Genetic and Epigenetic Control of V Gene Rearrangement Frequency

We show that the physical distribution of nucleosomes at antigen receptor loci is subject to regulated cell type-specific and lineagespecific positioning and correlates with the accessibility of these gene segments to recombination. At the Ig heavy chain locus (IgH), a nucleosome in pro-B cells is generally positioned over each IgH variable (VH) coding segment, directly adjacent to the recombination signal sequence (RSS), placing the RSS in a position accessible to the recombination activating gene (RAG) recombinase. These changes result in establishment of a specific chromatin organization at the RSS that facilitates accessibility of the genomic DNA for the RAG recombinase. In contrast, in mouse embryonic fibroblasts the coding segment is depleted of nucleosomes, which instead cover the RSS, thereby rendering it inaccessible. Pro-T cells exhibit a pattern intermediate between pro-B cells and mouse embryonic fibroblasts. We also find large-scale variations of nucleosome density over hundreds of kilobases, delineating chromosomal domains within IgH, in a cell typedependent manner. These findings suggest that developmentally regulated changes in nucleosome location and occupancy, in addition to the known chromatin modifications, play a fundamental role in regulating V(D)J recombination. Nucleosome positioning-which has previously been observed to vary locally at individual enhancers and promoters-may be a more general mechanism by which cells can regulate the accessibility of the genome during development, at scales ranging from several hundred base pairs to many kilobases.T he diverse repertoire of antigen receptors in vertebrates is generated by an ordered series of somatic site-specific DNA rearrangement events, collectively termed V(D)J recombination. Antigen receptor genes are assembled from V, D, and J gene segments organized into seven different loci [T-cell receptor (TCR) α, β, γ, and δ, and Ig H, κ, and λ], each of which undergoes a series of recombination reactions to generate a functional TCR or B-cell receptor (BCR) (1, 2) Rearrangement is lineage-specific, such that BCR genes are fully rearranged only in B cells and TCR genes are assembled only in T cells. Rearrangement also occurs in a preferred temporal order. For example, at the human and murine IgH loci, joining of D to J segments precedes V to DJ joining, and IgH joining precedes joining at Igκ (or Igλ) (3). In addition, recombination at several loci shows "allelic exclusion": Functional VDJH or VJκ/Jλ joining occurs only on one allele (4).Recombination is initiated by the lymphocyte-specific recombination activating gene (RAG)1/RAG2 endonuclease. RAG1/2 cleaves at the recombination signal sequences (RSSs) flanking all antigen receptor gene segments. The consensus RSS consists of a heptamer sequence directly adjacent to the coding element and an A/T-rich nonamer separated from the heptamer by a spacer region of conserved length (12 or 23 bp) but relatively nonconserved sequence. The broken ends are then joined with the aid of DNA repair proteins,...

Section: Resultssupporting

confidence: 55%

Section: Resultsmentioning

confidence: 97%

Regulated large-scale nucleosome density patterns and precise nucleosome positioning correlate with V(D)J recombination

Pulivarthy

Lion

Kuzu

et al. 2016

“…Studies in V-gene use variation in inbred mouse strains suggest that the regulatory mechanisms may represent a more general mechanism for maintaining V-gene diversity in a population (44). A complete characterization of heritable mechanisms should consider haplotype architecture, cis-regulatory elements, copy-number variation, and even transregulatory elements that may influence segment selection (33,45). Despite common segment-use profiles, the CDR-H3 repertoires remained highly personal to each individual in the study.…”

Section: Discussionmentioning

confidence: 93%

Naive antibody gene-segment frequencies are heritable and unaltered by chronic lymphocyte ablation

