National Centre for Biological Sciences, Tata Institute of Fundamental Research, GKVK Campus, Bellary Road, Bangalore 560065, India.
J R Soc Interface. 2010 Jun 6;7 Suppl 3(Suppl 3):S321-30. doi: 10.1098/rsif.2010.0039.focus. Epub 2010 Mar 31.
Nuclear shape and size are emerging as mechanistic regulators of genome function. Yet, the coupling between chromatin assembly and various nuclear and cytoplasmic scaffolds is poorly understood. The present work explores the structural organization of a prestressed nucleus in a variety of cellular systems ranging from cells in culture to those in an organism. A combination of laser ablation and cellular perturbations was used to decipher the dynamic nature of the nucleo-cytoplasmic contacts. In primary mouse embryonic fibroblasts, ablation of heterochromatin nodes caused an anisotropic shrinkage of the nucleus. Depolymerization of actin and microtubules, and inhibition of myosin motors, resulted in the differential stresses that these cytoplasmic systems exert on the nucleus. The onset of nuclear prestress was then mapped in two contexts--first, in the differentiation of embryonic stem cells, where signatures of prestress appeared with differentiation; second, at an organism level, where nuclear or cytoplasmic laser ablations of cells in the early Drosophila embryo induced a collapse of the nucleus only after cellularization. We thus show that the interplay of physical connections bridging the nucleus with the cytoplasm governs the size and shape of a prestressed eukaryotic nucleus.
核的形状和大小正在成为基因组功能的机械调节因子。然而，染色质组装与各种核和细胞质支架之间的偶联作用还了解甚少。本工作探讨了从培养细胞到生物体中的各种细胞系统中预应力核的结构组织。激光消融和细胞扰动的组合用于破译核质接触的动态性质。在原代小鼠胚胎成纤维细胞中，异染色质节点的消融导致核的各向异性收缩。肌动蛋白和微管的解聚以及肌球蛋白马达的抑制导致这些细胞质系统对核施加的差异应力。然后在两种情况下绘制了核预应力的起始——首先，在胚胎干细胞的分化中，预应力的特征随着分化而出现；其次，在生物体水平上，在早期果蝇胚胎中对细胞核或细胞质的激光消融仅在细胞化后才导致细胞核的崩溃。因此，我们表明，连接核与细胞质的物理连接的相互作用控制着预应力真核核的大小和形状。
