Location of rRNA Transcription to the Nucleolar Components: Disappearance of the Fibrillar Centers in Nucleoli of Regenerating Rat Hepatocytes

Abstract

ABSTRACT. The precise location of rDNA transcription to the components of mammalian cell nucleolus is still debated. This was due to the fact that all the molecules necessary for rRNA synthesis are located in two of the three components, the fibrillar centers (FCs) and the dense fibrillar component (DFC), which together with the granular component (GC) are considered to be constantly present in mammalian cell nucleoli. In the present study we demonstrated that in nucleoli of many regenerating rat hepatocytes at 15 h after partial hepatectomy the FCs were no longer present, only the DFC and the GC being detected. At this time of regeneration the rRNA transcriptional activity was three fold that of resting hepatocytes, while the synthesis of DNA was not yet significantly increased, indicating that these nucleolar changes were due to the rRNA synthesis up-regulation. The DFC appeared to be organized in numerous, small, roundish tufts of fibrils. The silver staining procedure for AgNOR proteins, which are associated with the ribosomal genes, selectively and homogeneously stained these fibrillar tufts. Immuno-gold visualization of the Upstream Binding Factor (UBF), which is associated with the promoter region and the transcribed portion of the rRNA 45S gene, demonstrated that UBF was selectively located in the fibrillar tufts. We concluded that in proliferating rat hepatocytes the increased synthesis of rRNA induced an activation of the rRNA transcription machinery located in the fibrillar centers which, by becoming associated with the ribonucleoprotein transcripts, assumed the morphological pattern of the DFC.

Visualization of the Nucleolus Using Ethynyl Uridine

“…This EU distribution seems to reflect compartmentalization of the processes in the nucleolus. Pre-rRNA is mostly transcribed at the periphery of the fibrillar centers, while fibrillarin occurs in the dense fibrillar component (see e.g., Jordan, 1984 ; Ochs et al, 1985 ; Beven et al, 1995 ; de Carcer and Medina, 1999 ; Raska et al, 2006 ; Montanaro et al, 2011 ).…”

Basic concepts of epigenetics

“…153 In euchromatin, abundant ribosomal unit transcription factories called nucleoli are easily visualized, which synthesize ribosomal subunit proteins that will be assembled later into the small and large subunits of ribosomes. 67,154 Heterochromatin and lamins. Silenced heterochromatin is comprised of two categories.…”

Sodium butyrate inhibits platelet‐derived growth factor‐induced proliferation and migration in pulmonary artery smooth muscle cells through Akt inhibition

“…After being washed, cells were finally dehydrated and mounted in a synthetic medium with no counterstaining. AgNOR analysis was carried out with IMAGE-PRO PLUS, as previously reported [34]. For each experimental condition, AgNOR intensely stained nucleolar and nuclear areas of at least 60 nuclei were measured, and the results were expressed as mean na/Na ratio normalized to control.…”