Evolutionary origin and divergence of the growth hormone receptor family: insight from studies on sea lamprey.

Sea lamprey, one of the oldest extant lineages of vertebrates, Agnatha, was used to clarify the evolutionary origin and divergence of the growth hormone receptor (GHR) family. A single full-length cDNA encoding a protein that shares amino acid identity with GHRs and prolactin receptors (PRLRs) previously characterized from teleost fish was identified. Expression of the GHR/PRLR-like transcript was widespread among tissues, including brain, pituitary, heart, liver, and skeletal muscle, which is consistent with the broad physiological roles of GH-family peptides. Phylogenetic analysis suggests that the lamprey possess an ancestral gene encoding a common GHR/PRLR that diverged to give rise to distinct GHRs and PRLRs later in the course of vertebrate evolution. After the divergence of the Actinopterygian and Sarcopterygian lineages, the GHR gene was duplicated in the Actinopterygian lineage during the fish-specific genome duplication event giving rise to two GHRs in teleosts, type 1 GHR and type 2 GHR. A single GHR gene orthologous to the teleost type 1 GHR persisted in the Sarcopterygian lineage, including the common ancestor of tetrapods. Within the teleosts, several subsequent independent duplication events occurred that led to several GHR subtypes. A revised nomenclature for vertebrate GHRs is proposed that represents the evolutionary history of the receptor family. Structural features of the receptor influence ligand binding, receptor dimerization, linkage to signal effector pathways, and, ultimately, hormone function.

Rapid evolution of osmoregulatory function by modification of gene transcription in steelhead trout.

Populations experiencing sudden environmental change must be capable of rapidly evolving to survive. Here we explore changes in gene transcription as a mechanism for rapid adaptation at four osmoregulatory genes (CFTR I, NaK ATPase1αa, NaK ATPase1αb and GHRII) in anadromous steelhead trout versus a derived land-locked population after 14 generations. Transcription was measured before and after a 24-h saltwater challenge in pure and reciprocal hybrid offspring of fish from both populations reared in a common environment for two generations. Significant differences between the landlocked and migratory populations were observed, particularly in fresh water at the NaK ATPase1αa and GHRII genes, indicating rapid evolutionary change, possibly associated with reduced energy expenditure in the landlocked lake system. Phenotypic divergence analysis (Q (ST)) shows that the observed transcriptional differences deviate from neutral expectations. Some reciprocal crosses exhibited anomalous transcription consistent with sex-linked epistatic or genetic imprinting effects. Our results highlight unpredictable phenotypic outcomes of hybridization among locally adapted populations and the need to exercise caution when interbreeding populations for conservation purposes.

Indication of different lactogen and somatogen binding sites in the human growth hormone molecule as probed with monoclonal antibodies.

The relationship between the structure of human growth hormone (hGH) and the hormone-receptor interaction has been investigated using as probes monoclonal antibodies (Mabs) to hGH of defined epitope specificity profile. Seven high affinity Mabs were studied for their ability (i) to inhibit the binding of 125I-hGH to Nb2-SP rat lymphoma cells and to IM-9 human lymphocytes possessing lactogen and somatogen type receptors, respectively; and (ii) to interfere with the hormone (hGH or Met8Leu hGH)-induced proliferation in Nb2-11C lymphoma cells. The ability of these Mabs to inhibit the 125I-hGH binding and the hormone-induced proliferation in Nb2-11C cells was negatively correlated with the ability of these Mabs to cross-react with met14 hGH. Furthermore, Mabs Nos. 3 and 7, which cross-reacted minimally (0.2-0.4%) with Met8Leu hGH, were unable to interfere with the mitogenic activity of Met8Leu hGH in Nb2-11C cells. These results indicate that the first 13 amino acids of the N-terminal region of hGH are necessary for its lactogen activity. The inhibition of 125I-hGH binding to IM-9 cells by these Mabs was similar to those observed in Nb2-SP cells, except for Mabs Nos. 19 and 1. These Mabs inhibited more strongly the binding of 125I-hGH to IM-9 than to Nb2 cells and recognized antigenic epitopes close to the C-terminal part of the molecule. These results suggest that the somatogen receptor binding site of hGH may be located on two sites, one at the N-terminal and the other one close to the C-terminal, while the lactogen receptor is mainly confined to the N-terminal part.

Differences in both glycosylation and binding properties between rat and mouse liver prolactin receptors.

To investigate whether glycanic chains of prolactin receptors (PRL-R) play a role in hormone binding activity, comparison was made of rat and mouse liver solubilized receptors with respect to both their affinity for the hormone and their glycosylation properties. As compared with rat receptors, mouse receptors exhibited a 2-fold higher affinity for human growth hormone (hGH), the hormone being bound by both tissues with a lactogenic specificity. Along with this increased affinity, mouse receptors had a 2 lower M(r) relative to rat receptors (62 kDa versus 64 kDa as measured on hGH cross-linked receptors). These differences could be ascribed to different glycosylation properties of the receptors from the two species, as supported by the followings. 1) After treatment with endoglycosidase F (endo F), rat and mouse PRL-R no longer exhibited any difference in their M(r) (54 kDa for both cross-linked receptors). 2) Neuraminidase treatment increased by 37% the binding of hGH to mouse receptors, but was ineffective on the hormone-binding to rat receptors. Conversely, wheat germ agglutinin (WGA), another sialic acid specific probe, decreased hGH binding to rat receptors by 25%, but had no effect on this process for mouse ones. 3) Marked differences were observed in the recoveries of rat and mouse hormone-receptor (HR) complexes from ricin-1- (RCA1-), concanavalin A- (ConA-) and WGA-immobilized lectins. These differences were reduced (RCA1 and ConA) or abolished (WGA) after rat and mouse receptor desialylation by neuraminidase, a treatment which decreased the M(r) of both receptors by 2 kDa. Taken together, these results strongly suggest that the PRL-R from rat and mouse liver contain biantennary N-linked oligosaccharidic chains with distinct type of sialylation, which may account for their differential hormone-binding affinities.