Restriction of endogenous T cell antigen receptor beta rearrangements to Vbeta14 through selective recombination signal sequence modifications.

ABSTRACT

T cell antigen receptor (TCR)beta V(D)J variable region exon assembly is ordered, with Dbeta to Jbeta rearrangements occurring before joining of Vbetas to a DJbeta 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. Vbeta segments have 23-RSs and Jbeta segments 12-RSs, which based on the 12/23 rule should allow direct joining. However, Vbeta segments rearrange only to DJbeta complexes and not Jbeta segments, because of restrictions beyond 12/23 (B12/23) that make the Vbeta23-RS incompatible with the Jbeta12-RS. To determine whether direct Vbeta to Jbeta joining occurs if flanking RSs are B12/23 compatible, we generated mice whose lymphocytes contained replacement of the Vbeta1412-RS with the 3'Dbeta112-RS on a TCRbeta allele lacking Dbeta segments (the Jbeta1(M6) allele). Mice heterozygous for the Jbeta1(M6) allele had dramatically increased Vbeta14(+) thymocyte and T cell numbers and decreased numbers of cells expressing other Vbetas. This altered Vbeta repertoire resulted from direct Vbeta14 to Jbeta1 rearrangements on the Jbeta1(M6) allele. Mice harboring lymphocytes homozygous for Jbeta1(M6) allele developed normal thymocyte and T cell numbers with all expressing Vbeta14. Our findings show that selective RS modifications enforce rearrangement of a specific Vbeta gene segment and demonstrate the importance of B12/23 mechanisms for ensuring generation of diverse TCRbeta repertoires.