Shemyakin and Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences.
Acta Naturae. 2011 Oct;3(4):100-6.
Nucleolus is the major structural domain of the cell nucleus, which in addition to proteins contains ribosomal RNA (rRNA) at different stages of maturation (or pre-rRNA). In mammals, the onset of mitosis is accompanied by the inhibition of rRNA synthesis, nucleolus disassembly, and the migration of pre-rRNA to the cytoplasm. However, the precise role of cytoplasmic pre-rRNA in mitosis remains unclear, and no comparative analysis of its different forms at consequent mitotic stages has thus far been performed. The focus of this research was the study of the localization of pre-rRNA in mitotic NIH/3T3 mouse fibroblasts by fluorescentin situhybridization (FISH) with probes to several regions of mouse primary 47S pre-rRNA transcripts and by confocal laser microscopy. The results reveal that all types of pre-rRNA appear in the cytoplasm at the beginning of mitosis, following the breakdown of the nucleolus and nuclear envelope. However, not all pre-rRNA are transported by chromosomes from maternal cells into daughter cells. At the end of mitosis, all types of pre-rRNA and 28S rRNA can be visualized in nucleolus-derived foci (NDF), structures containing many proteins of mature nucleoli the appearance of which indicates the commencement of nucleologenesis. However, early NDF are enriched in less processed pre-RNA, whereas late NDF contain predominantly 28S rRNA. Altogether, the results of this study strengthen the hypotheses that postulate that different forms of pre-rRNA may play various roles in mitosis, and that NDF can be involved in the maturation of pre-rRNA, remaining preserved in the cytoplasm of dividing cells.
核仁是细胞核的主要结构域，除了蛋白质外，还含有处于不同成熟阶段（或前 rRNA）的核糖体 RNA（rRNA）。在哺乳动物中，有丝分裂的开始伴随着 rRNA 合成的抑制、核仁解体以及前 rRNA 向细胞质的迁移。然而，细胞质前 rRNA 在有丝分裂中的精确作用尚不清楚，而且迄今尚未对其在随后的有丝分裂阶段的不同形式进行比较分析。本研究的重点是通过荧光原位杂交（FISH）用针对小鼠初级 47S 前 rRNA 转录物的几个区域的探针研究有丝分裂 NIH/3T3 小鼠成纤维细胞中前 rRNA 的定位，并用共聚焦激光显微镜进行研究。结果表明，所有类型的前 rRNA 在前核仁体和核膜破裂后，在有丝分裂开始时出现在细胞质中。然而，并非所有前 rRNA 都通过染色体从母细胞运送到子细胞中。在有丝分裂末期，可以在核仁衍生的焦点（NDF）中观察到所有类型的前 rRNA 和 28S rRNA，这些结构包含成熟核仁的许多蛋白质，其出现表明核仁发生的开始。然而，早期的 NDF 富含未加工的前 RNA，而晚期的 NDF 则主要包含 28S rRNA。总的来说，这项研究的结果加强了假设，即假定不同形式的前 rRNA 可能在有丝分裂中发挥不同的作用，并且 NDF 可以参与前 rRNA 的成熟，并保留在分裂细胞的细胞质中。
