Germline transcription from T-cell receptor Vβ gene is uncoupled from allelic exclusion

Allelic exclusion operates in B and T lymphocytes to ensure clonal expression of antigen receptors after V(D) J recombination. Germline transcription, which proceeds V(D) J recombination, has been postulated to provide an instructive signal for allelic exclusion. Here, we use a genetic marker to track germline transcription from a V beta gene within the TCRb locus. We find that developing thymocytes exhibit uniformed, bi-allelic activation of the V beta gene before V-DJ recombination, a process subject to allelic exclusion. We further show that V-DJ rearrangement promotes activation rather than silencing of germline transcription from the remaining V beta genes on either the functionally or non- functionally rearranged chromosome. Results presented here suggest that germline transcription, although necessary for V(D) J recombination, is not sufficient to instruct allelic exclusion.