Genes encoding the T-cell receptor alpha and beta subunits are transcribed in an ordered manner during intrathymic ontogeny.

To further characterize sequential events involved in activation of genes encoding the T-cell receptor (a complex of T3 molecules and a disulfide-linked heterodimer designated Ti, T3-Ti) for antigen and the major histocompatibility complex during intrathymic ontogeny, cDNA probes specific for Ti alpha and Ti beta subunits were used for transcriptional analysis. Ti beta transcript levels were minimal in stage I thymocytes, maximal in stage II thymocytes, and intermediate in state III thymocytes. In contrast, Ti alpha transcriptional activity was virtually undetectable in stage I, was low in stage II, and achieved high levels only in the stage III compartment. Analysis of tumor populations derived from individual stages of thymic differentiation confirmed these observations and demonstrated that clonal stage I-II cells often express Ti beta RNA in the absence of Ti alpha RNA. The latter was not a consequence of functional Ti alpha-subunit isotypy because each of 13 interleukin 2-dependent T-cell clones, including inducer, suppressor, and cytotoxic T cells, contain transcripts that hybridize with the Ti alpha probe. From these data it is concluded that Ti beta gene activation precedes Ti alpha gene activation. Moreover, the high level of Ti beta mRNA preceding Ti alpha mRNA expression implies that Ti beta mRNA and/or its protein products may regulate Ti alpha gene transcription.