GSE173652
Asymmetrical forward and reverse developmental trajectories determine molecular programs of B cell antigen receptor editing
During B lymphopoiesis, B cell progenitors progress through alternating and mutually exclusive stages of clonal expansion and immunoglobulin (Ig) gene rearrangements. Great diversity is generated through the stochastic recombination of Ig gene segments encoding heavy and light chain variable domains. However, this commonly generates autoreactivity. Receptor editing is the predominant tolerance mechanism for self-reactive B cells in the bone marrow (BM). B cell receptor editing rescues autoreactive B cells from negative selection through renewed light chain recombination first at Ig? then Ig? loci. Receptor editing depends upon BM microenvironment cues and key transcription factors such as Nuclear factor kappa B, Forkhead box protein O and Transcription Factor 3. The specific BM factor required for receptor editing is unknown. Furthermore, how transcription factors coordinate these developmental programs to promote usage of the ?-chain remain poorly defined. Therefore, we utilized two mouse models that recapitulate pathways by which Ig? light chain positive B cells develop. The first possess deleted J kappa (J?) genes and, as such, models Ig? expression resulting from failed Ig? recombination (Ig?del). The second models autoreactivity by ubiquitous expression of a single-chain chimeric anti-Ig? antibody (?-mac). Here, we demonstrated that autoreactive B cells transit asymmetric forward and reverse developmental trajectories. This imparted a unique epigenetic landscape on small pre-B cells, which opened chromatin to transcription factors essential for Ig? recombination. The consequences of this asymmetric developmental path were both amplified and complemented by CXCR4 signaling. These findings reveal how intrinsic molecular programs integrate with extrinsic signals to drive receptor editing. Overall design: 63 samples collectively from Kappa-macroself mice (B6.Cg-Pepcb Ptprca Tg(UBC-scFv)2Nemz/J JAX Stock No: 006259), IgK deleted mice (PMID: 8458340), WT (Littermate control from Kappa-macroself mice), Cxcr4fl/fl Mb1-cre+ Kappa-macroself (+) and Cxcr4fl/fl Mb1-cre+ Kappa-macroself (-) mice. Sorted small pre-B (B220+CD19+CD43-IgM-FSClo) and immature B cells (B220loCD19+CD43-IgM+) were subjected to ATAC-seq (20 samples) and RNA-seq (19 samples). Small pre-B cells (B220+CD19+CD43-IgM-FSClo) were sorted from Cxcr4fl/fl Mb1-cre+ Kappa-macroself (+) and Cxcr4fl/fl Mb1-cre+ Kappa-macroself (-) mice, expanded in culture in the presence or absence of IL-7 and CXCL12 then subjected to RNA-seq (24 samples). Sorted small pre-B (B220+CD19+CD43-IgM-FSClo), large pre-B (B220+CD19+CD43-IgM-FSChi), immature B (B220loCD19+CD43-IgM+) from CD45.1 and CD45.2 mice were subjected to RNA-seq(14 samples).