Distribution of H3K27 tri-methylation within a 300-kb region of the Xic in undifferentiated male and female embryonic stem (ES) cells. (A) Schematic diagram of the 300-kb region analyzed in our ChIP experiments showing the location of the different transcription units of the Xic. Arrows indicate the direction of each transcription unit. Coding genes are indicated in black, non-coding genes with coloured arrows. The orange box represents the Xite locus, an enhancer region that displays transcriptional activity on the major Tsix promoter. The purple box represents the so-called region B, a complex transcriptional unit that produces both sense and antisense transcripts . We used in each ChIP experiment a set of 383 primer pairs that were designed automatically to cover the 300-kb region (except repeat regions: see Materials and methods). (B) ChIP analysis of H3K27 trimethylation in undifferentiated female (LF2) ES cells and (C) in male (CK35 cell line) ES cells. Both graphs show the percentage of immunoprecipitation (%IP) obtained after normalization to the input. All values are mean ± standard deviation. The average percentage of immunoprecipitation calculated for each position was plotted against the genomic location (bp). The +1 coordinate corresponds to position 1,005,322,247 in NCBI build 37.