IL-7R signalling activates widespread VH and DH gene usage to drive antibody diversity in bone marrow B cells

Generation of the primary antibody repertoire requires V(D)J recombination of hundreds of gene segments in the immunoglobulin heavy chain (Igh) locus. It has been proposed that interleukin-7 receptor (IL-7R) signalling is necessary for Igh recombination, but this has been challenging to partition from the receptor's role in B cell survival and proliferation. By generating the first detailed description of the Igh repertoire of murine IL-7Ra-/- bone marrow B cells, we demonstrate that IL-7R signalling profoundly influences VH gene selection during VH-to-DJH recombination. We find skewing towards usage of 3' VH genes during de novo VH-to-DJH recombination that is more severe than the fetal liver (FL) B cell repertoire, and we now show a role for IL-7R signalling in DH-to-JH recombination. Transcriptome and accessibility analyses suggests reduced expression of B lineage-specific transcription factors (TFs) and their targets, and loss of DH and VH antisense transcription in IL-7Rα-/- B cells. These results refute models suggesting that IL-7R signalling is only required for survival and proliferation, and demonstrate a pivotal role in shaping the Igh repertoire by activating underpinning epigenetic mechanisms. Examination of WT, FL and IL-7Ra-/- Igh loci in mouse pro-B cells原发性抗体库的生成需要对免疫球蛋白重链（Igh）基因座上的数百个基因片段进行V(D)J重排。此前有研究提出，白细胞介素7受体（IL-7R）信号通路对Igh重排是必需的，但该通路的这一功能很难与其在B细胞存活与增殖中的作用区分开来。本研究首次详细描述了小鼠IL-7Ra基因敲除（IL-7Ra⁻/⁻）骨髓B细胞的Igh库，结果证实IL-7R信号通路在VH-to-DJH重排过程中对VH基因选择具有显著调控作用。我们发现，在新生VH-to-DJH重排过程中，B细胞对3'端VH基因的使用偏好性比胎肝（FL）B细胞库更为显著；同时本研究首次揭示了IL-7R信号通路在DH-to-JH重排过程中的作用。转录组与染色质可及性分析显示，IL-7Ra⁻/⁻ B细胞中B细胞谱系特异性转录因子（TFs）及其靶基因的表达水平下调，且DH和VH反义转录现象完全消失。上述结果驳斥了“IL-7R信号通路仅参与B细胞存活与增殖”的相关模型，并证实该通路通过激活核心表观遗传机制，在塑造Igh抗体库过程中发挥关键调控作用。本研究针对小鼠前B细胞中的野生型（WT）、胎肝（FL）来源及IL-7Ra⁻/⁻的Igh基因座开展了分析。