question: What is the role of the Tsix gene during X chromosome inactivation?
answer: One of the two X chromosomes in female mammalian cells is subject to inactivation (XCI) initiated by the Xist gene. Xist works as a functional RNA molecule that recruits repressive chromatin factors towards one of the female Xs for inactivation. The Tsix gene, antisense of Xist, through transcription negatively regulates Xist and protects one X-chromosome in cis from inactivation by Xist. Although, the precise molecular mechanism is still unclear it has been shown that Tsix transcription regulates the chromatin structure by altering histone tail modifications and DNA methylation at the Xist promoter. In addition, Xist and Tsix RNAs form duplexes in vivo and are processed to small RNAs, which have a potential regulatory function.