Glanville

Kuo²,

Büdingen³

et al. 2011

179

212

A diverse antibody repertoire is essential for an effective adaptive immune response to novel molecular surfaces. Although past studies have observed common patterns of V-segment use, as well as variation in V-segment use between individuals, the relative contributions to variance from genetics, disease, age, and environment have remained unclear. Using high-throughput sequence analysis of monozygotic twins, we show that variation in naive V H and D H segment use is strongly determined by an individual's germ-line genetic background. The inherited segment-use profiles are resilient to differential environmental exposure, disease processes, and chronic lymphocyte depletion therapy. Signatures of the inherited profiles were observed in class switched germ-line use of each individual. However, despite heritable segment use, the rearranged complementarity-determining region-H3 repertoires remained highly specific to the individual. As it has been previously demonstrated that certain V-segments exhibit biased representation in autoimmunity, lymphoma, and viral infection, we anticipate our findings may provide a unique mechanism for stratifying individual risk profiles in specific diseases.heritable variation | next generation sequencing | V-gene S pecific biases in the antibody repertoire have been found in many diseases, from viral infections to cancers to autoimmune disorders (1-15). Although it is possible that heritable variation in the composition of the antibody repertoire could alter inherent risk to specific diseases, the diversity of the antibody repertoire has hindered direct characterization of heritable influences.Early twin studies provided some evidence of genetic variation affecting reactive titers from the antibody repertoire. Multiple studies observed both total Ig and antigen-specific titers to be more correlated in monozygotic twins than dizygotic twins or unrelated individuals (16)(17)(18). In some cases of monozygotic twins discordant for autoimmune diseases, the healthy twin often shared high autoantibody reactive titers with their affected twin (16,19,20).Early sequencing studies were able to identify some systematic biases in the antibody repertoire with limited sampling depth. The first sequencing studies to characterize V(D)J diversification mechanisms identified the gene segment recombination process, but also implied a repertoire too diverse to exhaustively interrogate by traditional sequencing technologies (21). Complete characterization of V-segment loci established ∼50 V H , 40 V κ , and 30 V λ segments in an individual, with a number of allelic variants for the majority of segments (22)(23)(24). Evaluation of use across individuals revealed biased V-gene representation that preceded selection (25)(26)(27). Quantitative PCR of V-gene families showed family use largely stable over time, with fluctuations in use correlated to antigen-specific responses (28). In the T-cell receptor (TCR) repertoire, TCRB-V use was more highly correlated in healthy monozygotic twins than unrelated individua...

“…Chromatin accessibility at gene segments has been studied extensively as a determinant of the tissue-and stagespecific mechanisms controlling V(D)J recombination (6,7). Germ-line transcription of gene segments leads to the deposition of H3K4me3, a histone modification that is recognized by RAG2 and augments endonuclease function of the RAG complex (8,9,45).…”

Section: Role Of Chromatin Environment In Determining Vβ Recombinationmentioning

confidence: 99%

“…Even within an AgR locus, gene segment recombination is ordered, with D-J rearrangements preceding V-DJ. Numerous studies support a key role for chromatin accessibility in determining the recombination potential of gene segments (7). The primary RAG-1/2 targets in a given cell type are transcriptionally active and DNase hypersensitive, two hallmarks of accessible chromatin.…”

mentioning

confidence: 99%

Unifying model for molecular determinants of the preselection Vβ repertoire

Gopalakrishnan

Majumder

Predeus

et al. 2013

Self Cite

The primary antigen receptor repertoire is sculpted by the process of V(D)J recombination, which must strike a balance between diversification and favoring gene segments with specialized functions. The precise determinants of how often gene segments are chosen to complete variable region coding exons remain elusive. We quantified Vβ use in the preselection Tcrb repertoire and report relative contributions of 13 distinct features that may shape their recombination efficiencies, including transcription, chromatin environment, spatial proximity to their DβJβ targets, and predicted quality of recombination signal sequences (RSSs). We show that, in contrast to functional Vβ gene segments, all pseudo-Vβ segments are sequestered in transcriptionally silent chromatin, which effectively suppresses wasteful recombination. Importantly, computational analyses provide a unifying model, revealing a minimum set of five parameters that are predictive of Vβ use, dominated by chromatin modifications associated with transcription, but largely independent of precise spatial proximity to DβJβ clusters. This learned model-building strategy may be useful in predicting the relative contributions of epigenetic, spatial, and RSS features in shaping preselection V repertoires at other antigen receptor loci. Ultimately, such models may also predict how designed or naturally occurring alterations of these loci perturb the preselection use of variable gene segments.lymphocytes | T-cell receptor | gene regulation G ene activity is regulated at multiple levels to coordinate expression during development. At a most basic level, the collection of cis-acting elements for a genetic locus recruits transcription factors that alter its chromatin environment to either induce or repress gene activity. Emerging studies indicate that the 3D conformation of a locus also plays an important role in the regulation of its composite genes (1). At most genes, many levels of control are integrated to achieve the requisite gene expression state. For example, transcriptional promoters interact with their cognate enhancers over considerable distances in the linear genome to generate "hubs" where the two cis elements are in spatial proximity (1, 2).All of these regulatory strategies are used to generate functional Ig (Ig) and T-cell receptor (Tcr) genes during lymphocyte development (3). Each antigen receptor (AgR) locus is composed of multiple variable (V), joining (J), and sometimes diversity (D) gene segments that are assembled by the process of V (D)J recombination, creating a potential variable region exon (4). Recombination is mediated by the RAG-1/2 enzymatic complex, which is expressed in all developing lymphocytes and recognizes semiconserved recombination signal sequences (RSSs) flanking all AgR gene segments (5). On selection of two compatible gene segments by RAG-1/2, recombination proceeds via a DNA break/repair mechanism, ultimately fusing the two selected segments (4, 5).The assembly of AgR genes is strictly regulated despite a common collection of ge...