Single-cell chromatin accessibility of MBCs, prePBs, plasmablasts, and PCs during B to PC differentiation. (A) UMAP representation of the 4 stages analyzed separately and then merged together. Peaks detected with MACS2 peak calling were used for UMAP representation. (B) Number of differentially accessible peaks identified for the 4 stages using pairwise comparisons (one stage vs all other cells). (C) Cells were fixed with 4% paraformaldehyde for 10 minutes at different time points: MBCs (day 0), PrePBs (day 4), PBs (day 7), and PCs (day 10). Immunofluorescence to detect H3K27me3 levels (green) was performed with an anti-H3K27me3 antibody. DNA was stained with DAPI (4′,6-diamidino-2-phenylindole) (red). Scale bar, 10 μm. (D) Proportion of peaks localized on genes (in blue) and distal elements (in green) for each stage. (E-G) Volcano plots of differentially accessible peaks identified during transitions: from MBC to prePB, from prePB to PB, and from PB to PC, respectively. Peaks identified as significantly accessible were colored in blue (P value <.05 and log2(fold change) > 0.25). (H) Venn diagrams representing genes that were upregulated in RNA-seq data set (in blue) and/or associated with more open chromatin in ATAC-seq data set (in green). (I) Peak tracks of BATF and BATF3 revealing differentially accessible peaks on BATF and BATF3 genes and on distal elements. (J) TF motif enrichment of differentially accessible peaks for each stage. (K) mRNA expression of TFs belonging to the AP-1 family in the 4 stages using the RNA-seq data set. (L) Proportion of differentially accessible peaks in the prePB stage enriched in BATF3 motif. (M) Venn diagram of the number of genes upregulated in the prePB stage identified using the RNA-seq data set and the number of genes associated with a more open chromatin enriched in BATF3 motif identified using ATAC-seq data set. Common genes represented potential BATF3 targets.