Evidence of stage-specific element for germ-line transcription of the TCR α gene located upstream of Jα49 locus

Abstract

T cell receptor (TCR) genes are rearranged and expressed in an ordered manner during T cell development. The basic mechanism regulating this stepwise DNA alteration is poorly understood. To address this issue, we explored the presence of a stage-specific element for germ-line transcription of the TCR α gene which is closely associated with gene rearrangement. First, germ-line transcription of the TCR α gene including the first segment of the Jet locus, Jα49, was delayed compared to that of the TCR β gene in both normal and TCR-transgenic (Tg) mice. Furthermore, expression of this transcript could be induced by CD3ε-mediated signals in recombination-activating gene (RAG)-2-deficient mice. In TCR-Tg mice, the endogenous Jα49 germ-line transcript could not yet be observed at the CD25+ double-negative (DN) stage when the TCR α transgene was expressed. Of immature T cell hybridomas derived from either scid thymocytes (CD25+ DN) or immature CD8-single positive (ISP) thymocytes, only the latter hybridoma expressed the Jα49 germ-line transcript. These data indicate that the Jα49 germ-line transcription occurs only at a specific developmental stage. Second, to determine which elements may be regulating stage specificity, we performed transient transfection analysis with a reporter gene and demonstrated that the upstream region of the Jα49 locus possesses promoter activity in correlation with germ-line transcription in ISP-derived but not in SCID-derived hybridomas. These results indicate that the expression of TCR α germ-line transcripts is regulated in a stage-specific manner by a cis-element located within the Jα locus.