Department of Pathology, University of Maryland School of Medicine, 800 W. Baltimore Street, Baltimore, MD 21201, USA.
Exp Cell Res. 2010 Mar 10;316(5):848-58. doi: 10.1016/j.yexcr.2009.11.018. Epub 2009 Dec 30.
Cortactin is a cortex-enriched protein implicated in Arp2/3 complex-mediated actin polymerization. However, the physiological role of cortactin remains unknown. We have generated a mouse strain in which the allele of murine cortactin was disrupted by a gene trapping vector. The resulting heterozygous mice developed normally and were fertile, but embryonic fibroblasts derived from heterozygous animals displayed partial impairment in PDGF-induced membrane ruffling. No homozygous offspring or early embryos even at the two-cell stage were detected. Analysis of oocytes revealed a gradual decrease in the detection of homozygous zygotes after fertilization. In normal oocytes arrested at meiotic metaphase II (MII), cortactin immunoreactivity was detected in an apical layer that overlies the maternal chromosome and overlaps with a polarized cortex enriched with actin. The formation of the polarized cortactin layer was diminished upon treatment with latrunculin B, an actin polymerization inhibitor. After resumption of meiosis II, the majority of cortactin protein was accumulated into the second polar body. Microinjection of MII-arrested eggs with either cortactin antibody or RNA encoding a cortactin mutant deficient in Arp2/3 complex binding disrupted the integrity of the actin cap and inhibited emission of the second polar body triggered by parthenogenesis. Our data suggest that cortactin plays an important role in the mechanics of asymmetric division in oocytes.
桩蛋白是皮层丰富的蛋白，参与 Arp2/3 复合物介导的肌动蛋白聚合。然而，桩蛋白的生理作用仍然未知。我们已经生成了一种小鼠品系，其中的小鼠桩蛋白等位基因被基因捕获载体所破坏。所得的杂合子小鼠正常发育且具有生殖能力，但来源于杂合子动物的胚胎成纤维细胞显示出 PDGF 诱导的质膜皱襞形成的部分缺陷。未检测到纯合子后代甚至在两细胞阶段。对卵母细胞的分析表明，在受精后，检测到纯合子合子的数量逐渐减少。在被阻滞在减数分裂中期 II（MII）的正常卵母细胞中，桩蛋白免疫反应性在覆盖母染色体的顶端层中被检测到，并且与富含肌动蛋白的极化皮层重叠。在用肌动蛋白聚合抑制剂拉普丁素 B 处理后，极化桩蛋白层的形成减少。在恢复减数分裂 II 之后，大多数桩蛋白被积累到第二极体中。用桩蛋白抗体或编码 Arp2/3 复合物结合缺陷的桩蛋白突变体的 RNA 微注射 MII 阻滞的卵母细胞破坏了肌动蛋白帽的完整性，并抑制了孤雌生殖引发的第二极体的发射。我们的数据表明，桩蛋白在卵母细胞的不对称分裂的力学中起着重要作用。
