| Summary: | As the Southern Ocean cooled to -1.8°C over the past 40 million years, the teleostean clade Notothenioidei became less reliant on hemoglobin and red blood cells, a trend which culminates in the white-blooded, erythrocyte-null Antarctic icefishes. The adult alpha and beta globin genes of red-blooded notothenioids are linked in 5'-to-5' orientation such that the intergenic sequences direct divergent transcription of the loci. To gain further insight into their evolution and function, we have compared the intergenic regions of the adult alpha/beta globin gene complexes from three species of Antarctic rockcods (Nototheniidae), a basal notothenioid group, and from eight species of Antarctic dragonfishes (Bathydraconidae), the red-blooded notothenioids most closely related to the icefishes, as well as the alpha and beta globin of 13 species and 10 genera of dragonfish. The ancestral nototheniid intergene appears to be ~3 kb in length, although one species contains a duplication of ~1 kb. The bathydraconid intergenes resolve into three distinct subclasses [long (3.8 kb), intermediate (3.0 kb), and short (1.5-2.3 kb)] that correspond to the subfamilies proposed for the taxon: Gymonodraconinae, Bathydraconinae, and Cygnodraconinae. Using luciferase reporter technology, we assessed the promoter/enhancer activities of the intergenes from the rockcod Notothenia coriiceps and the dragonfishes Akarotaxis nudiceps (Bathydraconinae) and Gerlachea australis (Cygnodraconinae) in the erythropoietic microenvironment of differentiated MEL cells. We found that the N. coriiceps intergene directs high-level transcription in both orientations, the A. nudiceps intergene is active only in alpha orientation, and the short intergene of G. australis supports only weak transcription. Phylogenetic analysis indicated that dragonfish are paraphyletic. Our alpha/beta globin, and intergenic data agree with the subfamilies proposed by mitochondrial data but Cygnodraconinae and Gymnodraconinae are more closely related and Bathydraconinae should be ...
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