Structure and Evolution of a New Avian MHC Class II B Gene in a Sub-Antarctic Seabird, the Thin-Billed Prion

• Main Authors: Procellariiformes Pachyptila Belcheri, Mónica C. Silva, Æ Scott, V. Edwards, M. C. Silva, S. V. Edwards
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: Antarctic; Antarc*
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.325.8992; http://www.oeb.harvard.edu/faculty/edwards/research/publications_files/silva_mhc_prion_jme09.pdf

Abstract The major histocompatibility complex encodes molecules that present foreign peptides to T cells of the immune system. The peptide binding region (PBR) of these molecules is among the most polymorphic regions found in vertebrate taxa. Genomic cloning approaches are improving our understanding of the evolution of this multigene family in nonmodel avian groups. By building a cosmid library, a new MHC class II B gene, Pabe-DAB1, was isolated and characterized at the genomic level in a sub-Antarctic seabird, the thin-billed prion (Pachyptila belcheri). Pabe-DAB1 exhibits the hallmark structural features of functional MHC class II loci. Direct sequencing of the PBR encoding exon in a panel of prions revealed significantly higher levels of genetic diversity compared to two noncoding neutral loci, with most alleles differing by at least one replacement substitution in the peptide binding codons. We estimated evolutionary dynamics for Pabe-DAB1 using a variety of Bayesian and other approaches. Evidence for balancing selection comes from a spatially variable ratio of nonsynonymous-to-synonymous substitutions (mean dN/dS = 2.87) in the PBR, with sites predicted to be functionally relevant exhibiting the highest x values. We estimate the