally kept cytoplasmic by exportin 6 (Exp6)-driven nuclear export. Here, we show that Exp6 recognizes actin features that are conserved from yeast to human. Surprisingly however, microinjected actin was not exported from Xenopus laevis oocyte nuclei, unless Exp6 was co-injected, indicating that the pathway is inactive in this cell type. Indeed, Exp6 is undetectable in oocytes, but is synthesized from meiotic maturation onwards, which explains how actin export resumes later in embryogenesis. Exp6 thus represents the first example of a strictly developmentally regulated nuclear transport pathway. We asked why Xenopus oocytes lack Exp6 and observed that ectopic application of Exp6 renders the giant oocyte nuclei extremely fragile. This effect correlates with the selective disappearance of a sponge-like intranuclear scaffold of F-actin. These nuclei have a normal G2-phase DNA content in a volume 100,000 times larger than nuclei of somatic cells. Apparently, their mechanical integrity cannot be maintained by chromatin and the associated nuclear matrix, but instead requires an intranuclear actin-scaffold.