Deletion of Xist intron 1 and the Tsix promoter causes upregulation of transgenic Xist expression in undifferentiated XY ES cell lines. (A) Graphs showing proportional representation of four patterns of Xist expression in XY ES clones carrying P1 transgenes: light grey, no detectable Xist expression; red, upregulated Xist cloud; grey, two punctate Xist signals; dark grey, one punctate Xist signal. Each bar represents an individual clone. (B) qRT-PCR analysis of Xist expression in XY ES clones carrying P1 transgenes. All data is normalised to β-actin transcript levels and presented relative to the wt XY ES (129/1) Xist RNA level. Each bar represents an individual clone. ES: embryonic stem; qRT-PCR: quantitative reverse transcription polymerase chain reaction; wt: wild type.