MOLECULAR EVOLUTION OF GROWTH HORMONE IN CETARTIODACTYLA
Z Maniou, OC Wallis, AJ Sami & M Wallis
The sequence of pituitary growth hormone (GH) is generally strongly conserved in mammals, but short bursts of rapid change during the evolution of primates and artiodactyls have led to marked differences in primary structure and biological specificity in human and ruminant GHs. Recent molecular studies have shown that Cetacea are nested within Artiodactyla, and the combined grouping (Artiodactyla and Cetacea) has been termed the Cetartiodactyla. To explore further GH evolution in this group we have cloned and characterised the GH gene from several cetartiodactyl species including the common dolphin (Delphinus delphi) and the camel (Camelus dromedarius). Genomic DNA was isolated from liver, and the GH genes were amplified using PCR and primers based on known sequences from artiodactyl GH genes. The PCR products were purified, cloned and sequenced. The dolphin and camel GH genes extend over about 1900 bp and, like other mammalian GH genes, are split into 5 exons and 4 introns. In each case, the derived amino acid sequence of dolphin and camel pre-GH comprises a 26-residue signal peptide and a 190 residue mature GH sequence. The amino acid sequences of dolphin and camel GHs differ at four residues; each differs from pig GH at only two residues and from bovine GH at 16 (dolphin) or 18 (camel) residues. The data accord with the idea that Cetacea should be nested within Artiodactyla and indicate that the episode of rapid GH evolution in the line leading to ruminants occurred after divergence of camelids and cetaceans.