Dense fibrillar component

Close observations of immunofluorescence signals showed that there are three different staining patterns, which correspond to three different nucleolar compartments FC (Fibrillar center), DFC (dense fibrillar component), and GC (granular component). Nucleolus is surrounded by heterochromatin. When the cells are in very active state of its proliferation, the nucleolar compartments and heterochromatin are integrated into a highly intricate structure called nucleolonema . A recent study has suggested that the chromatin associated with the nucleolus is less mobile than... 

Fig.l Electron micrograph of an interphase nucleolus illustrating the component parts of fibrillar center (FC), dense fibrillar component (DFC), and granular component (GC). Scale bar, 0.5 /um. 

Fig. 5 Antibody labeling of nucleolar component parts by iromunoelectron microscopy (a, c, and e) and indirect immunofluorescence (b, d, and f). (a and b) Fibrillar centers (FC) labeled with antibody to RNA polymerase I. (c and d) Dense fibrillar component (DFC) labeled with antibody to fibrillarin. (e and f) Granular component (GC) labeled with antibody to protein B23. (a, c, and e) Scale bar, 0.5 /urn. (b, d, and f) Scale bar, 5 /im.

The dense fibrillar component is thought to be the structural equivalent of the site of synthesis of the ribosomal RNA (Raska et al, 1990b Hozak et al. 

Fig. 7 Electron microscopy of segregated nucleoli from cells treated with 0.1 jug/ml actinomycin D (a) or 25 /ig/ml DRB (b) for 4 hr. FC, Fibrillar center DFC, dense fibrillar component GC, granular component. Arrowhead (b) denotes a (ibrillar center. Scale bar, 0.5 tm.

Raska, 1., Dundr, M., Koberna, K., Melcak, 1., Risueno, M., and Torok, 1. (1995). Does the synthesis of ribosomal RNA take place within nucleolar fibrillar centers or dense fibrillar components A critical appraisal. J. Struct. BioL 114,1-22. 

Antifibrillarin 34-kDa fibrillarin Dense fibrillar component of nucleolus... 

Intermediate filaments are about lOnm in diameter, and are more stable (strongly bound) than actin filaments. Like actin filaments they function in the maintenance of cell shape by bearing tension. Intermediate filaments organise the internal tridimensional structure of the ceU, anchoring organelles and serving as structural components of the nuclear lamina (a dense fibrillar network inside the nucleus) and sarcomeres. They also participate in some cell-cell and cell-matrix junctions. 

Fig. 6 Distribution of flbrillar centers in PHA-stimulated human lymphocytes at 0 (a and d), 24 (b and e), and 48 hr (c and f) as visualized by conventional electron microscopy (a-c) and by indirect immunofluorescence (d-f) using a human autoantibody to RNA polymerase I. FC, Fibrillar center, DFC, dense flbrillar component G, granular component. The resting, unstimulated lymphocyte (a and d) contains a single large FC (arrowhead in d) that increases in number and decreases in size as the nucleolus grows in size with continued stimulation, (a-c) Scale bar, 0.5 /zm. (d-f) Scale bar, 5 /i.m.

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