Major Histocompatibility Complex Gene Organization in the Mole Rat Spalax ehrenbergi: Evidence for Transfer of Function between Class II Genes

A genomic DNA library prepared from the kidney of the mole rat Spalax ehrenbergi was screened with mouse probes representing major histocompatibility complex genes that encode α and β polypeptide chains of class II molecules (α and β genes). Restriction maps were constructed for the cross-hybridizing clones, and the class II genes borne by these clones were identified. By this procedure, five main regions containing class II genes were established. One region contained four genes and two gene fragments, the second region contained two genes, the third region contained one gene and one gene fragment, and the remaining two regions contained one gene each. Altogether, six β genes, two α genes, and three α -gene fragments were identified. Two of the genes (one α and one β ) were established as belonging to the DQ subclass, and all other genes were found to be members of the DP subclass. (Subclass designations are based on the human HLA class II genes.) No genes belonging to the DR and DO (DZ) subclasses were found in the library. The absence of DR genes in S. ehrenbergi was also indicated when other experimental methods were used. At least some of the DP loci are polymorphic and most likely also functional. Thus, in the evolution of the mole rat, the DR (and probably also the DO) loci have been deleted and their function(s) has been taken over by the DP loci, which have expanded to a great extent. These findings argue for functional interchangeability of the individual subclasses of class II loci.