In human cells ribosomal genes are organized as clusters, NORs, situated on the short arms of acrocentric chromosomes. It was found that essential components of the RNA polymerase I transcription machinery, including UBF, can be detected on some NORs, termed "competent" NORs, during mitosis. The competent NORs are believed to be transcriptionally active during interphase. However, since individual NORs were not observed in the cell nucleus, their interphase status remains unclear. To address this problem, we detected the competent NORs by two commonly used methods, UBF immunofluorescence and silver staining, and combined them with FISH for visualization of rDNA and/or specific chromosomes. We found that the numbers of competent NORs on specific chromosomes were largely conserved in the subsequent cell cycles, with certain NOR-bearing homologues displaying a very stable pattern of competence. Importantly, those and only those NORs that were loaded with UBF incorporated bromo-uridine in metaphase after stimulation with roscovitine and in telophase, suggesting that competent and only competent NORs contain ribosomal genes transcriptionally active during interphase. Applying premature chromosome condensation with calyculin A, we visualized individual NORs in interphase cells, and found the same pattern of competence as observed in the mitotic chromosomes.

• MeSH
• Silver Staining MeSH
• Cell Cycle * drug effects   MeSH
• Transcription, Genetic * drug effects   MeSH
• HeLa Cells MeSH
• In Situ Hybridization, Fluorescence MeSH
• Interphase drug effects   MeSH
• Karyotyping MeSH
• Humans MeSH
• Chromosomes, Human genetics   MeSH
• Metaphase drug effects   MeSH
• Nucleolus Organizer Region drug effects   genetics   MeSH
• Purines pharmacology   MeSH
• Roscovitine MeSH
• Telophase drug effects   MeSH
• Pol1 Transcription Initiation Complex Proteins metabolism   MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Purines MeSH
• Roscovitine MeSH
• transcription factor UBF MeSH Browser
• Pol1 Transcription Initiation Complex Proteins MeSH

Early leukemic granulocytic and plasmacytic precursors were studied in vitro and in vivo to provide an information on the intranucleolar distribution of AgNORs (silver stained nucleolus organizer regions). In most of these cells AgNORs appeared as clusters of silver stained particles distributed in the whole nucleolar body. On the other hand, in some leukemic early granulocytic precursors, i.e., in myeloblasts and promyelocytes enlarged AgNORs were translocated in the nucleolar peripheral part. In addition, the number of translocated AgNORs at the nucleolar periphery was significantly smaller. Such translocation of a reduced number of AgNORs was easily produced by experimental aging, i.e., starving of cultured leukemic early granulocytic precursors (HL-60 and K562 cells) in vitro and seems to be reversible. Similar translocation of a reduced number of AgNORs was also produced by aging of leukemic plasmacytic precursors. Thus, the translocation of the reduced number of AgNORs to the nucleolar periphery in some blastic leukemic hematopoietic cells might be an useful marker of their aging at the single cell level. However, more studies in this direction are required in the future.

• MeSH
• Silver Staining MeSH
• Cell Nucleolus metabolism   MeSH
• Cell Cycle physiology   MeSH
• K562 Cells MeSH
• Bone Marrow Cells metabolism   MeSH
• DNA, Neoplasm metabolism   MeSH
• Granulocytes metabolism   ultrastructure   MeSH
• HL-60 Cells MeSH
• Leukemia metabolism   MeSH
• Humans MeSH
• Nucleolus Organizer Region metabolism   MeSH
• Plasma Cells metabolism   ultrastructure   MeSH
• RNA, Neoplasm metabolism   MeSH
• Cellular Senescence physiology   MeSH
• Protein Transport MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• DNA, Neoplasm MeSH
• RNA, Neoplasm MeSH