The long noncoding RNA is seemingly dispensable for normal tissue homeostasis and cancer cell growth.

is one of the most studied lncRNAs, in part because its silencing in mice causes defects in mammary gland development and corpus luteum formation and protects them from skin cancer development. Moreover, depleting in established cancer cell lines reduces growth and sensitizes cells to DNA damaging agents. However, produces two isoforms and because the short isoform, , completely overlaps the 5' part of the long isoform; the respective contributions of each of the isoforms to these phenotypes has remained unclear. Whereas is highly expressed in most tissues, is the central architectural component of paraspeckles, which are nuclear bodies that assemble in specific tissues and cells exposed to various forms of stress. Using dual RNA-FISH to detect both outside of the paraspeckles and inside this nuclear body, we report herein that levels are dynamically regulated during the cell cycle and targeted for degradation by the nuclear RNA exosome. Unexpectedly, however, cancer cells engineered to lack , but not , do not exhibit cell cycle defects. Moreover, -specific knockout mice do not exhibit the phenotypes observed in -deficient mice. We propose that functions are mainly, if not exclusively, attributable to and, by extension, to paraspeckles.