Restriction of endogenous T cell antigen receptor β rearrangements to Vβ14 through selective recombination signal sequence modifications

T cell antigen receptor (TCR)beta V(D)J variable region exon assembly is ordered, with D beta to J beta rearrangements occurring before joining of V beta s to a DJ beta complex. Germ-line V(D)J segments are flanked by recombination signal (RS) sequences, which consist of heptamers and nonamers separated by a spacer of 12 (12-RS) or 23 (23-RS) bp. V(D)J recombination is restricted by the 12/23 rule; joining occurs only between gene segments flanked by 12-RSs and 23-RSs. V beta segments have 23-RSs and J beta segments 12-RSs, which based on the 12/23 rule should allow direct joining. However, V beta segments rearrange only to DJ beta complexes and not JP segments, because of restrictions beyond 12/23 (B12/23) that make the V beta 23-RS incompatible with the J beta 12-IRS. To determine whether direct V beta to JP joining occurs if flanking RSs are B12/23 compatible, we generated mice whose lymphocytes contained replacement of the V beta 1412-RS with the 3'D beta 112-RS on a TCR beta allele lacking D beta segments (the J beta 1(M6) allele). Mice heterozygous for the J beta 1(M6) allele had dramatically increased VP14+ thymocyte and T cell numbers and decreased numbers of cells expressing other V beta s. This altered V beta repertoire resulted from direct V beta 14 to J beta 1 rearrangements on the J beta 1(M6) allele. Mice harboring lymphocytes homozygous for J beta 1(m6) allele developed normal thymocyte and T cell numbers with all expressing V beta 14. Our findings show that selective RS modifications enforce rearrangement of a specific V beta gene segment and demonstrate the importance of B12/23 mechanisms for ensuring generation of diverse B12/13 repertoires.