The building process of the functional paraspeckle with long non-coding RNAs

Nuclei of mammalian cells are highly organized and composed of distinct subnuclear structures termed nuclear bodies. Paraspeckles are subnuclear structures that form around the long non-coding RNA (lncRNA) nuclear paraspeckle assembly transcript 1 (NEAT1) together with numerous RNA-binding proteins, many of which contain an RNA-binding domain and a prion-like domain and are related to specific neurodegenerative diseases. Paraspeckle formation proceeds in conjunction with NEAT1 lncRNA biogenesis and involves the cooperation of multiple paraspeckle-localized RNA-binding proteins. NEAT1 lncRNA likely sequesters these RNA-binding proteins in paraspeckle structures, which act as molecular sponges at which the nucleoplasmic activities of the sequestered proteins are modulated. This review presents, firstly, current knowledge regarding factors involved in the formation and function of paraspeckles. Secondly, the intracellular functions of all identified paraspeckle proteins, which are potentially controlled through their sequestration in paraspeckles, are categorized. Thirdly, recently identified nuclear bodies containing putative architectural lncRNAs are described and similarities among the architectures of lncRNA-dependent nuclear bodies are discussed.