Characterization and genotyping of the DRB1 gene of the major histocompatibility complex (MHC) in the Marmota monax, animal model of hepatitis B

• We have characterized the DRB1 exon 2 region in Marmota monax.
• The detected 15 alleles were classified in two clusters named DRB1-A and DRB1-B.
• Positive selection acting in both clusters was observed.
• Low heterozygosity was obtained due to the elevated rate of null alleles.
• A microsatellite that could allow the semiautomatic sequencing was identified.

The major histocompatibility complex (MHC)-containing genes are among the most polymorphic in vertebrates. MHC genes code for proteins that are critical in the immune system response. In this study, the polymorphism of the second exon of the MHC class II DRB gene was characterized in the Eastern woodchuck (Marmota monax). Woodchucks chronically infected with the woodchuck hepatitis virus (WHV) represent the best available animal model for the study of chronic hepatitis B infection in humans. In the genotyped animals we found fifteen alleles, which were expressed in two independent loci and that were named DRB1A and DRB1B in this work. The 15 alleles investigated showed an elevated divergence. A significant excess of non-synonymous substitutions was detected, which could indicate that a historical positive selection is acting in the woodchuck DRB1 genes. This hypothesis was confirmed in our study by the high variability in or near the antigen binding sites (ABS) and by the results obtained in sequence variability analyses. This analysis identified the presence of a microsatellite sequence that is located at the start of the second intron, which could further allow the development of a fast and cheap semiautomatic sequencing method.