Generation and resolution of DNA double-strand breaks is required to assemble antigen-specific receptors from the genes encoding V, D, and J gene segments during recombination. The present report investigates the requirement for ataxia telangiectasia-mutated (ATM) kinase, a component of DNA double-strand break repair, during TCRâ recombination and in subsequent TCRâ-dependent repertoire generation and thymocyte development. CD4(-)CD8(-) double negative stage 2/3 thymocytes from ATM-deficient mice have both an increased frequency of cells with DNA break foci at TCRâ loci and reduced Vâ-DJâ rearrangement. Sequencing of TCRâ complementarity-determining region 3 demonstrates that ATM-deficient CD4(+)CD8(+) double positive thymocytes and peripheral T cells have altered processing of coding ends for both in-frame and out-of-frame TCRâ rearrangements, providing the unique demonstration that ATM deficiency alters the expressed TCRâ repertoire by a selection-independent mechanism. ATMKO thymi exhibit a partial developmental block in DN cells as they negotiate the â-selection checkpoint to become double negative stage 4 and CD4(+)CD8(+) thymocytes, resulting in reduced numbers of CD4(+)CD8(+) cells. Importantly, expression of a rearranged TCRâ transgene substantially reverses this defect in CD4(+)CD8(+) cells, directly linking a requirement for ATM during endogenous TCRâ rearrangement to subsequent TCRâ-dependent stages of development. These results demonstrate that ATM plays an important role in TCRâ rearrangement, generation of the TCRâ CDR3 repertoire, and efficient TCRâ-dependent T cell development.
Animals Ataxia Telangiectasia Mutated Proteins