The Ag-NOR proteins and transcription and duplication of ribosomal genes in mammalian cell nucleoli.
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.
Pession
A
A
Dipartimento di Patologia Sperimentale, Università di Bologna, Italy.
Farabegoli
F
F
Treré
D
D
Novello
F
F
Montanaro
L
L
Sperti
S
S
Rambelli
F
F
Derenzini
M
M
D000818:Animals; D002453:Cell Cycle; D004247:DNA / Q000096:biosynthesis; D008099:Liver / Q000166:cytology / Q000648:ultrastructure; D008115:Liver Regeneration; D008854:Microscopy, Electron; D005810:Multigene Family; D009687:Nuclear Proteins / Q000235:genetics*; D009697:Nucleolus Organizer Region / Q000378:metabolism* / Q000648:ultrastructure; D012335:RNA, Ribosomal / Q000096:biosynthesis*; D051381:Rats; D011919:Rats, Inbred Strains; D012834:Silver; D013194:Staining and Labeling; D014158:Transcription, Genetic
D009687:Nuclear Proteins; D012335:RNA, Ribosomal; D012834:Silver; D004247:DNA