X-Chromosome Inactivation and Long Non-Coding RNAs

The X-linked region known as the 'X-inactivation center' (Xic) was once dominated by protein-coding genes but, with the rise of Eutherian mammals some 150-200 million years ago, became infiltrated by genes that produce long noncoding RNA (lncRNA).  Some of the noncoding genes have been shown to play crucial roles during X-chromosome inactivation (XCI), including the targeting of chromatin modifiers to the X. The rapid establishment of lncRNA hints at a possible preference for long transcripts in some aspects of epigenetic regulation.  We will consider advantages lncRNA offers in delivering allelic, cis-limited, and locus-specific control.  Examples include Xist, Tsix, and Jpx.  The mechanisms by which they repress and activate gene expression will be discussed.