Supertyping of MHC IA in Non-Model Asian Anurans

Abstract

The major histocompatibility complex (MHC) plays a central role in vertebrate disease resistance. However, MHC genetic organization varies widely among vertebrates, which may have implications for pathogen resistance conferred by the MHC. Amphibians, as the first terrestrial vertebrates, offer a window into early MHC evolution. I characterized, for the first time, the MHC class I of two indigenous Korean anurans. Primers designed in conserved regions of exons 1 and 4 allowed for full characterization of the peptide binding region (exons 2 and 3). In both the Asiatic toad (Bufo gargarizans) and the Japanese tree frog (Hyla japonica), I found at least four transcribed classical MHC class I (MHC IA) loci, the highest number confirmed in any anuran to date. Furthermore, MHC IA transcripts were identified not only in terrestrial adults but also in aquatic larvae of both species. In MHC IA phylogenetic trees, B. gargarizans and H. japonica clustered in the superfamily Nobleobatrachia, similar to trees constructed with neutral genetic markers. Finally, by employing a supertyping methodology, six supertypes were identified, three of which were shared by these two species in South Korea. Possibly these shared supertypes reflect evolved resistance to common pathogens in the local environment. Results reveal substantial variation in the number of MHC IA loci in anurans. They also suggest that certain supertypes have particular physiochemical properties that may confer pathogen resistance.