The TCRβ enhancer is dispensable for the expression of rearranged TCRB genes in thymic DN2/DN3 populations but not at later stages

The E beta enhancer has been shown to be dispensable for germline transcription of nonrearranged TCR beta segments but appears to be required for TCR beta V to DJ rearrangement. E beta dependency of the subsequent expression of VDJ-rearranged TCR beta)3 genes in thymic subpopulations has so far not been analyzed. We generated transgenic mice, using a V beta 8.2D beta 1.3-rearranged TCR beta bacterial artificial chromosome, which lacked E beta, and monitored transgene expression by flow cytometry using V beta-specific mAbs and an IRES-eGFP reporter. Transgene expression was found in double negative (DN)2 and DN3 but not at later stages of thymopoesis. There was no toxicity associated with the transgene given that apoptosis in DN3, DN4 was not increased, and the number of DN4 cells generated from DN3 cells in reaggregate thymic organ cultures was not diminished. The transgenic TCR beta gave rise to a pre-TCR, as suggested by its ability to suppress endogenous TCRP rearrangement, to facilitate beta-selection on a TCR beta-deficient background and to inhibit gamma delta T cell lineage development. The results suggest that the V beta 8.2 promoter is sufficient to drive expression of rearranged TCR beta VDJ genes E beta independently in DN2/DN3 but not at later stages.