The Rise And Fall Of Globins In The Amphibia

The globin gene repertoire of gnathostome vertebrates is dictated by differential retention and loss of nine paralogous genes: androglobin, neuroglobin, globin X, cytoglobin, globin Y, myoglobin, globin E, and the alpha- and beta-globins. We report the globin gene repertoire of three orders of modern amphibians: Anura, Caudata, and Gymnophiona. Combining phylogenetic and conserved synteny analysis, we show that myoglobin and globin E were lost only in the Batrachia clade, but retained in Gymnophiona. The major amphibian groups also retained different paralogous copies of globin X. None of the amphibian presented alpha(D)-globin gene. Nevertheless, two clades of beta-globins are present in all amphibians, indicating that the amphibian ancestor possessed two paralogous proto beta-globins. We also show that orthologs of the gene coding for the monomeric hemoglobin found in the heart of Rana catesbeiana are present in Neobatrachia and Pelobatoidea species we analyzed. We suggest that these genes might perform myoglobinand globin E-related functions. We conclude that the repertoire of globin genes in amphibians is dictated by both retention and loss of the paralogous genes cited above and the rise of a new globin gene through co-option of an alpha-globin, possibly facilitated by a prior event of transposition.