Recombination signal sequences shape antigen receptor repertoires and enforce allelic exclusion

• Published in: The Journal of immunology (1950) Vol. 198; no. 1_Supplement; pp. 212 - 212.12
• Main Authors: Wu, Glendon S, Yang-Iott, Katherine S, Bassing, Craig H
• Format: Journal Article
• Language: English
• Published: 01-05-2017
• ISSN: 0022-1767; 1550-6606
• DOI: 10.4049/jimmunol.198.Supp.212.12

Abstract
Antigen receptor loci are arrays of variable (V), diversity (D), and joining (J) gene segments that the RAG endonuclease assembles into complete AgR genes. RAG binds to and cleaves at recombination signal sequences (RSSs) that flank gene segments. V(D)J recombination of Tcrb, Igh, and Igk loci is regulated such that functional AgR genes are assembled on and expressed from one allele (allelic exclusion) in most cells. It is assumed that allelic exclusion is achieved by mono-allelic initiation and feedback inhibition of the V-to-(D)J recombination step, and intrinsic features of RSSs have been proposed to mediate mono-allelic V-to-DJ recombination of Tcrb and Igh loci. We established and analyzed mice with the Trbv2 or Trbv31 RSS replaced by an RSS that possesses greater intrinsic recombination activity. Each of these RSS substitutions causes a profound increase in the development of T cells expressing either Trbv2+ or Trbv31+ TCRβ chains, reflecting that the RSSs flanking Trbv segments are major determinants of Trbv recombination frequency. Each RSS replacement also promotes a modest increase in the fraction of cells expressing Trbv2+ or Trbv31+ TCRβ chains along with another type of TCRβ chain (allelic inclusion). Strikingly, mice with Trbv2 and Trbv31 RSS replacements on opposite alleles have a 30-fold higher than normal level of allelic inclusion for Trbv2+ and Trbv31+ TCRβ chains, demonstrating that RSSs flanking Trbv segments enforce TCRβ allelic exclusion. We conclude that the infrequency of Trbv recombination as determined by inherent inefficiencies of Trbv RSSs limits bi-allelic assembly of Tcrb genes within the time window before feedback inhibition permanently cements allelic exclusion.