Long Noncoding RNA as Modular Scaffold of Histone Modification Complexes

A Lot of HOTAIR The roles of several classes of small (<50 nucleotides) noncoding RNAs are beginning to be defined in molecular detail, whereas the function of most of the long (∼200+ nucleotides), intergenic noncoding (linc)RNAs found in most eukaryotic genomes remains something of a mystery. The HOTAIR lincRNA, which is transcribed from the mouse HOXC locus, binds to the Polycomb Repressive Complex 2 (PRC2) and recruits it to HOXD and other genes, where its histone methylase activity acts to repress gene transcription. Tsai et al. (p. 689 , published online 8 July) now show that HOTAIR also binds to a histone demethylase enzyme, LSD1, part of the CoREST/REST repressor complex. LSD1 acts to remove transcription-activating histone marks, reinforcing the repressive activity of the PRC2 complex. HOTAIR thus functions as a platform for the coordinated binding of PRC2 and LSD1-containing complexes to genes, as revealed in a genome-wide analysis of PRC1/CoREST/REST co-regulated genes.