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[摘要]：The pre-T-cell receptor (TCR) is crucial for the early T-cell development, but the ligand for pre-TCR remains unidentified. We recently proposed a model that pre-TCR complexes oligomerize spontaneously through interactions of the pre-TCR alpha chain. To investigate the mechanism underlying this ligand-independent signaling in vivo, we established knock-in mice that express a pre-TCRa mutant lacking charged amino acids ((DRRR117)-R-22-R-24-R-102 to A(22)A(24)A(102)A(11)7;4A). CD4(+)CD8(+) thymocyte number was significantly reduced in invariant pre-TCRa (pT alpha(4A/4A)) mice, whereas CD4(-)CD8(-) thymocytes were unaffected. The percentages of double-negative 3 (DN3) cells and gamma delta T cells were increased in the pT alpha(4A/4A) thymus, indicating that beta-selection is impaired in pT alpha(4A/4A) mice. Pre-TCR-mediated tyrosine phosphorylation and clonal expansion into double-positive thymocytes were also defective in the knock-in mice. Pre-TCR was expressed at higher levels on pT alpha(4A/4A) cell surfaces than on those of the wild type, suggesting that the charged residues in pT alpha are critical for autonomous engagement and subsequent internalization of pre-TCR. Pre-TCR-mediated allelic exclusion of the TCR beta gene was also inhibited in pT alpha(4A/4A) mice, and thereby, dual TCR beta s were expressed on pT alpha(4A/4A) T cells. Furthermore, the TCR beta chain variable region (V beta) repertoire of mature T cells was significantly altered in pT alpha(4A/4A) mice. These results suggest that charged residues of pT alpha are critical for beta-selection, allelic exclusion, and TCR beta repertoire formation. |
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