E proteins are required to activate germline transcription of the TCR Vβ8.2 gene

Each TCR Vβ gene is regulated by an individual Vβ promoter, which becomes active prior to V(D) J recombination and drives germline transcription. It has been shown that Vβ gene locus activation and recombination are dependent on the Vβ promoter. However, transcription factors that regulate Vβ germline transcription remain largely undefined. A major challenge in studying Vβ gene germline transcription is the quantitative assessment of relatively low-level transcripts in T-cell progenitors. Here we used the established Vβ8.2CD² knock-in mouse model to assess functions of E-protein transcription factors in Vβ8.2 germline transcription. We show that E proteins are required for the activation but not the maintenance of the Vβ8.2 germline transcription during thymocyte development. The activation of Vβ8.2 germline transcription depends more on the E proteins encoded by the E2A gene than by the HEB gene. We further show that IL-7 receptor (IL-7R)-mediated signals are essential for Vβ8.2 germline transcription. We provide evidence that IL-7R expression is only partially controlled by E2A, suggesting a role for E2A in driving Vβ8.2 germline transcription independent of IL-7R activation.