Organisation of the Hb 1 genes of the Antarctic skate Bathyraja eatonii: New insights into the evolution of globin genes

An extensive investigation of the organisation of globin genes has greatly contributed to the understanding of universal mechanisms of gene evolution and expression. Cartilaginous fish are the first organisms that have evolved the tetrameric form of hemoglobin (Hb). So far, there has been absolute lack of data about globin genes in chondrichthyans. Bathyraja is the dominant rajid south of 60 degrees S. In the framework of the investigations on globin genes of Antarctic red-blooded and Hb-less fish we obtained the cloning of the alpha- and beta-globin cDNAs of the main Hb (Hb 1) of the skate Bathyraja eatonii. Then, a genomic fragment of 6.2 kb was isolated where the Hb 1 alpha and beta genes are linked in a tail-to-head (3' to 5') orientation. The beta-globin gene promoter region and the chromosomal organisation of the Hb 1 genes of B. eatonii have been compared to their homologues in other vertebrates. The finding of a tail-to-head linkage of the Hb 1 alpha- and beta-globin genes in B. eatonii is the first characterisation of the organisation of globin genes in chondrichthyes; such finding offers a novel contribution to the understanding of the evolution of this class of genes. Moreover, the characterisation of chondrichthyan genes is very important for gaining insight into the ancestral state of vertebrate genomes.