Transcriptomic analysis of in-vitro plasma cell generation from follicular B cells lacking Xbp1 [Xbp1_PC_stim]

During plasma cell differentiation there is activation of UPR gene expression that has been termed the physiological UPR of plasma cell differentiation. This is canonically thought to be downstream of Blimp1-mediated increases in immunoglobulin gene production and activation of the Xbp1 transcription factor by the RNA splicing activity of the ER-stress sensor IRE1a. Having observed UPR-affiliated gene expression prior to upregulation of Blimp1 as reported in the companion linked series, we endeavored to determine the necessity of Xbp1 activity in the early remodeling of the ER in nascent plasma cells. To this end, we mated mice harboring a floxed exon 2 of the Xbp1 gene (Xbp1flox) to mice expressing a tamoxifen-inducible cre recombinase under the control of the human CD20 promoter (hCD20-TamCre). These mice and their hCD20-TamCre-Xbp1wt litermates were fed oral tamoxifen in their diet for two weeks and follicular B cells were prepared for in-vitro plasma cell differentiation studies. We report here that prior to plasma cell differentiation as measured by CD138 expression, which coincides temporally with Blimp1 expression, there is no defect in UPR-affiliated gene expression in cells lacking Xbp1. Overall design: Samples are follicular B cells from Xbp1-floxed (n=5) and Xbp1-wildtype (n=3) mice expressing tamoxifen inducible Cre under the CD20 promoter after tamoxinen treatment, stimulated in culture to produce plasma cells. cDNA was prepared from RNA with 3' polyA capture method. Transcript abundance was measured by Kallisto psuedo-alignment and normalized (voom) and differential expression was assessed using limma.