TCRbeta formation: Vbeta accessibility is not the limiting or regulated step (B8)

The T cell receptor β (TCR_β) locus contains three gene segment families, variable (V), diversity (D) and joining (J), each of which contributes one segment to form a TCR_β exon. In DN2 stage thymocytes, a D_β segment joins a J_β segment on both alleles, while in the DN3 stage V_β segments join with previously formed DJ_β complexes. Formation of a productive (protein encoding) VDJ_β complex on one allele is theorized to prevent V_β segments from joining with DJ_β complexes on the other allele, leading to TCR_β allelic exclusion. To elucidate mechanisms that regulate V_β joining and TCR_β allelic exclusion, we generated and analyzed mice with a recombination reporter cassette consisting of the D_β1 and J_β1.1 gene segments inserted into the endogenous V_β14 segment. We found V_β14^DJrecombination initiated concurrent with V_β14 rearrangement, suggesting local chromatin environment determines the developmental timing of V_β14 rearrangement. Our analysis of V_β14^DJ/WT and V_β14^DJ/DJ αβ T cell hybridomas revealed that V_β14^DJrecombination occurs at a substantially higher frequency than V_β14 joining. Moreover, our initial findings indicate that V_β14^DJrecombination is not inhibited by expression of a productive VDJ_β complex. Collectively, these data suggest that modulation of V_β14 recombinational accessibility is neither the rate-limiting or regulated step in joining of V_β14 segments with DJ_β complexes.

Training Grant: 5-T32-Al055428