Dynamics of Polycomb chromatin domains under conditions of increased molecular crowding.
BACKGROUND
A Polycomb (PcG) body is an orphan nuclear subcompartment characterised by accumulations of Polycomb repressive complex 1 (PRC1) proteins. However, seemingly contradictory reports have appeared that describe the PcG bodies either as protein-based bodies in the interchromatin compartment or chromatin domains. In this respect, molecular crowding is an important factor for the assembly and stability of nuclear subcompartments. In order to settle this contradiction, crowding experiments, that represent a convenient model distinguishing between interchromatin and chromatin compartments, were carried out.


RESULTS
In sucrose-hypertonically induced crowding, we observed in U-2 OS cells that PcG bodies disappeared, but persisted as nuclear domains characterised by accumulations of DNA. This phenomenon was also observed in cells hypertonically treated with sorbitol and NaCl. Importantly, the observed changes were quickly reversible after re-incubation of cells in normal medium. We found that the PcG foci disappearance and the dissociation of PRC1 proteins (BMI1 and RING1a proteins) from chromatin were associated with their hyper-phosphorylation. In addition, under hyper- and hypotonic conditions, the behaviour of the PcG bodies differed from that of the typical nucleoplasmic body.


CONCLUSIONS
PRC1 proteins accumulations do not represent a genuine nuclear subcompartment. The PcG body is a chromosomal domain, rather than a nucleoplasmic body.
Charles University in Prague, First Faculty of Medicine, Institute of Cellular Biology and Pathology, Czech Republic.
Jana
J
Šmigová
Pavel
P
Juda
Eva
E
Bártová
Ivan
I
Raška
D000880:Anthraquinones / Q000378:metabolism; D045744:Cell Line, Tumor; D002843:Chromatin / Q000378:metabolism*; D005453:Fluorescence; D006801:Humans; D006982:Hypertonic Solutions / Q000494:pharmacology; D046911:Macromolecular Substances / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D063150:Polycomb Repressive Complex 1 / Q000378:metabolism; D063146:Polycomb-Group Proteins / Q000378:metabolism*; D012313:RNA / Q000235:genetics / Q000378:metabolism; D013194:Staining and Labeling; D013395:Sucrose / Q000494:pharmacology; D014158:Transcription, Genetic / Q000187:drug effects
C520537:1,5-bis((2-(methylamino)ethyl)amino)-4,8-dihydroxyanthracene-9,10-dione; D000880:Anthraquinones; C069077:BMI1 protein, human; D002843:Chromatin; D006982:Hypertonic Solutions; D046911:Macromolecular Substances; D063146:Polycomb-Group Proteins; D013395:Sucrose; D012313:RNA; D063150:Polycomb Repressive Complex 1; C080355:RING1 protein, human
Molecular crowding; Nuclear subcompartments; Polycomb body; Polycomb group proteins; Post-translational chromatin modifications