Feldherr C M, Akin D
Department of Anatomy and Cell Biology, University of Florida, Gainesville 32610.
J Cell Biol. 1990 Jul;111(1):1-8. doi: 10.1083/jcb.111.1.1.
The objective of this study was to determine whether the permeability characteristics of the nuclear envelope vary during different phases of cellular activity. Both passive diffusion and signal-mediated transport across the envelope were analyzed during the HeLa cell cycle, and also in dividing, confluent (growth-arrested), and differentiated 3T3-L1 cultures. Colloidal gold stabilized with BSA was used to study diffusion, whereas transport was investigated using gold particles coated with nucleoplasmin, a karyophilic Xenopus oocyte protein. The gold tracers were microinjected into the cytoplasm, and subsequently localized within the cells by electron microscopy. The rates of diffusion in HeLa cells were greatest during the first and fifth hours after the onset of anaphase. These results correlate directly with the known rates of pore formation, suggesting that pores are more permeable during or just after reformation. Signal-mediated transport in HeLa cells occurs through channels that are located within the pore complexes and have functional diameters up to 230-250 A. Unlike diffusion, no significant differences in transport were observed during different phases of the cell cycle. A comparison of dividing and confluent 3T3-L1 cultures revealed highly significant differences in the transport of nucleoplasmin-gold across the envelope. The nuclei of dividing cells not only incorporated larger particles (230 A versus 190 A in diameter, including the protein coat), but the relative uptake of the tracer was about seven times greater than that in growth-arrested cells. Differentiation of confluent cells to adipocytes was accompanied by an increase in the maximum diameter of the transport channel to approximately 230 A.
本研究的目的是确定核膜的通透性特征在细胞活动的不同阶段是否会发生变化。在HeLa细胞周期以及分裂期、汇合期（生长停滞期）和分化的3T3-L1培养物中，对被动扩散和信号介导的跨膜运输进行了分析。用牛血清白蛋白稳定的胶体金来研究扩散，而用涂有核质蛋白（一种嗜核的非洲爪蟾卵母细胞蛋白）的金颗粒来研究运输。将金示踪剂显微注射到细胞质中，随后通过电子显微镜在细胞内定位。HeLa细胞中的扩散速率在后期开始后的第一小时和第五小时最快。这些结果与已知的孔形成速率直接相关，表明孔在重新形成期间或刚重新形成后通透性更高。HeLa细胞中的信号介导运输通过位于孔复合体中的通道进行，这些通道的功能直径可达230 - 250埃。与扩散不同，在细胞周期的不同阶段未观察到运输有显著差异。对分裂期和汇合期的3T3-L1培养物进行比较发现，核质蛋白 - 金跨膜运输存在高度显著差异。分裂细胞的细胞核不仅摄取更大的颗粒（直径230埃对190埃，包括蛋白外壳），而且示踪剂的相对摄取量比生长停滞细胞大约高七倍。汇合细胞向脂肪细胞的分化伴随着运输通道最大直径增加到约230埃。
