TCRβ Feedback Signals Inhibit the Coupling of Recombinationally Accessible Vβ14 Segments with DJβ Complexes

Abstract

Ag receptor allelic exclusion is thought to occur through monoallelic initiation and subsequent feedback inhibition of recombinational accessibility. However, our previous analysis of mice containing a V(D)J recombination reporter inserted into Vβ14 (Vβ14[superscript Rep]) indicated that Vβ14 chromatin accessibility is biallelic. To determine whether Vβ14 recombinational accessibility is subject to feedback inhibition, we analyzed TCRβ rearrangements in Vβ14[superscript Rep] mice containing a preassembled in-frame transgenic Vβ8.2Dβ1Jβ1.1 or an endogenous Vβ14Dβ1Jβ1.4 rearrangement on the homologous chromosome. Expression of either preassembled VβDJβC β-chain accelerated thymocyte development because of enhanced cellular selection, demonstrating that the rate-limiting step in early αβ T cell development is the assembly of an in-frame VβDJβ rearrangement. Expression of these preassembled VβDJβ rearrangements inhibited endogenous Vβ14-to-DJβ rearrangements as expected. However, in contrast to results predicted by the accepted model of TCRβ feedback inhibition, we found that expression of these preassembled TCR β-chains did not downregulate recombinational accessibility of Vβ14 chromatin. Our findings suggest that TCRβ-mediated feedback inhibition of Vβ14 rearrangements depends on inherent properties of Vβ14, Dβ, and Jβ recombination signal sequences.