Impact of Mek1 and Mek2 deletion on the transcriptome of spleen B cell subpopulations

MEK1 and MEK2, the only known activators of ERK, are attractive therapeutic candidates for autoimmune diseases. The deletion of Mek1 in mouse hematopoietic cells was performed using the Mek1 conditional allele (Map2k1tm1Chrn) and the Vav1-icre deleter mouse line (Commd10Tg(Vav1-icre)A2Kio) in the Mek2 heterozygous null background (Map2k2tm1Chrn). Mek1flox/flox Mek2+/- Tg+/Vav1-icre mice (named thereafter 1Mek2) die prematurely of lymphoproliferative disorders associated with spontaneous B cell activation and the accumulation of plasma cells, age-associated B cells and germinal center B cells (Houde, N., et al. (2022). Cell Rep 38(2): 110223). However, how MEK signaling finely regulates immune cell activation is only partially understood. To address this question, we applied bulk RNA-seq assays to characterize the transcriptional impact of the specific loss of MEK protein in B cell subpopulations using the 1Mek2 mutants. Overall design: To investigate the global transcriptional impact resulting from the loss of Mek1 and Mek2 gene function in B cells, we applied bulk RNA sequencing (RNA-seq) on splenic B cell subpopulations. We extracted splenocytes from 3 to 5 months wild-type and Mek1flox/flox Mek2+/- Tg+/Vav1-icre mice (Houde, N., et al. (2022). Cell Rep 38(2): 110223.). Following splenocyte isolation, B cell subpopulations were purified by cell sorting: plasma cell (P; B220+CD138+), immature (Immature; B220+CD93+CD138-), germinal center (GC; B220+CD93-CD138-GL7+FAS+), follicular (F; B220+CD93-CD138-GL7-FAS-CD21+CD23+), marginal zone B cell (M; B220+CD93-CD138-GL7-FAS-CD21+CD23-).