Department of Human Genetics, University of Pittsburgh, Pittsburgh, PA 15261.
Department of Medicine, University of Pittsburgh, Pittsburgh, PA 15213.
Proc Natl Acad Sci U S A. 2019 Mar 5;116(10):4307-4315. doi: 10.1073/pnas.1810070116. Epub 2019 Feb 14.
The nuclear lamina is an intermediate filament meshwork adjacent to the inner nuclear membrane (INM) that plays a critical role in maintaining nuclear shape and regulating gene expression through chromatin interactions. Studies have demonstrated that A- and B-type lamins, the filamentous proteins that make up the nuclear lamina, form independent but interacting networks. However, whether these lamin subtypes exhibit a distinct spatial organization or whether their organization has any functional consequences is unknown. Using stochastic optical reconstruction microscopy (STORM) our studies reveal that lamin B1 and lamin A/C form concentric but overlapping networks, with lamin B1 forming the outer concentric ring located adjacent to the INM. The more peripheral localization of lamin B1 is mediated by its carboxyl-terminal farnesyl group. Lamin B1 localization is also curvature- and strain-dependent, while the localization of lamin A/C is not. We also show that lamin B1's outer-facing localization stabilizes nuclear shape by restraining outward protrusions of the lamin A/C network. These two findings, that lamin B1 forms an outer concentric ring and that its localization is energy-dependent, are significant as they suggest a distinct model for the nuclear lamina-one that is able to predict its behavior and clarifies the distinct roles of individual nuclear lamin proteins and the consequences of their perturbation.
核层是一种紧邻内核膜(INM)的中间丝网格结构,它在维持核形状和通过染色质相互作用调节基因表达方面起着关键作用。研究表明,构成核层的 A 型和 B 型核纤层蛋白形成独立但相互作用的网络。然而,这些核纤层亚型是否表现出独特的空间组织,或者它们的组织是否具有任何功能后果尚不清楚。我们的研究使用随机光学重建显微镜(STORM)发现,核层蛋白 B1 和核层蛋白 A/C 形成同心但重叠的网络,核层蛋白 B1 形成位于内核膜附近的外同心环。核层蛋白 B1 的更外周定位是由其羧基末端法呢基基团介导的。核层蛋白 B1 的定位也依赖于曲率和应变,而核层蛋白 A/C 的定位则不依赖于曲率和应变。我们还表明,核层蛋白 B1 的面向外部的定位通过限制核层蛋白 A/C 网络的向外突起来稳定核形状。这两个发现,即核层蛋白 B1 形成一个外同心环,其定位是能量依赖的,这是非常重要的,因为它们提出了一个核层的独特模型,能够预测其行为,并阐明了单个核纤层蛋白的不同作用及其扰动的后果。