Rearrangement and Selection in the Developing Vκ Repertoire of the Mouse: An Analysis of the Usage of Two Vκ Gene Segments

Abstract

Detailed analysis of the rearrangement and expression of two mouse Vκ genes has been used to examine B cell repertoire development. The Vκ1-A gene is used by a large proportion (9.6%) of splenic B cells in the adult primary repertoire, whereas the Vκ22 gene is used at a much lower frequency (0.16%). Consistent with these results, quantitative PCR (Q-PCR) assays revealed that the number of splenic B cells with rearranged Vκ1-A genes is much greater than the number with rearranged Vκ22 genes. Q-PCR was also performed on both normal bone marrow pre-B cells and transformed pre-B cells induced to rearrange their κ loci at high frequency. In contrast to splenic B cell rearrangements, the numbers of Vκ1-A and Vκ22 rearrangements in pre-B cells differ by only two- or threefold, suggesting that the intrinsic rearrangement frequencies of these two Vκ genes are not significantly different. Further evidence of disproportionate selection was obtained by comparing the percentages of productive rearrangements amplified from genomic splenic DNA. Sequence analysis showed 84% (37 of 44) of the Vκ1-A rearrangements but only 57% (29 of 51) of the Vκ22 rearrangements to be in-frame. Together these results suggest that B cells expressing Vκ1-A-encoded light chains are preferentially selected either in the periphery or in the transition from pre-B to B cell. Sequence data also reveal a surprisingly restricted diversity of VJ junctions, apparently due to biases introduced by the rearrangement mechanism.