Department of Medicine, University of California, Los Angeles, CA 90095.
Department of Medicine, University of California, Los Angeles, CA 90095;
Proc Natl Acad Sci U S A. 2018 Oct 2;115(40):10100-10105. doi: 10.1073/pnas.1812622115. Epub 2018 Sep 17.
The nuclear lamina, an intermediate filament meshwork lining the inner nuclear membrane, is formed by the nuclear lamins (lamins A, C, B1, and B2). Defects or deficiencies in individual nuclear lamin proteins have been reported to elicit nuclear blebs (protrusions or outpouchings of the nuclear envelope) and increase susceptibility for nuclear membrane ruptures. It is unclear, however, how a complete absence of nuclear lamins would affect nuclear envelope morphology and nuclear membrane integrity (i.e., whether nuclear membrane blebs or protrusions would occur and, if not, whether cells would be susceptible to nuclear membrane ruptures). To address these issues, we generated mouse embryonic fibroblasts (MEFs) lacking all nuclear lamins. The nuclear lamin-deficient MEFs had irregular nuclear shapes but no nuclear blebs or protrusions. Despite a virtual absence of nuclear blebs, MEFs lacking nuclear lamins had frequent, prolonged, and occasionally nonhealing nuclear membrane ruptures. By transmission electron microscopy, the inner nuclear membrane in nuclear lamin-deficient MEFs have a "wavy" appearance, and there were discrete discontinuities in the inner and outer nuclear membranes. Nuclear membrane ruptures were accompanied by a large increase in DNA damage, as judged by γ-H2AX foci. Mechanical stress increased both nuclear membrane ruptures and DNA damage, whereas minimizing transmission of cytoskeletal forces to the nucleus had the opposite effects.
核层，一种位于核膜内层的中间丝网格，由核纤层蛋白（lamins A、C、B1 和 B2）组成。已经报道，单个核纤层蛋白的缺陷或缺乏会引起核泡（核膜的突起或外凸），并增加核膜破裂的易感性。然而，不清楚核纤层完全缺失会如何影响核膜形态和核膜完整性（即是否会发生核膜泡或突起，如果不会，细胞是否容易发生核膜破裂）。为了解决这些问题，我们生成了缺乏所有核纤层蛋白的小鼠胚胎成纤维细胞（MEFs）。核纤层蛋白缺失的 MEFs 具有不规则的核形状，但没有核泡或突起。尽管几乎没有核泡，但缺乏核纤层蛋白的 MEFs 经常发生、持续时间长且偶尔无法愈合的核膜破裂。通过透射电子显微镜观察，核纤层蛋白缺失的 MEFs 中的内核膜呈“波浪状”，内、外核膜有明显的不连续。核膜破裂伴随着大量的 DNA 损伤，这可以通过 γ-H2AX 焦点来判断。机械应激增加了核膜破裂和 DNA 损伤，而将细胞骨架力传递到细胞核的最小化则产生了相反的效果。
