Evolutionary expansion of Mhc class I loci in the mole-rat, Spalax ehrenbergi

A cosmid genomic library was prepared from a single individual of the rodent Spalax ehrenbergi, the mole rat, captured in Israel. The library was screened with a mouse probe hybridizing with all mouse class I major-histocompatibility-complex (Mhc) genes; the cross-hybridizing clones were isolated; and their restriction maps were prepared using five enzymes. A total of 93 class I-bearing clones could be identified in the library. Forty-five of these clones showed partial overlaps and could be arranged into 14 clusters. Eleven of these clusters could be shown to contain two class I genes each; the remaining clusters, as well as most of the non-overlapping clones, each contained one class I gene. After the elimination of clones with possible cloning artifacts and of clones that may carry allelic forms of a given gene in the heterozygous animal, the total number of class I loci identified in Spalax is approximately 65. The high number of loci probably arose from the duplication of either the entire class I set or the different class I families. The high number of gene copies might represent a means of selecting different functional genes from the family in different mammalian orders. Three of the approximately 65 Spalax class I genes cross-hybridize with a probe specific for the mouse K, D, and L genes; two of these genes are in the same cluster. These three elements might possibly be the functional class I genes of the mole rat.