Laboratory of Biomechanics, Institute for Life and Medical Sciences, Kyoto University, 53 Shogoin-Kawahara, Sakyo, Kyoto 606-8507, Japan.
Department of Micro Engineering, Graduate School of Engineering, Kyoto University, 53 Shogoin-Kawahara, Sakyo, Kyoto 606-8507, Japan.
J Cell Sci. 2024 Oct 15;137(20). doi: 10.1242/jcs.262039. Epub 2024 Oct 4.
In eukaryotic cell nuclei, specific sets of proteins gather in nuclear bodies and facilitate distinct genomic processes. The nucleolus, a nuclear body, functions as a factory for ribosome biogenesis by accumulating constitutive proteins, such as RNA polymerase I and nucleophosmin 1 (NPM1). Although in vitro assays have suggested the importance of liquid-liquid phase separation (LLPS) of constitutive proteins in nucleolar formation, how the nucleolus is structurally maintained with the intranuclear architecture remains unknown. This study revealed that the nucleolus is encapsulated by a single-stranded (ss)DNA-based molecular complex inside the cell nucleus. Super-resolution lattice-structured illumination microscopy (lattice-SIM) showed that there was a high abundance of ssDNA beyond the 'outer shell' of the nucleolus. Nucleolar disruption and the release of NPM1 were caused by in situ digestion of ssDNA, suggesting that ssDNA has a structural role in nucleolar encapsulation. Furthermore, we identified that ssDNA forms a molecular complex with histone H1 for nucleolar encapsulation. Thus, this study illustrates how an ssDNA-based molecular complex upholds the structural integrity of nuclear bodies to coordinate genomic processes such as gene transcription and replication.
在真核细胞核中，特定的蛋白质集合在核体内，促进不同的基因组过程。核仁是一个核体，通过积累组成性蛋白质，如 RNA 聚合酶 I 和核仁磷酸蛋白 1（NPM1），作为核糖体生物发生的工厂。尽管体外实验表明组成性蛋白质的液-液相分离（LLPS）在核仁形成中的重要性，但核仁如何与核内结构保持结构上的维持仍然未知。本研究揭示了核仁被细胞核内的基于单链（ss）DNA 的分子复合物所包裹。超分辨率晶格结构照明显微镜（lattice-SIM）显示，核仁“外壳”之外有大量的 ssDNA。核仁的破坏和 NPM1 的释放是由 ssDNA 的原位消化引起的，这表明 ssDNA 在核仁包裹中具有结构作用。此外，我们确定 ssDNA 与组蛋白 H1 形成一个分子复合物来包裹核仁。因此，本研究说明了基于 ssDNA 的分子复合物如何维持核体内的结构完整性，以协调基因转录和复制等基因组过程。
