Positive and negative regulation of V(D)J recombination by the E2A proteins

A key feature of B and T lymphocyte development is the generation of antige n receptors through the rearrangement and assembly of the germline variable (V), diversity (D), and joining (J) gene segments. However, the mechanisms responsible for regulating developmentally order-ed gene rearrangements ar e largely unknown. Here we show that the E2A gene products are essential fo r the proper coordinated temporal regulation of V(D)J rearrangements within the T cell receptor (TCR) gamma and delta loci. Specifically, we show that E2A is required during adult thymocyte development to inhibit rearrangemen ts to the gamma and delta V regions that normally recombine almost exclusiv ely during fetal thymocyte development. The continued rearrangement of the fetal V gamma 3 gene segment in E2A-deficient adult thymocytes correlates w ith increased levels of V gamma 3 germline transcripts and increased levels of double-stranded DNA breaks at the recombination signal sequence borderi ng V gamma 3. Additionally, rearrangements to a number of V gamma and V del ta gene segments used predominantly during adult development are significan tly reduced in E2A-deficient thymocytes. Interestingly, at distinct stages of T lineage development, both the increased and decreased rearrangement of particular V delta gene segments is highly sensitive to the dosage of the E2A gene products, suggesting that the concentration of the E2A proteins is rate limiting for the recombination reaction involving these V delta regio ns.