Figure 1.

Xbp1-dependent gene expression program in plasmablasts. (A) Scatter plot of gene expression differences between Cd23-Cre Xbp1 ^fl/fl and Xbp1 ^fl/fl PBs that were sorted as CD19⁺CD138⁺CD23^–cells after stimulation in the iGB system for 4 days with IL-4 followed by 4 days with IL-21. Two independent RNA-seq experiments were performed with PBs of each genotype. Each dot corresponds to one gene, whose expression is plotted as normalized log₁₀ (norm rlog) expression value. Genes with an expression difference of > 3-fold, an adjusted P value of < 0.05, a transcripts per million (TPM) expression value of > 5 (at least in one sample) are colored in blue or red corresponding to activation or repression by Xbp1, respectively. (B) Functional classification and quantification (number) of proteins encoded by Xbp1-activated and Xbp1-repressed genes. (C) Expression of genes involved in UPR or ER function, shown as mean TPM values of two RNA-seq experiments of Cd23-Cre Xbp1 ^fl/fl or Xbp1 ^fl/fl PBs, respectively. (D) Presence of Xbp1 peaks in distal regions, gene bodies and promoter (TSS) regions. Splenic B cells from Xbp1 ^Bio/Bio Rosa26 ^BirA/+ mice were stimulated for 4 days with LPS followed by Bio-ChIP-seq analysis. The Xbp1 peaks were assigned to genes as described (22). (E) Consensus Xbp1-binding motif identified with an E-value of 1 x 10^-87 by the de novo motif-discovery program MEME-Chip. (F) The number of regulated target genes is shown for the indicated fold-change of gene expression between Cd23-Cre Xbp1 ^fl/fl and Xbp1 ^fl/fl PBs. Grey bars indicated activated or repressed genes with less than a 3-fold expression change. (G) Expression of Xbp1-activated transcription factor genes in Cd23-Cre Xbp1 ^fl/fl and Xbp1 ^fl/fl PBs, shown as mean TPM values of two RNA-seq experiments per genotype. (H) Xbp1 binding and RNA-seq expression at selected activated Xbp1 target loci. Horizontal bars indicate Xbp1s-Bio peaks identified by MACS peak calling.