V-D-J rearrangements at the T cell receptor σ locus in mouse thymocytes of the αβ lineage

AbstractThe T cell receptor (TCR) σ locus lies within the TCR α locus and is excised from the chromosome by Vα-Jα rearrangement. We show here that σ sequences persist in a large fraction of the DNA from mature CD4+CD8−αβ+ mouse thymocytes. Virtually all σ loci in these cells are rearranged and present in extrachromosomal DNA. In immature αβ lineage thymocytes (CD3−/loCD4+CD8+) and in CD4+CDS−αβ+ thymocytes expressing a transgene-encoded αβ receptor, rearranged σ genes are present both in chromosomal and extrachromosomal DNA. Thus, contrary to earlier proposals, commitment to the αβ lineage does not require recombinational silencing of the σ locus or its deletion by a site-specific mechanism prior to Vα-Jα rearrangement