Direct Visualization of a Protein Nuclear Architecture

Whether the cell nucleus is organized by an underlying architecture analagous to the cytoskeleton has been a highly contentious issue since the original isolation of a nuclease and salt-resistant nuclear matrix. Despite electron microscopy studies that show that a nuclear architecture can be visualized after fractionation, the necessity to elute chromatin to visualize this structure has hindered general acceptance of a karyoskeleton. Using an analytical electron microscopy method capable of quantitative elemental analysis, electron spectroscopic imaging, we show that the majority of the fine structure within interchromatin regions of the cell nucleus in fixed whole cells is not nucleoprotein. Rather, this fine structure is compositionally similar to known protein-based cellular structures of the cytoplasm. This study is the first demonstration of a protein network in unfractionated and uninfected cells and provides a method for the ultrastructural characterization of the interaction of this protein architecture with chromatin and ribonucleoprotein elements of the cell nucleus.

自首次分离出核酸酶与耐盐核基质以来，细胞核是否由类似于细胞骨架（cytoskeleton）的底层架构组织而成，始终是一个极具争议的学术议题。尽管已有电子显微镜研究证实，经分级分离后可观测到核架构，但由于可视化该结构需要洗脱染色质，这一问题阻碍了核骨架（karyoskeleton）概念的广泛认可。我们采用可实现定量元素分析的分析型电子显微镜方法——电子光谱成像（electron spectroscopic imaging），证实：在固定的完整细胞的细胞核染色质间区域内，绝大多数精细结构并非核蛋白。与之相反，该精细结构的组成与细胞质中已知的基于蛋白质的细胞结构高度相似。本研究首次在未分级分离且未受感染的细胞中证实了蛋白质网络的存在，并为该蛋白质架构与细胞核内染色质及核糖核蛋白（ribonucleoprotein）元件的相互作用的超微结构表征提供了方法。