ATAC-seq reveals a progressive commitment to alternative cell fates. (A) An Integrated Genomics Viewer (IGV) window, showing RNA-seq and ATAC-seq signals close to the PRDM1 locus in the different cell populations. Red boxes indicate ATAC-seq regions whose densities are correlated with PRDM1 RNA-seq expression. RNA-seq and ATAC-seq tracks are shown on the same scale to facilitate comparisons of the cell populations. Several features extracted from previously published research are also shown. The orange box on the left shows a region that closes with differentiation and in which a BCL6 TFBS was previously described,³⁹  in agreement with the negative regulation of PRDM1 expression by BCL6. (B) A boxplot of ATAC-seq read densities in regions associated with the 200 genes with the highest score (top, 365 regions) or lowest score (bottom, 389 regions) on the RNA-seq rPC1 axis in the NBC, D4lo, P2/CD23⁺, P2/CD23^–, and P1 populations. Note that densities increase with differentiation status for regions associated with PC differentiation genes (PC1 up) but decrease for NBC identity genes (PC1 down). (C) A heatmap of the 2658 DO ATAC-seq regions showing 6 clusters, each of which was specific for 1 or more cell populations. The numbers of regions per cluster are C1, 271; C2, 343; C3, 320; C4, 349; C5, 301; C6, 1074. (D) HOMER analysis of binding sites enriched in the different ATAC-seq DO clusters for selected TFs known to be involved in terminal B-cell differentiation or appearing in the top 10 TFs in 1 of the clusters (see supplemental Figure 2E). (E) Analysis using enrichr of genes associated with DO region clusters, showing an increasing enrichment of genes strongly expressed in PCs. Red bars indicate the significance threshold in hypergeometric or binomial tests (P < .05).