title: Gene turnover in the avian globin gene families and evolutionary changes in hemoglobin isoform expression.
abstract: The apparent stasis in the evolution of avian chromosomes suggests that birds may have experienced relatively low rates of gene gain and loss in multigene families. To investigate this possibility and to explore the phenotypic consequences of variation in gene copy number, we examined evolutionary changes in the families of genes that encode the α- and β-type subunits of hemoglobin (Hb), the tetrameric α2β2 protein responsible for blood-O2 transport. A comparative genomic analysis of 52 bird species revealed that the size and membership composition of the α- and β-globin gene families have remained remarkably constant during approximately 100 My of avian evolution. Most interspecific variation in gene content is attributable to multiple independent inactivations of the α(D)-globin gene, which encodes the α-chain subunit of a functionally distinct Hb isoform (HbD) that is expressed in both embryonic and definitive erythrocytes. Due to consistent differences in O2-binding properties between HbD and the major adult-expressed Hb isoform, HbA (which incorporates products of the α(A)-globin gene), recurrent losses of α(D)-globin contribute to among-species variation in blood-O2 affinity. Analysis of HbA/HbD expression levels in the red blood cells of 122 bird species revealed high variability among lineages and strong phylogenetic signal. In comparison with the homologous gene clusters in mammals, the low retention rate for lineage-specific gene duplicates in the avian globin gene clusters suggests that the developmental regulation of Hb synthesis in birds may be more highly conserved, with orthologous genes having similar stage-specific expression profiles and similar functional properties in disparate taxa.
authors.affiliation: Instituto de Ciencias Ambientales y Evolutivas, Facultad de Ciencias, Universidad Austral de Chile, Valdivia, Chile.
authors.forename: Juan C
authors.initials: JC
authors.lastname: Opazo
authors.affiliation: Department of Biochemistry, Molecular Biology, Entomology, and Plant Pathology, Mississippi State University Institute for Genomics, Biocomputing, and Biotechnology, Mississippi State University.
authors.forename: Federico G
authors.initials: FG
authors.lastname: Hoffmann
authors.affiliation: School of Biological Sciences, University of Nebraska, Lincoln.
authors.forename: Chandrasekhar
authors.initials: C
authors.lastname: Natarajan
authors.affiliation: Department of Biology, University of New Mexico Museum of Southwestern Biology, University of New Mexico.
authors.forename: Christopher C
authors.initials: CC
authors.lastname: Witt
authors.affiliation: Institute of Integrative Biology, University of Liverpool, Liverpool, United Kingdom.
authors.forename: Michael
authors.initials: M
authors.lastname: Berenbrink
authors.affiliation: School of Biological Sciences, University of Nebraska, Lincoln jstorz2@unl.edu.
authors.forename: Jay F
authors.initials: JF
authors.lastname: Storz
mesh_terms: D000818:Animals; D030161:Avian Proteins / Q000235:genetics*; D001717:Birds / Q000235:genetics*; D019143:Evolution, Molecular; D018628:Gene Dosage; D023281:Genomics; D005810:Multigene Family; D010802:Phylogeny; D020033:Protein Isoforms / Q000235:genetics; D055542:alpha-Globins / Q000235:genetics*; D055544:beta-Globins / Q000235:genetics*
chemical_list: D030161:Avian Proteins; D020033:Protein Isoforms; D055542:alpha-Globins; D055544:beta-Globins
keywords: avian genomics; gene deletion; gene duplication; gene family evolution; hemoglobin; protein evolution