TCR Feedback Signals Inhibit the Coupling of Recombinationally Accessible V14 Segments with DJ Complexes

Antigen receptor allelic exclusion is thought to occur through mono-allelic initiation and subsequent feedback inhibition of recombinational accessibility. However, our previous analysis of mice containing a V(D)J recombination reporter inserted into Vβ14 (Vβ14Rep) indicated that Vβ14 chromatin accessibility is bi-allelic. To determine whether Vβ14 recombinational accessibility is subject to feedback inhibition, we analyzed TCRβ rearrangements in Vβ14Rep mice containing a preassembled in frame transgenic Vβ8.2Dβ1Jβ1.1 or an endogenous Vβ14Dβ1Jβ1.4 rearrangement on the homologous chromosome. Expression of either pre-assembled VβDJβCβ chain accelerated thymocyte development due to 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 pre-assembled 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 pre-assembled TCRβ chains did not down-regulate recombinational accessibility of Vβ14 chromatin. Our findings suggest that TCRβ mediated feedback inhibition of Vβ14 rearrangements depends upon inherent properties of Vβ14, Dβ, and Jβ recombination signal sequences.