Vβ cluster sequences reduce the frequency of primary Vβ2 and Vβ14 rearrangements

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Abstract
T‐cell receptor (TCR) β variable region exons are assembled from numerous gene segments in a highly ordered and regulated manner. To elucidate mechanisms and identify cis‐acting elements that control Vβ rearrangement, we generated an endogenous TCR‐β allele with only the Vβ2, Vβ4, and Vβ14 segments. We found that αβ T lineage cells containing this Vβ2–4–14 allele and a wild‐type TCR‐β allele developed normally, but exhibited a significant increase in Vβ2+ and Vβ14+ cells. To quantify Vβ rearrangements on the Vβ2–4–14 allele, we generated αβ T‐cell hybridomas and analyzed TCR‐β rearrangements. Despite the deletion of almost all Vβ segments and 234 kb of Vβ cluster sequences, the Vβ2–4–14 allele exhibited only a slight decrease in Vβ rearrangement as compared with the wild‐type TCR‐β allele. Thus, cis‐acting control elements essential for directing Vβ rearrangement across large chromosomal distances are not located within the Vβ cluster. We also found a significant increase in the frequency of Vβ rearrangements involving Vβ2 and Vβ14, but not Vβ4, on the Vβ2–4–14 allele. Collectively, our data suggest that Vβ cluster sequences reduce the frequency of Vβ2 and Vβ14 rearrangements by competing with the productive coupling of accessible Vβ2 and Vβ14 segments with DJβ1 complexes.