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Gene expression analysis of B-NHL from λMYC, λMYC/IµHABCL6, λMYC/AIDKO and λMYC/IµHABCL6/AIDKO mouse models

ABSTRACT: Most human B cell lymphomas (B-NHL) are derived from germinal centers (GCs), the structure where B-cells undergo class switch recombination (CSR) and somatic hypermutation (SHM) and are selected for high-affinity antibody production. The pathogenesis of B-NHL is associated with distinct genetic lesions, including chromosomal translocations and aberrant somatic hypermutation, which appear to arise from mistakes occurring during CSR and SHM. To ascertain the role of CSR and SHM in lymphomagenesis, we crossed three oncogene-driven (MYC, BCL6, MYC/BCL6) mouse models of B cell lymphoma with mice lacking activation-induced cytidine deaminase (AID), the enzyme required for both processes. We show that AID deficiency prevents BCL6-dependent, GC-derived B-NHL, while it has no impact on the formation of MYC-driven, pre-GC lymphomas. Accordingly, abrogation of AID is associated with the disappearance of both CSR- and SHM-mediated structural alterations, including cMYC-IgH chromosomal translocations and aberrant SHM. These results demonstrate that AID is required for GC-derived lymphomagenesis, providing direct support to the notion that errors in AID-mediated antigen-receptor gene modification events represent major contributors to the pathogenesis of human B-NHL. Keywords: Phenotypic characterization of tumors developing in oncogene-driven mouse models of lymphomas

ORGANISM(S): Mus musculus

PROVIDER: GSE9249 | GEO | 2007/11/01

SECONDARY ACCESSION(S): PRJNA102863

REPOSITORIES: GEO

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Project description:The activation induced cytosine deaminase (AID) mediates diversification of B cell immunoglobulin genes by the three distinct yet related processes of somatic hypermutation (SHM), class switch recombination (CSR), and gene conversion (GCV). SHM occurs in germinal center B cells, and the transcription factor Bcl6 is a key regulator of the germinal center B cell gene expression program, including expression of AID. To test the hypothesis that Bcl6 function is important for the process of SHM, we compared WT chicken DT40 B cells, which constitutively perform SHM/GCV, to their Bcl6-deficient counterparts. We found that Bcl6-deficient DT40 cells were unable to perform SHM and GCV despite enforced high level expression of AID and substantial levels of AID in the nucleus of the cells. To gain mechanistic insight into the GCV/SHM dependency on Bcl6, transcriptional features of a highly expressed SHM target gene were analyzed in Bcl6-sufficient and -deficient DT40 cells. No defect was observed in the accumulation of single stranded DNA in the target gene as a result of Bcl6 deficiency. In contrast, association of Spt5, an RNA polymerase II (Pol II) and AID binding factor, was strongly reduced at the target gene body relative to the transcription start site in Bcl6-deficient cells as compared to WT cells. However, partial reconstitution of Bcl6 function substantially reconstituted Spt5 association with the target gene body but did not restore detectable SHM. Our observations suggest that in the absence of Bcl6, Spt5 fails to associate efficiently with Pol II at SHM targets, perhaps precluding robust AID action on the SHM target DNA. Our data also suggest, however, that Spt5 binding is not sufficient for SHM of a target gene even in DT40 cells with strong expression of AID. Sequencing of the IgL V region and mutationally active GFP transgene in WT, Bcl6-/- Pax5R, and Bcl6-/- Pax5R Bcl6R chicken DT40 cells for evidence of AID dependent mutations. ChIP-seq proiles of RNA Pol II, Spt5, and pSer5 Pol II at a GFP transgene in WT, Bcl6-/- Pax5R, and Bcl6-/- Pax5R Bcl6R chicken DT40 cells.

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Gene expression analysis of B-NHL from λMYC, λMYC/IµHABCL6, λMYC/AIDKO and λMYC/IµHABCL6/AIDKO mouse models

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