Fig. 6.

Rlim-independent activation of Xist in the embryonic epiblast. (A) RNA FISH on sections of representative Rlim KO/KO female embryos in decidua at stages E7.5 using a Xist probe. Representative images depicting epiblast and bordering trophoblast embryonic regions. Green and white arrows indicate trophoblast and epiblast regions, respectively. Note the presence of Xist paints in epiblast cells but very little trophoblasts. (Scale bars: 20 µm.) (B) Model of how the Rlim–Rex1 axis regulates iXCI in female mice. Rlim activity keeps Rex1 below threshold levels required for activation of Xist. Note that it is the dose of Rex1 that is critical for activation of Xist, whether Rlim is present or not.