Characterization of a V kappa family in Mus musculus castaneus: expansion at the subset level.

We have examined the same kappa chain variable (V kappa) region family in several mouse species in order to observe short-term, incremental change at immunoglobulin (Ig) multigene loci. In the present study, the Igk-V24 family has been characterized in a Mus m. castaneus colony derived from individuals originating in Thailand and compared to the same family in Mus m. domesticus (BALB/c) and Mus pahari, representing about 1-2 and about 5-9 million years of evolution, respectively. Southern hybridization of genomic DNA with a probe encoding the prototype Igk-V24 coding region reveals restriction fragment patterns indicative of two distinct M. m. castaneus haplotypes. These haplotypes appear to result from an unequal recombination between similar gene arrays, as their restriction patterns are unique but contain many common fragments. The complexity of these patterns indicates a marked expansion in the Igk-V24 family of M. m. castaneus relative to BALB/c and M. pahari. Additional analyses using probes specific for individual subsets demonstrate that the expansion is not general throughout the entire family, but is restricted to particular subsets and therefore to relatively short chromosomal segments. One subset alone accounts for most of the expansion and comprises over 40% of the entire M. m. castaneus family. The wide range of Igk-V24 family complexity seen among M. m. castaneus, M. m. domesticus, and M. pahari, as well as among the different M. m. castaneus family subsets, suggests a model of random evolution in V kappa family copy number rather than one which is selective.