title: Transcription-dependent rearrangements of actin and nuclear myosin I in the nucleolus.
abstract: 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.
authors.affiliation: 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.
authors.forename: V V
authors.initials: VV
authors.lastname: Philimonenko
authors.forename: J
authors.initials: J
authors.lastname: Janácek
authors.forename: M
authors.initials: M
authors.lastname: Harata
authors.forename: P
authors.initials: P
authors.lastname: Hozák
mesh_terms: D000199:Actins / Q000378:metabolism*; D002466:Cell Nucleolus / Q000378:metabolism*; D004275:DNA, Ribosomal / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D007150:Immunohistochemistry; D024461:Myosin Type I / Q000378:metabolism*; D035463:Pol1 Transcription Initiation Complex Proteins / Q000378:metabolism; D012318:RNA Polymerase I / Q000378:metabolism; D012335:RNA, Ribosomal / Q000378:metabolism; D014158:Transcription, Genetic / Q000502:physiology*
chemical_list: D000199:Actins; D004275:DNA, Ribosomal; D035463:Pol1 Transcription Initiation Complex Proteins; D012335:RNA, Ribosomal; C063844:transcription factor UBF; D012318:RNA Polymerase I; D024461:Myosin Type I