DIFFERENTIAL ACTIVATION OF TRANSCRIPTION VERSUS RECOMBINATION OF TRANSGENIC T-CELL RECEPTOR-BETA VARIABLE REGION GENE SEGMENTS IN B-LINEAGE AND T-LINEAGE CELLS

We have tested the ability of the T cell receptor beta (TCR-beta) transcriptional enhancer (E(beta)) to confer transcriptional activation and tissue-specific V(D)J recombination of TCR-beta V, D, and J segments in a transgenic minilocus recombination substrate. We find that the minimal E(b)eta element, as previously shown for a DNA segment that contained the E mu element, promotes a high level of substrate D to J(beta) rearrangement in both B and T cells, but only promotes V-beta to DJ beta rearrangement in T cells. Thus, both the E(mu) and E(beta) elements similarly direct V(D)J recombination of this substrate in vivo, supporting a general role for transcriptional enhancers in the normal regulation of this rearrangement process. Surprisingly, however, we found that both the V-beta and DJ(beta) portion of the constructs were transcribed in an enhancer-dependent fashion (conferred by either E(mu) or E(beta)) in both B and T lineage cells, including normal precursor B cells propagated in culture. These findings indicate that, at least in some contexts, transcriptional activation, per se, is not sufficient to confer V(D)J recombinational accessibility to a substrate V gene segment,