Project description:Analysis of the gene expression profile between MYC positive and MYC negative germinal center B-cells. Total RNA isolated from MYC positive and MYC negative GC B-cells, isolated by FACS from 10 day sheep red blood cell immunized mice MycEGFP (a Myc reporter allele, in which a MYC-EGFP fusion protein (MYCEGFP) is expressed from the endogenous Myc locus, Huan, CY et al Eur J Immunol 2008)
Project description:Characterisation of the splenic light zone germinal center B cells in mice carrying WT endogenous mouse allele and mice carrying a mouse allele (Myc V394D) unable to bind its partner transcription factor Miz1 (Zbtb17). Characterisation of Myc WT memory B cells.
Project description:Splenic germinal center B cells (B220pos, CD19pos, CD38 low, FAS high) were isolated from animals 10 days sheep red blood cell immunised animals using flow cytometry cell sorter. Animals carry a combination of alleles that allows germinal center B cell deletion of endogenous Myc allele and simultaneous conditional overexpression of human MYC in its wild-type for or mutant form in which a valine in residue 394 has been substituted by an aspartic acid.
Project description:We used RNA sequencing to characterize gene expression of Ly75+/+ B1-8hi and Ly75-/- B1-8hi B cells from the germinal center light zone (LZ) 12 h after forcing positive selection of the Ly75+/+ population with anti-DEC205-OVA.
Project description:Productive B cell responses are critical to protect a host from infection. The spleen and lymph nodes are populated by resting follicular B cells, which can enter germinal centers upon antigen encounter. Once in the germinal center, B cells migrate between the dark and light zones, where they undergo somatic hypermutation and selection, respectively. While germinal center B cells have been studied, an intense molecular understanding of these cells/subsets (and the differences between them) is lacking.
Project description:Germinal centers (GC) arise within B cell follicles upon antigenic challenge. In the dark zones (DZ) of GCs, B cells proliferate and hypermutate their immunoglobulin genes, and mutants with increased affinity are positively selected in the light zone (LZ) to either differentiate into plasma and memory cells, or re-enter the DZ for further refinement. However, the molecular circuits governing GC positive selection are not known. Here, we show that the GC reaction requires the biphasic regulation of c-MYC expression, involving its transient induction during early GC commitment, its repression by BCL6 in DZ B cells, and its re-induction in a subpopulation of positively selected LZ B cells destined to DZ re-entry. Accordingly, acute disruption of MYC function in vivo leads to GC collapse, indicating an essential role in GC physiology. These results have implications for our understanding of GC selection and the role of MYC deregulation in B cell lymphomas. We used microarrays to determine the global gene expression programs that distinguish MYC+ GC B cells from their MYC- negative counterparts.
Project description:Germinal centers (GC) arise within B cell follicles upon antigenic challenge. In the dark zones (DZ) of GCs, B cells proliferate and hypermutate their immunoglobulin genes, and mutants with increased affinity are positively selected in the light zone (LZ) to either differentiate into plasma and memory cells, or re-enter the DZ for further refinement. However, the molecular circuits governing GC positive selection are not known. Here, we show that the GC reaction requires the biphasic regulation of c-MYC expression, involving its transient induction during early GC commitment, its repression by BCL6 in DZ B cells, and its re-induction in a subpopulation of positively selected LZ B cells destined to DZ re-entry. Accordingly, acute disruption of MYC function in vivo leads to GC collapse, indicating an essential role in GC physiology. These results have implications for our understanding of GC selection and the role of MYC deregulation in B cell lymphomas. We used microarrays to determine the global gene expression programs that distinguish MYC+ GC B cells from their MYC- negative counterparts. GFPMYC+ and GFPMYC- GC B cell subpopulations were collected by Fluorescence Activated Cell Sorting (FACS) from B cell enriched fractions of splenic mononuclear cell pools of GFPMYC knock-in mice (12 days after SRBC immunization). 5-20ng of total RNA (RIN>9) for each sample was used as a template for linear cDNA amplification (Ovation RNA amplification Kit, NuGen). cDNA was labeled using the Encore Biotin Labeling Kit (NuGen) and hybridized to Affymetrix Mouse 430.2 gene expression arrays.
Project description:High affinity B cell selection in the germinal center (GC) is governed by signals delivered by follicular helper T cells (Tfh) to B cells. Selected B cells undergo clonal expansion and affinity maturation in the GC dark zone in direct proportion to the amount of antigen they capture and present to Tfh cells in the light zone. Here we examined the mechanisms whereby Tfh cells program the number of GC B cell divisions. Gene expression analysis revealed that Tfh induce MYC expression in light zone B cells in direct proportion to antigen capture. Conditional Myc haplo-insufficiency or over-expression combined with cell division tracking showed that MYC expression produces a metabolic reservoir in selected light zone B cells that is proportional to the number of cell divisions in the dark zone. Thus, MYC constitutes the germinal center B cell division timer that when deregulated leads to emergence of B cell lymphoma.
Project description:High expression of MYC and its target genes define a subset of germinal center B-cell diffuse large B-cell lymphoma (GCB-DLBCL) associated with poor outcomes. Half of these high-grade cases show chromosomal rearrangements between the MYC locus and heterologous enhancer-bearing loci, while focal deletions of the adjacent non-coding gene PVT1 are enriched in MYC-intact cases. To identify genomic drivers of MYC activation, we used high-throughput CRISPR-interference (CRISPRi) profiling of candidate enhancers in the MYC locus and rearrangement partner loci in GCB-DLBCL cell lines and mantle cell lymphoma (MCL) comparators that lacked common rearrangements between MYC and immunoglobulin (Ig) loci. Rearrangements between MYC and non-Ig loci were associated with unique dependencies on specific enhancer subunits within those partner loci. Notably, fitness dependency on enhancer modules within the BCL6 super-enhancer (BCL6-SE) cluster regulated by a transcription factor complex of MEF2B, POU2F2, and POU2AF1 was higher in cell lines bearing a recurrent MYC::BCL6-SE rearrangement. In contrast, GCB-DLBCL cell lines without MYC rearrangement were highly dependent on a previously uncharacterized 3’ enhancer within the MYC locus itself (GCBME-1), that is regulated in part by the same triad of factors. GCBME-1 is evolutionarily conserved and active in normal germinal center B cells in humans and mice, suggesting a key role in normal germinal center B cell biology. Finally, we show that the PVT1 promoter limits MYC activation by either native or heterologous enhancers and demonstrate that this limitation is bypassed by 3’ rearrangements that remove PVT1 from its position in cis with the rearranged MYC gene.