Oct 1, 1989

Fibrillar center distribution in nucleoli of PHA-stimulated human lymphocytes

Experimental Cell Research
R L Ochs, K Smetana


We have utilized acidic toluidine blue staining for RNA and immunofluorescence staining for RNA polymerase 1 to visualize the distribution of fibrillar centers (FCs) in nucleoli of PHA-stimulated human lymphocytes. At 0 h, there is a single large fibrillar center in each nucleolus which splits into smaller and more numerous FCs until the number of FCs reaches five, the number of nucleolus organizers in normal haploid human cells. With time, each FC then "unwinds" to form linear arrays of smaller FCs until the maximum number of FCs approaches the ribosomal gene copy number of 200 at 48 h in culture. It is hypothesized that in the most active state, each nucleolar FC visualized by RNA polymerase 1 staining actually represents a single transcription unit and the distance between adjacent FCs is occupied by the nontranscribed spacer region. We conclude that the number of fibrillar centers per nucleolus can be used as a direct quantitative measure of nucleolar transcriptional activity.

Mentioned in this Paper

Immunofluorescence Assay
Lymphocytes as Percentage of Blood Leukocytes (Lab Test)
DNA-Directed RNA Polymerase
RNA Polymerase Assembly Pathway
Transcription, Genetic
Tolonium chloride
Lymphocyte Activation
Electron Microscopy

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