title: Support for the minimal essential MHC hypothesis: a parrot with a single, highly polymorphic MHC class II B gene.
abstract: We characterized the MHC class II B gene in the green-rumped parrotlet, Forpus passerinus. Three approaches were used: polymerase chain reaction amplification using primers complementary to conserved regions of exon 2, sequencing clones from a genomic library, and amplification of exon 2 using species-specific primers. All three methods indicate that there is only a single class II B locus in this species and no pseudogenes. We suggest that this is the ancestral state for birds. The gene is highly polymorphic; 33 alleles were found in a sample of 25 individuals. Variation in exon 2 is concentrated in the peptide binding residues which show a significant excess of non-synonymous substitutions consistent with the operation of selection in maintaining this extraordinary polymorphism. Genomic clones show that major histocompatibility complex (MHC) gene organization is different from that of chickens; the class II A locus is close to II B. These data provide support for the hypothesis that the bird MHC constitutes a "minimal essential MHC" for responding to infectious disease.
authors.affiliation: Department of Biological Sciences, Florida Atlantic University, 2912 College Ave., Davie, FL 33314, USA. colin.hughes@fau.edu
authors.forename: Colin R
authors.initials: CR
authors.lastname: Hughes
authors.forename: Shana
authors.initials: S
authors.lastname: Miles
authors.forename: Jaclyn M
authors.initials: JM
authors.lastname: Walbroehl
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000949:Histocompatibility Antigens Class II / Q000235:genetics*; D008957:Models, Genetic; D008969:Molecular Sequence Data; D010311:Parrots / Q000235:genetics*; D011110:Polymorphism, Genetic; D013045:Species Specificity
chemical_list: D000949:Histocompatibility Antigens Class II