NEAT1 RNA, a highly abundant 4 kb ncRNA, is retained in nuclei in approximately 10 to 20 large foci that we show are completely coincident with paraspeckles, nuclear domains implicated in mRNA nuclear retention. Depletion of NEAT1 RNA via RNAi eradicates paraspeckles, suggesting that it controls sequestration of the paraspeckle proteins PSP1 and p54, factors linked to A-I editing. Unlike overexpression of PSP1, NEAT1 overexpression increases paraspeckle number, and paraspeckles emanate exclusively from the NEAT1 transcription site. The PSP-1 RNA binding domain is required for its colocalization with NEAT1 RNA in paraspeckles, and biochemical analyses support that NEAT1 RNA binds with paraspeckle proteins. Unlike other nuclear-retained RNAs, NEAT1 RNA is not A-I edited, consistent with a structural role in paraspeckles. Collectively, results demonstrate that NEAT1 functions as an essential structural determinant of paraspeckles, providing a precedent for a ncRNA as the foundation of a nuclear domain. © 2009 Elsevier Inc. All rights reserved.
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