Untitled

Abstract

Growth hormone, prolactin, the fish hormone, somatolactin, and related mammalian placental hormones, including placental lactogen, form a family of polypeptide hormones that share a common tertiary structure. They produce their biological effects by interacting with and dimerizing specific single transmembrane-domain receptors. The receptors belong to a superfamily of cytokine receptors with no intrinsic tyrosine kinase, which use the Jak-Stat cascade as a major signalling pathway. Hormones and receptors are thought to have arisen as a result of gene duplication and subsequent divergence early in vertebrate evolution. Mammalian growth hormone and prolactin show a slow basal evolutionary rate of change, but with episodes of accelerated evolution. These occurred for growth hormone during the evolution of the primates and artiodactyls and for prolactin in lineages leading to rodents, elephants, ruminants, and man. Placental lactogen has probably evolved independently on three occasions, from prolactin in rodents and ruminants and from growth hormone in man. Receptor sequences also show variable rates of evolution, corresponding partly, but not completely, with changes in the ligand. A principal biological role of growth hormone, the control of postnatal growth, has remained quite consistent throughout vertebrate evolution and is largely mediated by insulin-like growth factors. Prolactin has many and diverse roles. In relation to lactation, the relative roles of growth hormone and prolactin vary between species. Correlation between the molecular and functional evolution of these hormones is very incomplete, and it is likely that many important functional adaptations involved changes in regulatory elements, for example, altering tissue of origin or posttranscriptional processing, rather than change of the structures of the proteins themselves.

Evolution of the mammalian placenta revealed by phylogenetic analysis

“…Human placental lactogens are trophoblast-secreted (27) members of the growth hormone family (28) that play a role in inducing the diabetogenetic effect (29-31) of pregnancy (26,32,33). Placental lactogens have evolved independently at least three times during mammalian evolution (34,35). The increased concentration of placental lactogens in the maternal circulation results in the increased fetal utilization of maternal resources, and therefore maternal-fetal conflict can occur (36,37).…”

Molecular anatomy of the cytoplasmic domain of bovine growth hormone receptor, a quantitative trait locus

“…The intracellular signalling domain (target of this study) shows a relatively high but constant evolutionary rate, with acceleration only in rodents. Thus, in primates and artiodactyls, the episodes of rapid change in GH are matched by corresponding episodes in the extracellular (GH-binding) domain of GHR, which would accord with their being driven by adaptive changes (Liu et al 2001;Forsyth & Wallis 2002). Although, unlike the GH, the intracellular domain of GHR does not seem to be driven by positive selection in ruminants, in cattle it harbours interesting polymorphism.…”

Cloning and expression of a unique short form of the porcine prolactin receptor

“…The PRL gene for primates, rodents, and ruminants/pigs diverged from each other at least 75 million years ago, while the pig PRL gene diverged from the ruminant PRL gene only 55 million years ago (Wallis 2000). The divergence in the PRLR is presumed to have occurred at the same time (Forsyth & Wallis 2002), given the co-evolution of PRL with its receptor (Li et al 2005). In fact, the phylogenetic tree comparing full-length PRLR-LF from birds, mammals, marsupials, and fish (Fig.…”