Nucleoli fibrillar center

The nucleolar fibrillar center (FC) is a subcompartment of the nucleolus with a clear fibrillar structure, assembled around active nucleolar organizing regions (NORs) at certain chromosomal loci. Transcription of rDNA occurs at the border of fibrillar centers and the surrounding dense fibrillar component, while the fibrillar center holds the nontranscribed copies of rDNAs as well as the RNA polymerase I complexes andother parts of the transcription machinery.

Immunofluorescent staining

The nucleoli fibrillar center, and/or dense fibrillar component, can appear as a spotty cluster or as a single bigger spot in the nucleolus, depending on the cell line.

Read more about the proteome of the nucleoli fibrillar center as substructures of nucleoli.