Project description:During B cell development the precursor B cell receptor (pre-BCR) checkpoint is thought to increase immunoglobulin k light chain (Igk) locus accessibility to the V(D)J recombinase. Accordingly, pre-B cells lacking the pre-BCR signaling molecules Btk or Slp65 showed reduced germline Vk transcription. To investigate whether pre-BCR signaling modulates Vk accessibility through enhancer-mediated Igk locus topology, we performed chromosome conformation capture and sequencing analyses. These revealed that already in pro-B cells the k enhancers robustly interact with the ~3.2 Mb Vk region and its flanking sequences. Analyses in wild-type, Btk and Slp65 single and double-deficient pre-B cells demonstrated that pre-BCR signaling reduces interactions of both enhancers with Igk locus flanking sequences and increases interactions of the 3â??k enhancer with Vk genes. Remarkably, pre-BCR signaling does not significantly affect interactions between the intronic enhancer and Vk genes, which are already robust in pro-B cells. Both enhancers interact most frequently with highly used Vk genes, which are often marked by transcription factor E2a. We conclude that the k enhancers interact with the Vk region already in pro-B cells and that pre-BCR signaling induces accessibility through a functional redistribution of long-range chromatin interactions within the Vk region, whereby the two enhancers play distinct roles. We performed genome-wide expression profiling of FACS-purified B220+CD19+ pre-B cell fractions from wild-type (WT), Btk and Slp65 single and double deficient VH81x transgenic Rag1-/- mice (n=4 of each genotype). In these experiments non-VH81x transgenic Rag1-/- pro-B cells served as controls (n=3).
Project description:During B cell development the precursor B cell receptor (pre-BCR) checkpoint is thought to increase immunoglobulin k light chain (Igk) locus accessibility to the V(D)J recombinase. Accordingly, pre-B cells lacking the pre-BCR signaling molecules Btk or Slp65 showed reduced germline Vk transcription. To investigate whether pre-BCR signaling modulates Vk accessibility through enhancer-mediated Igk locus topology, we performed chromosome conformation capture and sequencing analyses. These revealed that already in pro-B cells the k enhancers robustly interact with the ~3.2 Mb Vk region and its flanking sequences. Analyses in wild-type, Btk and Slp65 single and double-deficient pre-B cells demonstrated that pre-BCR signaling reduces interactions of both enhancers with Igk locus flanking sequences and increases interactions of the 3’k enhancer with Vk genes. Remarkably, pre-BCR signaling does not significantly affect interactions between the intronic enhancer and Vk genes, which are already robust in pro-B cells. Both enhancers interact most frequently with highly used Vk genes, which are often marked by transcription factor E2a. We conclude that the k enhancers interact with the Vk region already in pro-B cells and that pre-BCR signaling induces accessibility through a functional redistribution of long-range chromatin interactions within the Vk region, whereby the two enhancers play distinct roles.
Project description:B lymphopoiesis requires that immunoglobulin genes be accessible to RAG1-RAG2 recombinase. However, the RAG proteins bind widely to open chromatin, which suggests that additional mechanisms must restrict RAG-mediated DNA cleavage. Here we show that developmental downregulation of interleukin 7 (IL-7)-receptor signaling in small pre-B cells induced expression of the bromodomain-family member BRWD1, which was recruited to a specific epigenetic landscape at Igk dictated by pre–BCR-dependent Erk activation. BRWD1 enhanced RAG recruitment, increased gene accessibility and positioned nucleosomes 5? to each J? recombination signal sequence. BRWD1 thus targets recombination to Igk and places recombination within the context of signaling cascades that control B cell development. Our findings represent a paradigm in which,at any particular antigen-receptor locus, specialized mechanisms enforce lineage- and stage-specific recombination. ChIP-seq for 1 transcription factor and 2 histone modifications in flow purified mouse small pre-B cells. ATAC-seq and RNA-seq in WT and Brwd-Mut mouse flow purified small pre-B cells.
Project description:B lymphopoiesis requires that immunoglobulin genes be accessible to RAG1-RAG2 recombinase. However, the RAG proteins bind widely to open chromatin, which suggests that additional mechanisms must restrict RAG-mediated DNA cleavage. Here we show that developmental downregulation of interleukin 7 (IL-7)-receptor signaling in small pre-B cells induced expression of the bromodomain-family member BRWD1, which was recruited to a specific epigenetic landscape at Igk dictated by pre–BCR-dependent Erk activation. BRWD1 enhanced RAG recruitment, increased gene accessibility and positioned nucleosomes 5′ to each Jκ recombination signal sequence. BRWD1 thus targets recombination to Igk and places recombination within the context of signaling cascades that control B cell development. Our findings represent a paradigm in which,at any particular antigen-receptor locus, specialized mechanisms enforce lineage- and stage-specific recombination.
Project description:In B lymphopoiesis, activation of the pre-B cell antigen receptor (pre-BCR) is associated with both cell cycle exit and Igk recombination. Yet, how the pre-BCR mediates these functions remains unclear. Herein, we demonstrate that the pre-BCR initiates a feed-forward IRF4-CXC Receptor 4 (CXCR4) amplification loop. ERK activation by CXCR4 then directs the development of small and immature B cells including orchestrating cell cycle exit, pre-BCR repression, Igk recombination and BCR expression. In contrast, escape from IL-7 and pre-BCR expression have only modest effects on B cell developmental transcriptional and epigenetic programs. These data demonstrate a direct and central role for CXCR4 in orchestrating late B cell lymphopoiesis. Furthermore, in the context of previous findings, our data provide a three-receptor system sufficient to recapitulate the essential features of B lymphopoiesis in vitro.
Project description:We report that in developing B cells individual enhancers of Igk make up super-enhancer cluster where contacts between its components rely on all constituents. Reduction of interaction frequency in enhancer knock-out cells is associated with deminished transcriptional output of enhancers and Igk locus. Moreover, we find that Igk enhancer MiEk has an effect on levels of CBFb enrichment on Tcrb enhancer, Eb afffecting Tcrb recombination and T cell development.
Project description:We report that in developing B cells individual enhancers of Igk make up super-enhancer cluster where contacts between its components rely on all constituents. Reduction of interaction frequency in enhancer knock-out cells is associated with deminished transcriptional output of enhancers and Igk locus. Moreover, we find that Igk enhancer MiEk has an effect on levels of CBFb enrichment on Tcrb enhancer, Eb afffecting Tcrb recombination and T cell development.
Project description:We report that in developing B cells individual enhancers of Igk make up super-enhancer cluster where contacts between its components rely on all constituents. Reduction of interaction frequency in enhancer knock-out cells is associated with deminished transcriptional output of enhancers and Igk locus. Moreover, we find that Igk enhancer MiEk has an effect on levels of CBFb enrichment on Tcrb enhancer, Eb afffecting Tcrb recombination and T cell development.