Project description:Activation-induced cytidine deaminase (AID) is required for both somatic hypermutation (SHM) and class-switch recombination (CSR) in activated B cells. AID is also known to target non-immunoglobulin genes and introduce mutations or chromosomal translocations, eventually causing tumors. To identify as-yet-unknown AID targets, we screened early AID-induced DNA breaks using two independent genome-wide approaches. Along with known AID targets, this screen identified a set of novel genes (SNHG3, MALAT1, BCL7A, and CUX1), and confirmed that these new loci accumulated mutations as high as Ig locus after AID activation. Moreover, these genes share three important characteristics with the immunoglobulin gene: translocations in tumors, repetitive sequences and the epigenetic modification of chromatin by H3K4 trimethylation in the vicinity of cleavage sites.
Project description:H3K4me3 plays a critical role in the activation-induced cytidine deaminase (AID)-induced DNA cleavage of switch (S) regions in the immunoglobulin heavy chain (IgH) locus during class-switch recombination (CSR). The histone chaperone complex facilitates chromatin transcription (FACT) is responsible for forming H3K4me3 at AID target loci. Histone chaperone suppressor of Ty6 (Spt6) also participates in regulating H3K4me3 for CSR and for somatic hypermutation (SHM) in AID target loci. H3K4me3 loss was correlated with defects in AID-induced DNA breakage and reduced mutation frequencies in IgH loci, in both S and variable regions, and in non-IgH loci, such as metastasis-associated lung adenocarcinoma transcript 1 (MALAT1) and small nucleolar RNA host gene 3 (SNHG3). Global gene expression analysis revealed that Spt6 can act as both a positive and negative transcriptional regulator in B cells, affecting approximately 5% of the genes that includes suppressor of Ty4 (Spt4) and AID. Interestingly, Spt6 regulates CSR and AID expression through two distinct histone modification pathways, H3K4me3 and H3K36me3, respectively. Spt6 is a unique histone chaperone, capable of regulating the histone epigenetic state of both AID targets and the AID locus. CH12F3-2A cells were transfected with control and Spt6 siRNAs; 24h later, cells were stimulated with CIT to induce CSR. Total RNA was extracted from control and Spt6 siRNA treated cells for mRNA expression profiling.
Project description:H3K4me3 plays a critical role in the activation-induced cytidine deaminase (AID)-induced DNA cleavage of switch (S) regions in the immunoglobulin heavy chain (IgH) locus during class-switch recombination (CSR). The histone chaperone complex facilitates chromatin transcription (FACT) is responsible for forming H3K4me3 at AID target loci. Histone chaperone suppressor of Ty6 (Spt6) also participates in regulating H3K4me3 for CSR and for somatic hypermutation (SHM) in AID target loci. H3K4me3 loss was correlated with defects in AID-induced DNA breakage and reduced mutation frequencies in IgH loci, in both S and variable regions, and in non-IgH loci, such as metastasis-associated lung adenocarcinoma transcript 1 (MALAT1) and small nucleolar RNA host gene 3 (SNHG3). Global gene expression analysis revealed that Spt6 can act as both a positive and negative transcriptional regulator in B cells, affecting approximately 5% of the genes that includes suppressor of Ty4 (Spt4) and AID. Interestingly, Spt6 regulates CSR and AID expression through two distinct histone modification pathways, H3K4me3 and H3K36me3, respectively. Spt6 is a unique histone chaperone, capable of regulating the histone epigenetic state of both AID targets and the AID locus.
Project description:Activation Induced Deaminase (AID) initiates somatic hypermutation (SHM) and class switch recombination (CSR) in germinal center (GC) B cells through the deamination of deoxycytidine residues (dC) into deoxyuridines (dU) in immunoglobulin (Ig) genes. Although AID has a strong preference for Ig genes, it can also target other genomic regions, giving rise to mutations or chromosomal translocations. Thus, understanding the specificity of AID has major implications for oncogenic transformation. However, approaching AID specificity has proved extremely challenging because AID deamination events occur at low frequencies. Here we have sequenced at very high depth >1500 genomic regions from GC B cells and identified 275 genes targeted by AID, including 30 of the previously known 35 AID targets. This has enabled for the first time to define the molecular features predictive of AID target specificity genome-wide. Furthermore, we identify the most highly mutated hotspot for AID activity described to date. We also find that Base Excision Repair (BER) and Mismatch Repair (MMR) systems, which are responsible for the resolution of AID deaminations, back-up each other to faithfully repair AID-induced lesions. Finally, our data establishes a novel link between AID mutagenic activity and malignant transformation.
