title: Reproduction of the FC/DFC units in nucleoli.
abstract: The essential structural components of the nucleoli, Fibrillar Centers (FC) and Dense Fibrillar Components (DFC), together compose FC/DFC units, loci of rDNA transcription and early RNA processing. In the present study we followed cell cycle related changes of these units in 2 human sarcoma derived cell lines with stable expression of RFP-PCNA (the sliding clamp protein) and GFP-RPA43 (a subunit of RNA polymerase I, pol I) or GFP-fibrillarin. Correlative light and electron microscopy analysis showed that the pol I and fibrillarin positive nucleolar beads correspond to individual FC/DFC units. In vivo observations showed that at early S phase, when transcriptionally active ribosomal genes were replicated, the number of the units in each cell increased by 60-80%. During that period the units transiently lost pol I, but not fibrillarin. Then, until the end of interphase, number of the units did not change, and their duplication was completed only after the cell division, by mid G1 phase. This peculiar mode of reproduction suggests that a considerable subset of ribosomal genes remain transcriptionally silent from mid S phase to mitosis, but become again active in the postmitotic daughter cells.
authors.affiliation: a Charles University in Prague , First Faculty of Medicine , Institute of Cellular Biology and Pathology , Prague , Czech Republic.
authors.forename: Evgeny
authors.initials: E
authors.lastname: Smirnov
authors.affiliation: a Charles University in Prague , First Faculty of Medicine , Institute of Cellular Biology and Pathology , Prague , Czech Republic.
authors.forename: Matúš
authors.initials: M
authors.lastname: Hornáček
authors.affiliation: a Charles University in Prague , First Faculty of Medicine , Institute of Cellular Biology and Pathology , Prague , Czech Republic.
authors.forename: Lubomír
authors.initials: L
authors.lastname: Kováčik
authors.affiliation: a Charles University in Prague , First Faculty of Medicine , Institute of Cellular Biology and Pathology , Prague , Czech Republic.
authors.forename: Tomáš
authors.initials: T
authors.lastname: Mazel
authors.affiliation: a Charles University in Prague , First Faculty of Medicine , Institute of Cellular Biology and Pathology , Prague , Czech Republic.
authors.forename: Adam
authors.initials: A
authors.lastname: Schröfel
authors.affiliation: a Charles University in Prague , First Faculty of Medicine , Institute of Cellular Biology and Pathology , Prague , Czech Republic.
authors.forename: Silvie
authors.initials: S
authors.lastname: Svidenská
authors.affiliation: a Charles University in Prague , First Faculty of Medicine , Institute of Cellular Biology and Pathology , Prague , Czech Republic.
authors.forename: Magdalena
authors.initials: M
authors.lastname: Skalníková
authors.affiliation: a Charles University in Prague , First Faculty of Medicine , Institute of Cellular Biology and Pathology , Prague , Czech Republic.|b Institute of Biophysics of the CAS , Brno , Czech Republic.
authors.forename: Eva
authors.initials: E
authors.lastname: Bartová
authors.affiliation: a Charles University in Prague , First Faculty of Medicine , Institute of Cellular Biology and Pathology , Prague , Czech Republic.
authors.forename: Dušan
authors.initials: D
authors.lastname: Cmarko
authors.affiliation: a Charles University in Prague , First Faculty of Medicine , Institute of Cellular Biology and Pathology , Prague , Czech Republic.
authors.forename: Ivan
authors.initials: I
authors.lastname: Raška
mesh_terms: D002466:Cell Nucleolus / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D016196:S Phase
keywords: FC/DFC units; cell cycle; nucleolus; rDNA; replication