Molecular evolution of growth hormone (GH) in cetartiodactyla: Cloning andcharacterization of the gene encoding GH from a primitive ruminant, the chevrotain (Tragulus javanicus)

In mammals the sequence of pituitary growth hormone (GH) is generally stron gly conserved, indicating a slow basal rate of molecular evolution. However , on two occasions, during the evolution of primates and that of cetartioda ctyls, the rate of evolution has increased dramatically (25 to 50-fold) so that the sequences of human and ruminant GHs differ markedly from those of other mammalian GHs. To define further the burst of CH evolution that occur red in cetartiodactyls, the GH gene of the chevrotain (Tragulus javanicus) has been cloned and characterized by use of genomic DNA and a polymerase ch ain reaction technique. Two very similar gene sequences, which probably ref lect allelic variation, were isolated. The deduced sequence for the mature chevrotain GH differs from that of the bovine or red deer GH at only two to three residues, and phylogenetic analysis shows that the burst of rapid ev olution of GH that occurred in the Cetartiodactyla must have been completed before the divergence of the Tragulidae and the advanced ruminants (Pecora ). The rate of evolution during this burst must therefore have been greater than previously estimated. In other aspects (including signal sequence, 5 ' upstream sequence, and synonymous substitutions in the coding sequence), the chevrotain GH gene differs considerably from the GH genes of other rumi nants and here there is no evidence for the period of accelerated evolution that is seen for GH itself. (C) 2001 Academic Press.