Asymmetric contribution to Ig repertoire diversity by V kappa exons: differences in the utilization of V kappa 10 exons.

The mouse has approximately 140 germline V kappa genes, and functional V kappa exons are expressed at roughly equivalent levels in the preimmune repertoire. We have examined the expression of individual members of the V kappa 10 family. V kappa 10A and V kappa 10B genes have been utilized in numerous hybridomas and myelomas, while V kappa 10C has not. In this study, we have cloned the V kappa 10C gene and shown that it is structurally functional, has the expected promoter elements and recombination signal sequences, and that it is capable of recombination. V kappa 10C mRNA, however, is present at levels at least 1000-fold lower than V kappa 10A and V kappa 10B in adult spleens. While there are no sequence differences in the octamer or TATA box between V kappa 10C and V kappa 10A, there are three nucleotide changes in the promoter region. These promoters equally drive the expression of a reporter gene in B cells or plasma cells, but the V kappa 10A promoter is able to drive expression in pre-B cell lines significantly better than the V kappa 10C promoter (p < 0.05). V kappa 10C rearrangements can be detected in bone marrow and splenic DNA. Therefore, the lack of V kappa 10C expression may reflect the inability of V kappa 10C-rearranged cells to undergo positive or negative selection. Our results suggest that the available Ab repertoire is shaped not only by the number of structurally functional genes, but also by the ability of assembled genes to be expressed at critical points during B cell maturation.