How polymorphic are class II loci of the mouse H-2 complex?

Area of Science:

• Immunogenetics
• Molecular Evolution
• Comparative Genomics

Background:

• The mouse major histocompatibility complex (MHC) class II region contains genes crucial for immune responses.
• Understanding the polymorphism of these genes is vital for studying immune diversity and evolution.

Purpose of the Study:

• To investigate the extent and distribution of restriction fragment length polymorphism (RFLP) in mouse MHC class II genes.
• To compare the polymorphism levels across different class II loci (A alpha, A beta, E alpha, E beta) and evaluate existing hypotheses on MHC organization.

Main Methods:

• DNA isolation from 75 mouse strains with diverse H-2 haplotypes.
• Restriction endonuclease digestion (Bst EII, Eco RI, Bam HI) of DNA.
• Southern blotting and hybridization with probes for MHC class II genes.
• Determination of RFLP at A alpha, A beta, E alpha, and E beta loci.

Main Results:

• Significant variation in polymorphism was observed: A beta > E beta > E alpha = A alpha.
• The A beta and E beta loci exhibited substantially higher polymorphism than A alpha and E alpha.
• Findings contradict the hypothesis of a centromeric/telomeric polymorphic division within the class II region.
• Polymorphism levels appear intrinsic to the loci themselves, exceeding that of other chromosome 17 genes like the alpha 4-globin pseudogene.

Conclusions:

• The degree of polymorphism in MHC class II genes is locus-specific, not determined by regional location.
• High polymorphism in A beta and E beta suggests rapid evolution and potential for fine-scale population differentiation.
• Linkage disequilibrium exists among A alpha, A beta, and E beta, while E alpha shows independent variation.