EVIDENCE OF STAGE-SPECIFIC ELEMENT FOR GERM-LINE TRANSCRIPTION OF THETCR ALPHA-GENE LOCATED UPSTREAM OF J-ALPHA-49 LOCUS

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 germline tran scription of the TCR alpha gene which is closely associated with gene rearrangement. First, germ-line transcription of the TCR alpha gene in cluding the first segment of the J alpha locus, J alpha 49, was delaye d compared to that of the TCR beta gene in both normal and TCR-transge nic (Tg) mice. Furthermore, expression of this transcript could be ind uced by CD3 epsilon-mediated signals in recombination-activating gene (RAG)-2-deficient mice. In TCR-Tg mice, the endogenous J alpha 49 germ -line transcript could not yet be observed at the CD25(+) double-negat ive (DN) stage when the TCR alpha 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 hybrid oma expressed the J alpha 49 germ-line transcript. These data indicate that the J alpha 49 germ-line transcription occurs only at a specific developmental stage. Second, to determine which elements may be regul ating stage specificity, we performed transient transfection analysis with a reporter gene and demonstrated that the upstream region of the J alpha 49 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 alpha germ-line tran scripts is regulated in a stage-specific manner by a cis-element locat ed within the J alpha locus.