Excision products of the T cell receptor gene support a progressive rearrangement model of the α/δ locus

Abstract

We have cloned extrachromosomal circular DNAs containing T cell receptor (TCR) δ gene segments in adult mouse thymocytes and splenocytes. We find that the frequency of circular DNA clones carrying germline δ sequences is lower than that of Jα probe-positive clones, possibly related to increasing 5' distance from the most upstream Jα segment. This suggests that the TCR α/δ locus is successively rearranged from within and that the δ-containing excision products are progressively diluted out by the subsequent cell division which includes further α gene rearrangements. In addition, examination of δ gene excision products revealed newly identified Vδ subfamilies, the reciprocal joining of two Dδ elements, Jδ2 usage in thymocytes and novel sequences homologous to the human δ-gene deleting elements.