The nucleolus is a plurifunctional organelle in which structure and function are intimately linked. Its structural plasticity has long been appreciated, particularly in response to transcriptional inhibition and other cellular stresses, though the mechanism and physiological relevance of these phenomena remain unclear. Using MCF-7 and other mammalian cell lines, researchers at the University of Ottawa, Canada describe a structural and functional adaptation of the nucleolus, triggered by heat shock or physiological acidosis, that is dependent upon the expression of ribosomal intergenic spacer long noncoding RNA (IGS lncRNA). At the heart of this process is the de novo formation of a large subnucleolar structure, termed the Detention Center (DC). The DC is a spatially and dynamically distinct region, characterized by an 8-anilino-1-naphthalenesulfonate (ANS)-positive hydrophobic signature. Its formation is accompanied by a redistribution of nucleolar factors and an arrest in ribosomal biogenesis. Silencing of regulatory IGS lncRNA prevents the creation of this structure and allows the nucleolus to retain its tripartite organization and transcriptional activity. Signal termination causes a decrease in IGS transcript levels and a return to the active nucleolar conformation. The researchers propose that the induction of IGS lncRNA, by environmental signals, operates as a molecular switch that regulates the structure and function of the nucleolus.
- Jacob MD, Audas TE, Uniacke J, Trinkle-Mulcahy L, Lee S. (2013) Environmental Cues Induce a Long Noncoding RNA-dependent Remodeling of the Nucleolus. Mol Biol Cell [Epub ahead of print]. [abstract]