Department of Experimental Medical Science, Lund University, Lund 22184, Sweden;
Asylum Research, an Oxford Instruments Company, Santa Barbara, CA 93117.
Proc Natl Acad Sci U S A. 2022 Mar 1;119(9). doi: 10.1073/pnas.2114121119.
Maintaining nuclear integrity is essential to cell survival when exposed to mechanical stress. Herpesviruses, like most DNA and some RNA viruses, put strain on the nuclear envelope as hundreds of viral DNA genomes replicate and viral capsids assemble. It remained unknown, however, how nuclear mechanics is affected at the initial stage of herpesvirus infection-immediately after viral genomes are ejected into the nuclear space-and how nucleus integrity is maintained despite an increased strain on the nuclear envelope. With an atomic force microscopy force volume mapping approach on cell-free reconstituted nuclei with docked herpes simplex type 1 (HSV-1) capsids, we explored the mechanical response of the nuclear lamina and the chromatin to intranuclear HSV-1 DNA ejection into an intact nucleus. We discovered that chromatin stiffness, measured as Young's modulus, is increased by ∼14 times, while nuclear lamina underwent softening. Those transformations could be associated with a mechanism of mechanoprotection of nucleus integrity facilitating HSV-1 viral genome replication. Indeed, stiffening of chromatin, which is tethered to the lamina meshwork, helps to maintain nuclear morphology. At the same time, increased lamina elasticity, reflected by nucleus softening, acts as a "shock absorber," dissipating the internal mechanical stress on the nuclear membrane (located on top of the lamina wall) and preventing its rupture.
当细胞暴露在机械压力下时，维持核完整性对于细胞存活至关重要。疱疹病毒与大多数 DNA 和一些 RNA 病毒一样，在数百个病毒 DNA 基因组复制和病毒衣壳组装时，会对核膜施加压力。然而，人们仍然不清楚疱疹病毒感染的初始阶段（即病毒基因组被喷射到核空间后），细胞核力学是如何受到影响的，以及尽管核膜承受的压力增加，细胞核完整性是如何得以维持的。我们采用原子力显微镜力体积映射方法，对带有停泊的单纯疱疹病毒 1（HSV-1）衣壳的无细胞重构核进行研究，探索了核纤层和染色质对 HSV-1 病毒 DNA 喷射到完整细胞核内的机械响应。我们发现，染色质的硬度（以杨氏模量衡量）增加了约 14 倍，而核纤层则变软。这些转变可能与一种保护细胞核完整性的力学保护机制有关，该机制有助于 HSV-1 病毒基因组的复制。事实上，与核纤层网格系链的染色质变硬有助于维持核形态。同时，核变软反映出的核纤层弹性增加，充当了“减震器”，可以消散核膜（位于核纤层壁顶部）上的内部机械应力，防止其破裂。
