Identification of the transgenic integration site in 2C T cell receptor transgenic mice

2C T cell receptor (TCR) transgenic mice have been long used to study the molecular basis of TCR binding to peptide/major compatibility complexes and the cytotoxicity mechanism of cytotoxic T lymphocytes (CTLs). To study the role of variable gene promoters in allelic exclusion, we previously constructed mutant mice in which the Vβ13 promoter was deleted (P13 mice). Introduction of 2C transgene into P13 mice accelerated the onset of systemic CD8 T cell lymphoma between 14 and 27 weeks of age, although parental P13 mice appeared to be normal. This observation suggests that the lymphoma development may be linked to features of 2C transgene. To identify the integration site of 2C transgene, Southern blotting identified a 2C-specific DNA fragment by 3' region probe of 2C TCR α transgene, and digestion-circularization-polymerase chain reaction (DC-PCR) amplified the 2C-specific DNA fragment with inverse primers specific to the southern probe. Sequence analysis revealed that DC-PCR product contained the probe sequences and the junction sequences of integration site, indicating that 2C TCR α transgene is integrated into chromosome 1. Further genomic analysis revealed cytosolic phospholipase A2 group IVA (cPLA2) as the nearest gene to the integration site. cPLA2 expression was upregulated in the normal thymi and T cell lymphomas from 2C transgenic mice, although it was not altered in the lymph nodes of 2C transgenic mice. The result is the first report demonstrating the integration site of 2C TCR transgene, and will facilitate the proper use of 2C transgenic mice in studies of CTLs.

Aberrant V(D)J cleavages in T cell receptor beta enhancer- and p53-deficient lymphoma cells

Previously, we generated thymic lymphoma cell lines from EbetaR/Rp53-/- (EP) double mutant mice where the T cell receptor (TCR) beta enhancer (Ebeta) was deleted, and the p53 gene was inactivated. Here, we characterized the EP cell lines to study the roles of the Ebeta and p53 on TCRbeta rearrangements during lymphomagenesis. Recombination activation genes (RAGs) were expressed, while the TCRbeta chain was not expressed in the EP cell lines. Dbeta-Jbeta rearrangements were not detected at all, and Dbeta1 and Dbeta2 cleavages were also not detected in the EP cell lines. However, Jbeta cleavages suppressed in Ebeta mutant thymocytes were readily detected in the EP cell lines. The Jbeta cleavages appeared to be uncoupled, aberrant, RAG-dependent and Ebeta-independent and were not detected in a p53 or Ebeta single mutant background, suggesting that the Jbeta cleavages are selected in the Ebeta and p53 double mutant background. Sequence analysis showed that the cleavage occurred in the cryptic recombination signal sequences (RSSs) present throughout Jbeta gene segments. The results implicate that the uncoupled and aberrant V(D)J cleavages may contribute to double-strand break-mediated genome instability during lymphomagenesis in EP mice.