title: Beyond the 12/23 rule of VDJ recombination independent of the Rag proteins.
abstract: The combinatorial repertoire of AgRs is established through somatic recombination of V, D, and J gene segments during lymphocyte development. Incorporation of D segments into IgH, TCRbeta, and TCRdelta chains also contributes to junctional diversification by substantially extending the length of the third CDR. The V, D, and J gene segments are flanked by recombination signals (RS) of 12- or 23-mer spacer length that direct recombination according to the 12/23 rule. D genes in the TCRbeta and TCRdelta loci are flanked by a 12RS and 23RS, and their incorporation is controlled by mechanisms "beyond the 12/23 rule." In the TCRbeta locus, selective interactions between Rag proteins and the RS flanking the V-D and D-J genes, respectively, are sufficient to enforce D gene usage. In this article, we report that in the TCRdelta locus, the Rag proteins are not the major determinant of D gene incorporation. In developing mouse and human thymocytes, the two Ddelta genes rearrange predominantly to form D-D coding joints. In contrast, when tested in ex vivo transfection assays in a nonlymphoid cell line, the flanking RS mediate deletion, rather than incorporation, of the two D genes on both exogenous recombination substrates and the endogenous locus. These results suggest that selective Rag-RS interactions are not the sole regulators of D gene segment incorporation, and additional, perhaps lymphocyte-specific, mechanisms exist that allow proper shaping of the primary AgR repertoire.
authors.affiliation: Department of Microbiology and Immunology, Graduate Program in Molecular and Cellular Biology, University of Maryland School of Medicine, Baltimore, MD 21201, USA.
authors.forename: Alexandru
authors.initials: A
authors.lastname: Olaru
authors.forename: Howard T
authors.initials: HT
authors.lastname: Petrie
authors.forename: Ferenc
authors.initials: F
authors.lastname: Livák
mesh_terms: D000818:Animals; D002454:Cell Differentiation / Q000235:genetics / Q000276:immunology; D002460:Cell Line; D004268:DNA-Binding Proteins / Q000235:genetics*; D015329:Gene Rearrangement, T-Lymphocyte; D019676:Genes, T-Cell Receptor delta; D005819:Genetic Markers / Q000276:immunology; D018398:Homeodomain Proteins / Q000235:genetics*; D006801:Humans; D007133:Immunoglobulin Joining Region / Q000235:genetics*; D007135:Immunoglobulin Variable Region / Q000235:genetics*; D007700:Kinetics; D051379:Mice; D008810:Mice, Inbred C57BL; D009687:Nuclear Proteins; D021382:Protein Sorting Signals / Q000235:genetics; D016692:Receptors, Antigen, T-Cell, gamma-delta / Q000235:genetics; D011995:Recombination, Genetic; D013601:T-Lymphocytes / Q000166:cytology / Q000276:immunology / Q000378:metabolism; D013950:Thymus Gland / Q000166:cytology / Q000276:immunology / Q000378:metabolism; D014162:Transfection
chemical_list: D004268:DNA-Binding Proteins; D005819:Genetic Markers; D018398:Homeodomain Proteins; D007133:Immunoglobulin Joining Region; D007135:Immunoglobulin Variable Region; D009687:Nuclear Proteins; D021382:Protein Sorting Signals; C499311:RAG2 protein, human; C499308:Rag2 protein, mouse; D016692:Receptors, Antigen, T-Cell, gamma-delta; C064655:V(D)J recombination activating protein 2; C064658:RAG-1 protein