The Ag-NOR proteins and transcription and duplication of ribosomal genes in mammalian cell nucleoli

• Published in: Chromosoma 1991-05, Vol.100 (4), p.242-250
• Main Authors: PESSION, A, FARABEGOLI, F, TRERE, D, NOVELLO, F, MONTANARO, L, SPERTI, S, RAMBELLI, F, DERENZINI, M
• Format: Article
• Language: English
• Subjects: Animals; Biological and medical sciences; Cell Cycle; Cytogenetics; DNA - biosynthesis; Fundamental and applied biological sciences. Psychology; Genetics of eukaryotes. Biological and molecular evolution; Liver - cytology; Liver - ultrastructure; Liver Regeneration; Microscopy, Electron; Multigene Family; Nuclear Proteins - genetics; Nucleolus Organizer Region - metabolism; Nucleolus Organizer Region - ultrastructure; Rats; Rats, Inbred Strains; RNA, Ribosomal - biosynthesis; Silver; Staining and Labeling; Transcription, Genetic; Vertebrata
• ISSN: 0009-5915; 1432-0886
• DOI: 10.1007/bf00344158

The relationship between the Ag-NOR (silver-stained Nucleolar Organizer Region) proteins and the functional-structural organization of the nucleolar ribosomal chromatin was studied in regenerating and cortisol-stimulated rat hepatocytes. Statistical analysis of Ag-NOR proteins, carried out with an automated image analyzer, indicated that in regenerating rat hepatocytes the quantity of Ag-NOR proteins mainly increased between the 4th and 12th h of regeneration, reaching a level twice that of resting hepatocytes. Also the synthesis of pre-ribosomal RNA (pre-rRNA) was stimulated after the 4th h of regeneration. Cycloheximide administered to rats at a dose of 0.025 mg/100 g body weight (bw) prevented any increase in Ag-NOR proteins but did not hinder the stimulation of pre-rRNA synthesis. In 8 h cortisol-stimulated hepatocytes no significant change in amount of Ag-NOR protein was observed whereas pre-rRNA synthesis was highly increased as in 12 h regenerating hepatocytes. These results indicated that in rat hepatocytes Ag-NOR proteins and stimulation of pre-rRNA synthesis are not related. The relationship between the Ag-NOR proteins and the distribution of the completely extended intranucleolar ribosomal chromatin was also studied in regenerating rat hepatocytes. At 12 h after partial hepatectomy an increased amount of completely extended ribosomal chromatin was observed, contemporaneously with an increased quantity of Ag-NOR proteins. These ribosomal chromatin changes preceded the beginning of DNA synthesis and were prevented by cycloheximide-induced inhibition of protein synthesis.