Immune defect in ataxia telangiectasia patients has been attributed to either the failure of V(D)J recombination or class-switch recombination, and the chromosomal translocation in their lymphoma often involves the TCR gene. The ATM-deficient mouse exhibits fewer CD4 and CD8 single-positive T cells because of a failure to develop from the CD4+CD8+double-positive phase to the single-positive phase. Although the occurrence of chromosome 14 translocations involving TCR-δ gene in ATM-deficient lymphomas suggests that these are early events in T-cell development, a thorough analysis focusing on early T-cell development has never been performed. Here we demonstrate that ATM-deficient mouse thymocytes are perturbed in passing through the β- or γδ-selection checkpoint, leading in part to the developmental failure of T cells. Detailed karyotype analysis using the in vitro thymocyte development system revealed that RAG-mediated TCR-α/δlocus breaks occur and are left unrepaired during the troublesome β- or γδ- selection checkpoints. By getting through these selection checkpoints, some of the clones with random or nonrandom chromosomal translocations involving TCR- α/δ locus are selectedandaccumulate. Thus, our study visualized the first step of multi-step evolutions toward lymphomagenesis inATM-deficient thymocytes associated with T-lymphopenia and immunodeficiency.
All Science Journal Classification (ASJC) codes
- Cell Biology