paraspeckle

frame|An overlay of a fluorescence micrograph (green) onto a DIC image of a HeLa cell expressing a Yellow fluorescent Protein fusion of Paraspeckle Protein 1 (PSP1): 1. cytoplasm; 2. nucleus; 3. nucleolus; 4. paraspeckles In cell biology, a paraspeckle is an irregularly shaped compartment of the cell, approximately 0.2-1 μm in size, found in the nucleus' interchromatin space. First documented in HeLa cells, where there are generally 10-30 per nucleus, Paraspeckles are now known to also exist in all human primary cells, transformed cell lines and tissue sections. Their name is derived from their distribution in the nucleus; the "para" is short for parallel and the "speckle" refers to the splicing speckles to which they are always near. Their function is still not fully understood, but they are thought to regulate gene expression by sequestrating proteins or mRNAs with inverted repeats in their 3′ UTRs.

== Structure == left|thumb|300x300px|West et al. (2016) suggest that the NEAT1 is folded and bound to paraspeckle core proteins to first form units, which are bridged together by FUS proteins to form the ordered paraspeckle sphere. Paraspeckles are organised into core-shell spheroidal structures; seven proteins on a scaffold of lncRNA NEAT1 (the 23kb isoform termed NEAT1_2 or NEAT1v2). In 2016, West et al. proposed the currently accepted model for Paraspeckles. This was based on their current findings using super-resolution microscopy. Their models state that the NEAT1_2 scaffold folds into a V-shaped unit. Many of these units then are assembled into a core-shell spheroid by FUS proteins. Core proteins SFPQ, NONO and PSPC1 tightly associate to the assembled structure. Finally, the shell forms, composed of partially co-localised TDP43 proteins. Due to the integral nature of NEAT1 to paraspeckles assembly, assembly is thought to occur close to NEAT1 transcription sites.