The giant fibrillar center: a nucleolar structure enriched in upstream binding factor (UBF) that appears in transcriptionally more active sensory ganglia neurons.
This paper studies the molecular organization, neuronal distribution and cellular differentiation dynamics of the giant fibrillar centers (GFCs) of nucleoli in rat sensory ganglia neurons. The GFC appeared as a round nucleolar domain (1-2 microm in diameter) partially surrounded by the dense fibrillar component and accompanied by numerous small FCs. By immunocytochemistry, the GFC concentrated the upstream binding factor, which may serve as a marker of this structure, and also contain RNA polymerase I, DNA topoisomerase I, SUMO-1 and Ubc9. However, they lack ubiquitin-proteasome conjugates and 20S proteasome. Transcription assay with 5'-fluorouridine incorporation revealed the presence of nascent RNA on the dense fibrillar component of the neuronal nucleolus, but not within the low electron-density area of the GFC. The formation of GFCs is neuronal size dependent: they were found in 58%, 30% and 0% of the large, medium and small neurons, respectively. GFCs first appeared during the postnatal period, concomitantly with a stage of neuronal growth, myelination and bioelectrical maturation. GFCs were not observed in segregated nucleoli induced by severe inhibition of RNA synthesis. We suggest that the formation of GFCs is associated with a high rate of ribosome biogenesis of the transcriptionally more active large-size neurons.
Casafont
Iñigo
I
Department of Anatomy and Cell Biology, and Biomedicine Unit, CSIC, University of Cantabria, Avd. Cardenal Herrera Oria s/n, 39011 Santander, Spain.
Bengoechea
Rocio
R
Navascués
Joaquín
J
Pena
Emma
E
Berciano
Maria T
MT
Lafarga
Miguel
M
D000818:Animals; D002454:Cell Differentiation; D002466:Cell Nucleolus / Q000737:chemistry / Q000648:ultrastructure*; D017950:Ganglia, Sensory / Q000254:growth & development* / Q000378:metabolism / Q000648:ultrastructure*; D008297:Male; D016253:Microscopy, Immunoelectron; D009475:Neurons, Afferent / Q000378:metabolism / Q000648:ultrastructure*; D035463:Pol1 Transcription Initiation Complex Proteins / Q000032:analysis*; D046988:Proteasome Endopeptidase Complex / Q000032:analysis / Q000378:metabolism; D012335:RNA, Ribosomal / Q000032:analysis / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D025842:SUMO-1 Protein / Q000032:analysis / Q000378:metabolism; D014158:Transcription, Genetic; D025801:Ubiquitin / Q000032:analysis / Q000378:metabolism
D035463:Pol1 Transcription Initiation Complex Proteins; D012335:RNA, Ribosomal; D025842:SUMO-1 Protein; D025801:Ubiquitin; C063844:transcription factor UBF; D046988:Proteasome Endopeptidase Complex