Regulation of T cell receptor gene assembly by local and long-range changes in chromatin accessibility

Abstract

Antigen receptor gene assembly is governed by transcriptional promoters and enhancers that communicate over large distances and modulate chromatin accessibility to V(D)J recombinase. The precise role of these cis-acting elements in opening chromatin at recombinase targets and the mechanisms underlying their collaboration remain unclear. I show that the TCR beta enhancer (Ebeta) directs long-range chromatin opening over both DbetaJbeta clusters. Strikingly, chromatin associated with the Dbeta1 gene segment is refractory to Ebeta-mediated opening. Accessibility at Dbeta1 is accompanied by the formation of a stable holocomplex between a Dbeta-proximal promoter, PDbeta1, and Ebeta. These findings indicate a stepwise process for DbetaJbeta recombination that relies on distinct aspects of Ebeta activity: an intrinsic function that directs general chromatin opening and a cooperative function with PDbeta1 that facilitates the unmasking of the Dbeta1 gene segment, triggering TCR beta gene assembly.