Globin genes in Antarctic fish: Trematomus newnesi Hb 1 system; Hb loss in Channichthyids

The study of globin genes has greatly contributed to the understanding of universal mechanisms of gene evolution and of gene expression regulation. In Notothenioidei, the dominant suborder of Antarctic fish, the investigation of the organization of globin genes is particularly interesting in order to characterize the evolutionary mechanisms which led to the hemoglobin loss of the family Channichthyidae. The Antarctic fish Trematomus newnesi has an oxygen transport system with unique characteristics among notothenioids. The cloning and sequence analysis of the ?- and ?-globin cDNAs of the major hemoglobin of T. newnesi, with the determination of the linkage of the relative genes, is herewith reported. The orientation of T. newnesi Hb 1 ?- and ?-globin genes was head-to-head, corresponding to the classical organization of fish globin genes. Seven of the eight notothenioid families are red-blooded but have reduced erythrocyte number and hemoglobin multiplicity; all 16 species of the eighth family (Channichthyidae) are completely devoid of hemoglobin (white-blooded icefish) and represent a novel and unique phenotype in the evolutionary history of fish and vertebrates. Therefore, studies have aimed at evaluating the pathway of genomic change and the mechanisms that have led to the loss of hemoglobin expression by the white-blooded icefish. Adult and embryonic/juvenile gene complexes from a closely related, red-blooded notothenioid species were isolated and characterized. The results indicate that in channichthyids the adult ?-globin gene is absent and that the inability to express hemoglobin in these fishes might have arisen from a large-scale deletional event.