Deletion of the mouse T-cell receptor beta gene enhancer blocks alpha beta T-cell development

Intrathymic T-cell development requires temporally regulated rearrangement and expression of T-cell receptor (TCR) genes. To assess the role of the TCR beta gene transcriptional enhancer (E beta) in this process, mouse strains in which E beta is deleted were generated using homologous recombination techniques. We report that mice homozygous for the E beta deletion, whether a selectable marker gene is present or not, show a block in alpha beta T-cell development at the CD4(-)CD8(-) double-negative cell stage, whereas the number of gamma delta(+) T cells is normal, few CD4(+)CD8(+) double positive thymocytes and no alpha beta(+) T cells are produced. DNA-PCR and RNA-PCR analyses of thymic cells from homozygous mutants showed no evidence of TCR beta gene rearrangement although germ-line V beta transcripts were detected at a low level; in heterozygous T cells, the targeted allele is not rearranged. Thus, deletion of E beta totally prevents rearrangement, but not transcription, of the targeted beta locus. These data formally establish the critical role played by E beta in cis-activation of the TCR beta locus for V(D)J recombination during alpha beta T-cell development.