Evidence for recombinatorial hot spots at the T cell receptor J alpha locus

The complex genomic organization of the murine T cell receptor (TcR) delta-alpha region has hindered detailed studies of alpha gene rearrangement and J alpha gene usage in individual differentiating T cell precursors. We have isolated a novel set of J alpha probes which, in combination with a few restriction enzyme digests, enable a reliable, simple and nearly complete analysis and location of any rearrangement at the J alpha locus by conventional Southern blotting. The probes were used to analyze TcR alpha gene rearrangements in T cell hybridomas derived from an in vitro culture system that supports T cell differentiation of bone marrow cells. Our results indicate that J alpha genes are unequally accessible for rearrangement and two hot spots for rearrangement could be demonstrated. In addition, only a restricted set of J alpha genes was rearranged in each culture indicating that the slightly variable composition of factors can influence the recombinatorial accessibility of J alpha genes. The hot spots for rearrangement were not only limited to T cells differentiating in vitro but could also be demonstrated among functional T cell clones based on the published sequence information from isolated TcR alpha gene rearrangements. The demonstration and the location of the hot spots for rearrangement in the T cell differentiation culture system opens up the possibility to study factors and mechanisms that regulate recombinatorial accessibility of TcR alpha genes.