The transcriptional imbalance due to the difference in the number of X chromosomes between male and female mammals is remedied through X-chromosome inactivation, the epigenetic transcriptional silencing of one of the two X chromosomes in females.

Scientists discover in the journal Nature Communications that an Xist antisense long non-coding RNA, XistAR (Xist Activating RNA), which is encoded within exon 1 of the mouse Xist gene and is transcribed only from the inactive X chromosome.

Selective truncation of XistAR, while sparing the overlapping Xist RNA, leads to a deficiency in Xist RNA expression in cis during the initiation of X inactivation.

Thus, the Xist gene carries within its coding sequence an antisense RNA that drives Xist expression.

http://www.nature.com/ncomms/2015/151019/ncomms9564/full/ncomms9564.html