Project description:Activation-induced deaminase (AID) initiates class switch recombination (CSR) and somatic hypermutation of immunoglobulin genes, which are required for efficient antibody responses. Collaterally, AID can also mutate a set of off-target genes with oncogenic consequences. The mechanisms that make such loci susceptible to AID are not fully understood. We find that the H3K79 histone methyltransferase DOT1L is located close to AID in the nucleus. Not only does DOT1L activity facilitate CSR, but it also facilitates AID off-target activity, including Igh-cMyc translocations. Genes mutated by AID display high DOT1L activity. DOT1L deficiency causes mostly increased nascent transcription, accompanied by a modest reduction in RNAPII occupancy. By integrating different genomic approaches, we discovered that DOT1L restricts the velocity of transcription elongation proportionally to the level of higher order H3K79 methylation (H3K79me2/3) and favors RNAPII pausing. These transcriptional conditions enhance AID occupancy and, consequently, its activity. Our data indicate a role for DOT1L and H3K79me2/3 in limiting transcription and highlight stronger RNAPII pausing and attenuated RNAPII elongation velocity as critical steps for productive AID association and mutagenesis at target loci. Furthermore, increased transcription elongation velocity could explain both upregulation and downregulation of genes in DOT1L-deficient cells.
Project description:Activation-induced deaminase (AID) initiates class switch recombination (CSR) and somatic hypermutation of immunoglobulin genes, which are required for efficient antibody responses. Collaterally, AID can also mutate a set of off-target genes with oncogenic consequences. The mechanisms that make such loci susceptible to AID are not fully understood. We find that the H3K79 histone methyltransferase DOT1L is located close to AID in the nucleus. Not only does DOT1L activity facilitate CSR, but it also facilitates AID off-target activity, including Igh-cMyc translocations. Genes mutated by AID display high DOT1L activity. DOT1L deficiency causes mostly increased nascent transcription, accompanied by a modest reduction in RNAPII occupancy. By integrating different genomic approaches, we discovered that DOT1L restricts the velocity of transcription elongation proportionally to the level of higher order H3K79 methylation (H3K79me2/3) and favors RNAPII pausing. These transcriptional conditions enhance AID occupancy and, consequently, its activity. Our data indicate a role for DOT1L and H3K79me2/3 in limiting transcription and highlight stronger RNAPII pausing and attenuated RNAPII elongation velocity as critical steps for productive AID association and mutagenesis at target loci. Furthermore, increased transcription elongation velocity could explain both upregulation and downregulation of genes in DOT1L-deficient cells.
Project description:Activation-induced deaminase (AID) initiates class switch recombination (CSR) and somatic hypermutation of immunoglobulin genes, which are required for efficient antibody responses. Collaterally, AID can also mutate a set of off-target genes with oncogenic consequences. The mechanisms that make such loci susceptible to AID are not fully understood. We find that the H3K79 histone methyltransferase DOT1L is located close to AID in the nucleus. Not only does DOT1L activity facilitate CSR, but it also facilitates AID off-target activity, including Igh-cMyc translocations. Genes mutated by AID display high DOT1L activity. DOT1L deficiency causes mostly increased nascent transcription, accompanied by a modest reduction in RNAPII occupancy. By integrating different genomic approaches, we discovered that DOT1L restricts the velocity of transcription elongation proportionally to the level of higher order H3K79 methylation (H3K79me2/3) and favors RNAPII pausing. These transcriptional conditions enhance AID occupancy and, consequently, its activity. Our data indicate a role for DOT1L and H3K79me2/3 in limiting transcription and highlight stronger RNAPII pausing and attenuated RNAPII elongation velocity as critical steps for productive AID association and mutagenesis at target loci. Furthermore, increased transcription elongation velocity could explain both upregulation and downregulation of genes in DOT1L-deficient cells.
Project description:Activation-induced deaminase (AID) initiates class switch recombination (CSR) and somatic hypermutation of immunoglobulin genes, which are required for efficient antibody responses. Collaterally, AID can also mutate a set of off-target genes with oncogenic consequences. The mechanisms that make such loci susceptible to AID are not fully understood. We find that the H3K79 histone methyltransferase DOT1L is located close to AID in the nucleus. Not only does DOT1L activity facilitate CSR, but it also facilitates AID off-target activity, including Igh-cMyc translocations. Genes mutated by AID display high DOT1L activity. DOT1L deficiency causes mostly increased nascent transcription, accompanied by a modest reduction in RNAPII occupancy. By integrating different genomic approaches, we discovered that DOT1L restricts the velocity of transcription elongation proportionally to the level of higher order H3K79 methylation (H3K79me2/3) and favors RNAPII pausing. These transcriptional conditions enhance AID occupancy and, consequently, its activity. Our data indicate a role for DOT1L and H3K79me2/3 in limiting transcription and highlight stronger RNAPII pausing and attenuated RNAPII elongation velocity as critical steps for productive AID association and mutagenesis at target loci. Furthermore, increased transcription elongation velocity could explain both upregulation and downregulation of genes in DOT1L-deficient cells.