Zatsepina O V, Dudnic O A, Chentsov Y S, Thiry M, Spring H, Trendelenburg M F
A.N. Belozersky Institute of Physical and Chemical Biology, Moscow State University, Russia.
Exp Cell Res. 1997 May 25;233(1):155-68. doi: 10.1006/excr.1997.3556.
In order to determine the most persistent components of the nucleolus that might serve as "core" nucleolar elements, we studied the reactivity of nucleoli in living mammalian cells subjected to hypotonic buffer saline followed by the incubation of the cells in an isotonic medium. To document as precisely as possible the fine structural changes which occurred, the cells were examined by video-enhanced optical microscopy, fluorescence confocal laser scanning microscopy, and electron microscopy combined with cytochemistry. Light microscopic autoradiography was used to demonstrate the transcriptional characteristics of the reassembled nucleoli. It was shown that all the major compartments of the intact nucleolus could be substantially affected by reduction of the osmolarity of the environmental media. The dynamic events of the nucleolar unraveling in low-salt buffers occurred in the following order: dispersion of the nucleolar pars granulosa, disassociation of the fibrillar complexes into discrete fibrillar centers (FCs) and the dense fibrillar component (DFC), and the almost complete unraveling of the DFC and FCs. At the terminal stages of nucleolar dispersion, the nuclear interior was mainly composed of a loose filamentous meshwork, and none of the typically discerned nucleolar constituents was recognized. Nevertheless, when hypotonically treated cells were returned to isotonic conditions, the nucleolar bodies rapidly began to reassemble. Within 1-2 h of cell incubation under isotonicity, the nucleoli not only became clearly visible, but also reconstituted to their initial size, shape, and position within the nucleus. The ultrastructure and functional activity of the reassembled nucleoli were also found to be fully comparable to those of the untreated controls. These data indicate that the architectural composition of the interphase nucleolus is strictly controlled by the cell. As far as could be determined, none of the usual substructures of the intact nucleolus that could be substituted by complete reassembly of the nucleolar bodies in normotonic conditions, including FCs and the DFC, remained clearly preserved in the terminal stage of nucleolar unraveling. We concluded that the integrity of the nucleolus was mainly preserved by the nuclear or nucleolar matrix system rather than by any other nucleolar structural domains.
为了确定核仁中可能作为“核心”核仁元件的最持久成分，我们研究了在低渗缓冲盐溶液处理后的活哺乳动物细胞中核仁的反应性，随后将细胞置于等渗培养基中孵育。为了尽可能精确地记录所发生的精细结构变化，通过视频增强光学显微镜、荧光共聚焦激光扫描显微镜以及结合细胞化学的电子显微镜对细胞进行检查。光镜放射自显影用于证明重新组装的核仁的转录特征。结果表明，完整核仁的所有主要部分都可能受到环境介质渗透压降低的显著影响。在低盐缓冲液中核仁解聚的动态事件按以下顺序发生：颗粒区的分散、纤维复合体解离为离散的纤维中心（FCs）和致密纤维成分（DFC），以及DFC和FCs几乎完全解聚。在核仁分散的末期，核内主要由松散的丝状网络组成，没有任何典型可辨别的核仁成分。然而，当低渗处理的细胞恢复到等渗条件时，核仁体迅速开始重新组装。在等渗条件下细胞孵育1 - 2小时内，核仁不仅清晰可见，而且在核内重新形成其初始大小、形状和位置。重新组装的核仁的超微结构和功能活性也被发现与未处理的对照完全相当。这些数据表明，间期核仁的结构组成受到细胞的严格控制。据测定，在等渗条件下核仁体完全重新组装可以替代的完整核仁的任何常见亚结构，包括FCs和DFC，在核仁解聚的末期都没有明显保留。我们得出结论，核仁的完整性主要由核或核仁基质系统维持，而不是由任何其他核仁结构域维持。
