Department of Biology of the Cell Nucleus, Institute of Molecular Genetics of the AS CR, v.v.i., Vídenská 1083, 142 20 Prague 4, Czech Republic.
Histochem Cell Biol. 2010 Sep;134(3):243-9. doi: 10.1007/s00418-010-0732-8. Epub 2010 Aug 4.
Nuclear actin and nuclear myosin I (NMI) are important players in transcription of ribosomal genes. Transcription of rDNA takes place in highly organized intranuclear compartment, the nucleolus. In this study, we characterized the localization of these two proteins within the nucleolus of HeLa cells with high structural resolution by means of electron microscopy and gold-immunolabeling. We demonstrate that both actin and NMI are localized in specific compartments within the nucleolus, and the distribution of NMI is transcription-dependent. Moreover, a pool of NMI is present in the foci containing nascent rRNA transcripts. Actin, in turn, is present both in transcriptionally active and inactive regions of the nucleolus and colocalizes with RNA polymerase I and UBF. Our data support the involvement of actin and NMI in rDNA transcription and point out to other functions of these proteins in the nucleolus, such as rRNA maturation and maintenance of nucleolar architecture.
核纤层蛋白和核肌球蛋白 I（NMI）是核糖体基因转录的重要参与者。rDNA 的转录发生在高度组织化的核内区室——核仁中。在这项研究中，我们通过电子显微镜和金免疫标记，以高结构分辨率对这两种蛋白质在 HeLa 细胞核仁中的定位进行了表征。我们证明，肌动蛋白和 NMI 都定位于核仁内的特定隔室中，并且 NMI 的分布依赖于转录。此外，在含有新生 rRNA 转录本的焦点中存在 NMI 池。反过来，肌动蛋白存在于核仁转录活跃和不活跃的区域，并与 RNA 聚合酶 I 和 UBF 共定位。我们的数据支持肌动蛋白和 NMI 参与 rDNA 转录，并指出这些蛋白质在核仁中的其他功能，例如 rRNA 成熟和核仁结构的维持。
