Expression of T-cell antigen receptor genes during fetal development in the thymus.

The T-cell antigen receptor is a heterodimeric molecule composed of alpha- and beta-subunits of relative molecular mass 40,000-50,000 (refs 1-6). Recently, the genes encoding both the beta- and alpha- chains have been cloned. By comparing amino-acid and nucleic-acid sequences, it is clear that these genes encode the alpha- and beta-proteins of the T-cell receptor. In addition, a third receptor-like gene, the gamma-chain gene, has been identified, which has many structural and sequence characteristics in common with the alpha- and beta-chain genes. The role of the gamma-chain gene in T-cell development is unknown. We have reported recently that the beta-chain genes are transcriptionally turned on in the thymus at about day 17 of fetal development. Here we report that the alpha-chain also is transcriptionally activated during this time, but that the gamma-chain gene is active in the thymus at day 14, reaches a peak steady-state level at day 15 and rapidly declines thereafter. If the gamma-chain gene has a functional role, it would seem to be involved very early in T-cell development, before the mature T-cell receptor is expressed.