Initiation of nucleolar assembly is independent of RNA polymerase I transcription
Initiation of nucleolar assembly is independent of RNA polymerase I transcription
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DOI：
10.1091/mbc.11.8.2705
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发表时间：
2000-08-01
影响因子：
3.3
通讯作者：
Huang, S
中科院分区：
文献类型：
--
作者：
Dousset, T;Wang, C;Huang, S
本报告检查了 HeLa 细胞中 RNA 聚合酶 I 转录因子（上游结合因子；UBF）、前 rRNA 加工因子（核仁素和原纤维蛋白）和前 rRNA 在整个有丝分裂和有丝分裂后核发生过程中的分布。结果表明，在前一个细胞周期的 G2/M 期合成的核仁素、原纤维蛋白和前 rRNA 在染色体解凝之前的末期早期直接被招募到 UBF 相关的核仁组织区 (NOR)。与核仁前体与核仁的融合不同，加工因子和前 rRNA 的早期募集独立于 RNA 聚合酶 I 转录。在缺乏聚合酶 I 转录的情况下，核仁蛋白、原纤维蛋白和前 rRNA 最初定位到 UBF 相关 NOR 中会产生分离的小核仁，类似于在相同条件下生长的间期细胞中观察到的较大核仁。 Pre-rRNA 与 UBF-核仁素-原纤维帽并列，可能代表电子显微镜观察到的分离的核仁。这些发现导致了核发生模型的修订。我们认为，有丝分裂末期的核仁形成是由于在 rDNA 转录之前或开始时将加工因子和 pre-rRNA 直接募集到 UBF 相关 NOR 的结果。随后将预先包装的核仁前体融合到核仁中。在先前的细胞周期中合成的前核糖体核糖核蛋白可能有助于有丝分裂后核发生。
This report examines the distribution of an RNA polymerase I transcription factor (upstream binding factor; UBF), pre-rRNA processing factors (nucleolin and fibrillarin), and pre-rRNAs throughout mitosis and postmitotic nucleologenesis in HeLa cells. The results demonstrate that nucleolin, fibrillarin, and pre-rRNAs synthesized at G2/M phase of the previous cell cycle are directly recruited to UBF-associated nucleolar organizer regions (NORs) early in telophase before chromosome decondensation. Unlike the fusion of prenucleolar bodies to the nucleoli, this early recruitment of processing factors and pre-rRNAs is independent of RNA polymerase I transcription. In the absence of polymerase I transcription, the initial localization of nucleolin, fibrillarin, and pre-rRNAs to UBF-associated NORs generates segregated mininucleoli that are similar to the larger ones observed in interphase cells grown under the same conditions. Pre-rRNAs are juxtaposed to UBF-nucleolin-fibrillarin caps that may represent the segregated nucleoli observed by electron microscopy. These findings lead to a revised model of nucleologenesis. We propose that nucleolar formation at the end of mitosis results from direct recruitment of processing factors and pre-rRNAs to UBF-associated NORs before or at the onset of rDNA transcription. This is followed by fusion of prepackaged prenucleolar bodies into the nucleolus. Pre-ribosomal ribonucleoproteins synthesized in the previous cell cycle may contribute to postmitotic nucleologenesis.