Med1 deficiency affects IgH chromatin dynamics during CSR. (A and B) High-resolution 4C-Seq was performed using a bait on the Eμ enhancer (red dot). A schematic map of the IgH locus indicates the I exons (black dots), S regions (gray boxes), the constant region exons (white boxes), the Eμ enhancer, the γ1 enhancer (γ1E), and the DNaseI hypersensitive sites (hs) located in the 3′ RR. Curved lines indicate long-range interactions. 4C-Seq signal was calculated using 10-kb windows centered on DpnII sites located in the constant region of IgH (chr12: 113175000–113475000, mm10). Full lines represent the mean of three replicates and dashed lines the signal for each replicate. The 4C-Seq analysis was conducted with three biological replicates per time point (day 0 and day 2), genotype (Med1^F/F and Med1^F/FMb1^Cre/+), and stimulation: resting B cells and LPS + IL-4–stimulated cells (A) and resting B cells and LPS-stimulated cells (B). We focused our analysis on the RRs and on the regions whose transcription is specifically induced upon stimulation with LPS or LPS + IL-4 (black bars). In this focused analysis, a Welch’s t test (two-sample and two-sided) was used on the mean score for all windows centered within the chosen regions to assess significant differences, taking into account the three replicates for each sample. P-values are indicated. The γ2bp-Sγ2b region is indicated with an arrow.