Alterations of three-dimensional structure of nucleolar organizers during cell division and differentiation

用光学显微镜和电子显微镜对萝卜根尖细胞的核仁进行了研究，特别是对其三维结构进行了研究。它的轮廓非常复杂，风干样品的厚度变化很大。它通常看起来像是卷曲或蜿蜒。核仁连续超薄切片的纵向取向首先显示出一堆短的核仁碎片，然后是一对中间有间隙的有节的框架，再是一堆短的核粒碎片。横断面随着开口方向的变化呈“C”字形。形态计量学结果表明，核仁有两种类型，平均厚度分别为510 nm和1.19微米。细的核粒体合在一起，可以卷曲或折叠形成厚的核粒体核。包括dna结构在内的纤维中心与薄核…密切相关。在低氧条件下，洋葱核仁内DNA的定位被观察到。用浸银技术对连续超薄切片的研究表明，核仁分成两个区域，即致密纤维组分(DFC)的中心核心和颗粒组分(GC)的外围，并在DEC核心内形成了游荡的消色通道。电子显微镜显示，消色通道的QcCurrent是由纤维中心(FCs)的发展和/或融合引起的，FCs被认为含有暂时休眠的核糖体-RNA基因(RDNA)。抗DNA抗体标记的DFC明显强于胞浆，标记的特异性在整个DC中是一致的。有趣的是，低氧条件下内皮细胞及其周围区域的标记特异性与正常培养的几乎相同。在低氧条件下，伴随着FCS的发育，FCS内形成了直径约35微米的颗粒(35 Nm)。它们根本没有被抗DNA抗体和核糖核酸酶-金复合体标记，表明它们既不含有DNA，也不含有RNA。总之，当细胞暴露在低氧条件下时，含有可能参与RNA转录的核仁内DNA的DFC可能会逐渐崩塌，变成FCS，同时释放灭活的rDNA，形成染色质样核团和Sonic核仁蛋白，形成35inn颗粒。较少

The nucleoloneina of Raphanus sativus root-tip cells was studied with light and electron microscopy especially focusing on its three-dimensional structural organization. Its countour was very intricate and thc thickness showed a large variation in air-dried specimens. It usually appeared to coil or meander. Serial ultrathin sectioning of thc nucleolonema iii its longitudinal orientation first revealed the stack of short nucleolonema fragments, then a pair of knobbly frames with space in-between, and again the stack of the short nucleolonema segments. On the other hand, transversal sections revealed 'c'-shaped segments with the change of their openings' orientation. Morphometry of the nucleolonema indicated two categories of the nucleolonema ; each had an average thickness of 510 nm and 1.19mum, respectively. Taken together, the thin nucleolonema may coil or fold to form the thick one. The fibrillar centers including DNA-containing structures were closely associated with the thin nucleo … More lonem a and intermittently arranged along the nucleolonema.Localization of intranucleolar DNA under hypoxic conditions was examined in excised loot tips of Allium cepa. Application of a silver impregnation technique to serial ultrathin sections indicated that the nucleolus segregated into two regions, the central core of the dense fibrillar component (DFC) and the periphery of the granular component (GC), and developed achromatic channels meandering within the DEC core. Electron microscopy showed that the Qccurrence of the achromatic channel was caused by development and/or fusion of the fibrillar centers (FCs), which are believed to contain the temporarily resting ribosomal-RNA genes (rDNA). The label of the DFC with anti-DNA antibodies was significantly strong compared with that of the cytosol and the labeling specificity was uniform throughout the DEC.Interestingly, the labeling specificity of the ECs and their surrounding region in the specimens exposed to hypoxic condition was almost the same as those grown under a normal condition. Concurrently with the development of the FCs under hypoxic conditions, the granules about 35 um in diameter (35 nm granules) were formed in the FCs. They were not labeled at all with anti-DNA antibodies and RNase-gold complexes, indicating that they contain neither DNA nor RNA.Altogether, the DFC containing the intranucleolar DNA probably engaged in the RNA transcription may gradually collapses to turn into the FCs and simultaneously releases the inactivated rDNA as clusters of chromatin-likemasses and Sonic nucleolar proteins as the 35 inn granules, when the cells are exposed to hypoxic conditions. Less