Tsix is maternally expressed in the blastocyst and in extraembyronic tissues. Tsix is expressed on
the future active X and may be the factor which protects the maternal X from inactivation by Xist
in extra-embryonic tissues (Lee
JT, 2000; Lee
JT et al, 1999; Sado
T et al, 2001).
However, since Tsix expression is detected only in a minority of cells before the blastocyst stage,
it is unlikely to propagate the maternal imprint in the preimplantation embryo (Ideraabdullah
FY et al, 2008).
Tsix is dispensable for inhibiting Xist and X-inactivation in the early embryo and is instead
required to prevent Xist expression as trophectodermal progenitor cells differentiate (Maclay E et al, 2014).