High impact information on TSIX

• Tsix, a gene antisense to Xist at the X-inactivation centre [1].
• Before the onset of X inactivation, Tsix is expressed from both X chromosomes [1].
• Yy1 and Ctcf associate through specific protein-protein interactions and together transactivate Tsix [2].
• Following choice, the asymmetry of Xite and Tsix expression drives divergent chromosome fates, but how this pattern becomes established is currently unknown [2].
• Now, using RNA FISH for cellular localization of transcripts in human fetal cells, we show that human TSIX antisense transcripts are unable to repress XIST [3].

Biological context of TSIX

• These differences could explain the fact that X inactivation is not imprinted in human placenta, and they raise questions about the role of TSIX in random X inactivation [4].
• Human TSIX produces a >30-kb transcript that is expressed only in cells of fetal origin; it is expressed from human XIC transgenes in mouse embryonic stem cells and from human embryoid-body-derived cells, but not from human adult somatic cells [4].
• In fact, TSIX is transcribed only from the inactive X chromosome and is coexpressed with XIST [3].
• Also, TSIX is not maternally imprinted in placental tissues, and its transcription persists in placental and fetal tissues, throughout embryogenesis [3].
• In XCI, TSIX serves as an antisense regulator of XIST, the silencer element for XCI which itself makes a non-coding transcript [5].

Anatomical context of TSIX

• In the present study we show that both Xist RNA and Tsix RNA, an antisense RNA that controls Xist function in the soma, are expressed in the testis in a germ-cell-dependent manner [6].

References