The enigmatic nuclear structures known as paraspeckles may only be necessary during times of stress, Nakagawa et al. report.

Discovered in 2002, paraspeckles stick close to the larger and better-known splicing speckles that help edit mRNA. Paraspeckles harbor RNA and protein, but researchers aren't sure what they do.

To help pin down their function, Nakagawa et al. analyzed gene expression in different mouse tissues. The noncoding RNA NEAT1_2, a component of paraspeckles, was abundant only in a few cell types, such as the epithelial cells in the linings of the stomach and colon. By contrast, paraspeckles show up in almost all kinds of cultured cells.

The researchers eliminated paraspeckles from mice by deleting the NEAT1 gene. The animals were apparently healthy, suggesting that the loss of paraspeckles was no handicap, at least for life in cushy laboratory conditions. However, paraspeckles may help cells cope with stress. One pressure that could induce formation, the researchers suggest, is infection—previous studies have found that pathogens such as the rabies virus activate the NEAT1 gene. Nakagawa et al. say that future work should determine whether NEAT1-lacking animals can fend off infections and whether abnormalities appear in specific tissues or as the mice age.

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J. Cell Biol.