The T cell receptor β (TCRβ) locus contains three gene segment families, variable (V), diversity (D) and joining (J), each of which contributes one segment to form a TCRβ exon. In DN2 stage thymocytes, a Dβ segment joins a Jβ segment on both alleles, while in the DN3 stage Vβ segments join with previously formed DJβ complexes. Formation of a productive (protein encoding) VDJβ complex on one allele is theorized to prevent Vβ segments from joining with DJβ complexes on the other allele, leading to TCRβ allelic exclusion. To elucidate mechanisms that regulate Vβ joining and TCRβ allelic exclusion, we generated and analyzed mice with a recombination reporter cassette consisting of the Dβ1 and Jβ1.1 gene segments inserted into the endogenous Vβ14 segment. We found Vβ14DJrecombination initiated concurrent with Vβ14 rearrangement, suggesting local chromatin environment determines the developmental timing of Vβ14 rearrangement. Our analysis of Vβ14DJ/WT and Vβ14DJ/DJ αβ T cell hybridomas revealed that Vβ14DJrecombination occurs at a substantially higher frequency than Vβ14 joining. Moreover, our initial findings indicate that Vβ14DJrecombination is not inhibited by expression of a productive VDJβ complex. Collectively, these data suggest that modulation of Vβ14 recombinational accessibility is neither the rate-limiting or regulated step in joining of Vβ14 segments with DJβ complexes.

Training Grant: 5-T32-Al055428