Gounon P, Karsenti E
J Cell Biol. 1981 Feb;88(2):410-21. doi: 10.1083/jcb.88.2.410.
In the present work, we show that actin is present in considerable quantities in the oocyte nucleus of the newt Pleurodeles waltlii. The nuclear sap, extracted in saline buffer containing Ca++, is fluid. DNAase I inhibition assays have shown that 90% of actin is under a globular state in such conditions. Chelation of Ca++ by EGTA leads to the formation of a nuclear gel composed of individual microfilaments. This nuclear gel contains approximately 50% of total nuclear actin in a filamentous form. Phalloidin, a drug known to stabilize F-actin, induces the formation of a network of actin cables in the nuclei. This network contains nearly 100% of total nuclear actin in the filamentous form. The observation of the cables in the electron microscope shows that they are made of tightly associated microfilaments to which RNP-like particles are bound. The actin antibodies stain the cables and the particles by the indirect immunoperoxidase technique; myosin antibodies mainly stain the particles. The formation of the phalloïdin-induced network seems to require the presence of Ca++, Mg++, and ATP. We propose a scheme for the regulation of the supramolecular forms of actin in oocyte nuclei in which a delicate equilibrium seems to exist between globular actin, microfilaments, and actin cables. This equilibrium would be controlled by the concentration of Ca++, ATP, and various actin-associated proteins.
在本研究中，我们发现蝾螈（Pleurodeles waltlii）卵母细胞核中存在大量肌动蛋白。在含Ca++的盐缓冲液中提取的核液呈液态。DNA酶I抑制试验表明，在这种条件下，90%的肌动蛋白处于球状状态。EGTA对Ca++的螯合导致由单个微丝组成的核凝胶形成。这种核凝胶含有约50%的丝状形式的总核肌动蛋白。鬼笔环肽是一种已知能稳定F-肌动蛋白的药物，它能诱导细胞核中形成肌动蛋白束网络。该网络含有近100%的丝状形式的总核肌动蛋白。在电子显微镜下观察这些束，发现它们由紧密相连的微丝组成，RNP样颗粒附着在微丝上。肌动蛋白抗体通过间接免疫过氧化物酶技术对束和颗粒进行染色；肌球蛋白抗体主要对颗粒进行染色。鬼笔环肽诱导的网络的形成似乎需要Ca++、Mg++和ATP的存在。我们提出了一个卵母细胞核中肌动蛋白超分子形式调控的方案，其中球状肌动蛋白、微丝和肌动蛋白束之间似乎存在微妙的平衡。这种平衡将由Ca++、ATP和各种肌动蛋白相关蛋白的浓度控制。
