Sequencing and mapping hemoglobin gene clusters in the Australian model dasyurid marsupial <i>Sminthopsis macroura</i>

Abstract

Comparing globin genes and their flanking sequences across many species has allowed globin gene evolution to be reconstructed in great detail. Marsupial globin sequences have proved to be of exceptional significance. A previous finding of a β(beta)-like ω(omega) gene in the α(alpha) cluster in the tammar wallaby suggested that the α and β cluster evolved via genome duplication and loss rather than tandem duplication. To confirm and extend this important finding we isolated and sequenced BACs containing the α and β loci from the distantly related Australian marsupial Sminthopsis macroura. We report that the α gene lies in the same BAC as the β-like ω gene, implying that the α-ω juxtaposition is likely to be conserved in all marsupials. The LUC7L gene was found 3′ of the S. macroura α locus, a gene order shared with humans but not mouse, chicken or fugu. Sequencing a BAC contig that contained the S. macroura β globin and Ε globin loci showed that the globin cluster is flanked by olfactory genes, demonstrating a gene arrangement conserved for over 180 MY. Analysis of the region 5′ to the S. macroura epsilon (Ε) globin gene revealed a region similar to the eutherian LCR, containing sequences and potential transcription factor binding sites with homology to eutherian hypersensitive sites 1 to 5. FISH mapping of BACs containing S. macroura α and β globin genes located the β globin cluster on chromosome 3q and the α locus close to the centromere on 1q, resolving contradictory map locations obtained by previous radioactive in situ hybridization.

Gene duplication, genome duplication, and the functional diversification of vertebrate globins

“…In amniote vertebrates, by contrast, the α- and β-like globin genes are located on different chromosomes, reflecting the fact that the ancestral β-globin gene was transposed to a new chromosomal location in the amniote common ancestor (Hardison 2008; Patel et al 2008, 2010). Even in mammals, the ancestral linkage arrangement of the proto α- and β-globin genes is reflected by the fact that an ‘orphaned’ β-like globin gene (ω-globin) is found in association with the tandemly linked α-like globin genes in the genomes of monotremes and marsupials (De Leo et al 2005; Hoffmann et al 2008a; Opazo et al 2008a; Wheeler et al 2001, 2004). …”