Identification and Definition of nucleolus-related fibrillar bodies in micronucleated cells

Abstract

Small nucleolus-related bodies which occur in the nUcleoplasm of " micronuclei " lacking nucleolar organizers have been studied by immunofluorescence microscopy . These bodies stained specifically with three different antibodies directed against proteins that are normally associated with the dense fibrillar component of functional nucleoli, but not with antibodies specific for certain proteins of the granular component or the fibrillar centers . Our data show that, in the absence of rRNA genes , the various constituent proteins characteristic of the dense fibrillar component spontaneously assemble into spherical entities but that the subsequent fusion of these bodies into larger structures is prevented in these micronuclei . The similarity between these nucleolus-related bodies of micronuclei and the prenucleolar bodies characteristic of early stages of nucleologenesis during mitotic telophase is discussed.

Colocalization of coilin and nucleolar proteins in Cajal body-like structures of micronucleated PtK2 cells

“…The detection of NOR-90/hUBF in the round bodies of nucleolus-devoid micronuclei agrees with previous reports that proteins of the DFC nucleolar region such as fibrillarin gather in nuclear aggregates (dots) in micronuclei devoid of rRNA genes (24). Fibrillarin is found in the nucleolus at the interface between DFC and FC and is also detected in CB (16).…”

“…In a previous study on micronucleated PtK 2 cells, Benavente et al (24) could not detect RNA polymerase I in the round structures present in micronuclei devoid of NOR. In contrast, Hernandez-Verdun et al (25), using antisera against nucleolar proteins localized in FC, DFC, and GC regions, reported that FC antigens could be detected in variable amounts in the dots of micronucleated PtK 1 cells.…”

“…Earlier studies have shown that NOR-devoid PtK 2 micronuclei present nucleolus-related fibrillar bodies or dots (24,25). These bodies were not recognized by anti-RNA polymerase I antibodies but reacted with antiserum against fibrillarin and with a monoclonal antibody against a 180-kDa protein also found in the nucleolus dense fibrillar component (DFC) (24). Benavente et al (24) suggested that in the absence of rRNA gene, the proteins usually found in the DFC region assemble into spherical bodies not containing proteins normally found in the fibrillar center (FC) or granular component (GC).…”

“…PtK 2 cells, the male lineage, have only one NOR-bearing chromosome per cell, and upon micronucleation only the micronuclei containing that chromosome will be able to form a normal nucleolus and produce rRNAs (23). Earlier studies have shown that NOR-devoid PtK 2 micronuclei present nucleolus-related fibrillar bodies or dots (24,25). These bodies were not recognized by anti-RNA polymerase I antibodies but reacted with antiserum against fibrillarin and with a monoclonal antibody against a 180-kDa protein also found in the nucleolus dense fibrillar component (DFC) (24).…”

“…These bodies were not recognized by anti-RNA polymerase I antibodies but reacted with antiserum against fibrillarin and with a monoclonal antibody against a 180-kDa protein also found in the nucleolus dense fibrillar component (DFC) (24). Benavente et al (24) suggested that in the absence of rRNA gene, the proteins usually found in the DFC region assemble into spherical bodies not containing proteins normally found in the fibrillar center (FC) or granular component (GC). In contrast, another study conducted on the female lineage PtK 1 cells employing three different human autoimmune sera specific for FC, DFC, and GC antigens as characterized by electron microscopy and immunoblotting, reported that each of these nucleolar antigens tested could be found in the dots (25).…”