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A lncRNA for the active X

Nature Structural & Molecular Biology volume 20, page 308 (2013) | Download Citation

Long noncoding RNAs (lncRNAs) can modulate gene expression in various ways, including by gene silencing. In fact, one of the best-characterized lncRNAs is XIST, a lncRNA with a central role in X-chromosome inactivation in placental mammals. XIST is transcribed from and coats the inactive X chromosome, and, together with other lncRNAs, it promotes the recruitment of histone-modifying complexes to initiate and maintain X-chromosome silencing. Now Rougelle and colleagues have identified a new lncRNA, called XACT (for X-active coating transcript), that coats the active X chromosome. XACT is expressed from the active X chromosome in human embryonic stem cells but undergoes silencing upon differentiation, and its expression could not be detected in fibroblasts or in a number of examined tissues. In cells where XIST expression is lost, XACT is expressed from both X chromosomes. XACT does not seem to be conserved in mice, as indicated by RNA FISH analyses of mouse embryonic stem cells. The authors propose that XACT is involved in controlling the initiation of X-chromosome inactivation in the human embryo, a process that occurs with different kinetics compared to those of the mouse embryo. Future work will elucidate the precise role of XACT, but its identification as a lncRNA that coats active chromatin expands the already diverse functions that lncRNAs can exert in regulating gene expression. (Nat. Genet. doi:10.1038/ng.2530, published online 20 January 2013)

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https://doi.org/10.1038/nsmb.2538

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