Evolution of the receptors for growth hormone, prolactin, erythropoietin and thrombopoietin in relation to the vertebrate tetraploidizations

The prolactin receptor: A cross-species comparison of gene structure, transcriptional regulation, tissue-specificity, and genetic variation

The conserved and multifaceted functions of prolactin (PRL) are coordinated through varied distribution and expression of its cell-surface receptor (PRLR) across a range of tissues and physiological states. The resultant heterogeneous expression of PRLR mRNA and protein across different organs and cell types supports a wide range of PRL-regulated processes including reproduction, lactation, development, and homeostasis. Genetic variation within the PRLR gene also accounts for several phenotypes impacting agricultural production and human pathology. The goal of this review is to highlight the many elements that control differential expression of the PRLR across tissues, and the various phenotypes that exist across species due to variation in the PRLR gene.

Transcriptional regulation of esophageal, intestinal, and branchial solute transporters by salinity, growth hormone, and cortisol in Atlantic salmon

In marine habitats, Atlantic salmon (Salmo salar) imbibe seawater (SW) to replace body water that is passively lost to the ambient environment. By desalinating consumed SW, the esophagus enables solute-linked water absorption across the intestinal epithelium. The processes underlying esophageal desalination in salmon and their hormonal regulation during smoltification and following SW exposure are unresolved. To address this, we considered whether two Na+ /H+ exchangers (Nhe2 and -3) expressed in the esophagus contribute to the uptake of Na+ from lumenal SW. There were no seasonal changes in esophageal nhe2 or -3 expression during smoltification; however, nhe3 increased following 48 h of SW exposure in May. Esophageal nhe2, -3, and growth hormone receptor b1 were elevated in smolts acclimated to SW for 2.5 weeks. Treatment with cortisol stimulated branchial Na+ /K+ -ATPase (Nka) activity, and Na+ /K+ /2Cl- cotransporter 1 (nkcc1), cystic fibrosis transmembrane regulator 1 (cftr1), and nka-α1b expression. Esophageal nhe2, but not nhe3 expression, was stimulated by cortisol. In anterior intestine, cortisol stimulated nkcc2, cftr2, and nka-α1b. Our findings indicate that salinity stimulates esophageal nhe2 and -3, and that cortisol coordinates the expression of esophageal, intestinal, and branchial solute transporters to support the SW adaptability of Atlantic salmon.

Structure of the thrombopoietin-MPL receptor complex is a blueprint for biasing hematopoiesis

Thrombopoietin (THPO or TPO) is an essential cytokine for hematopoietic stem cell (HSC) maintenance and megakaryocyte differentiation. Here, we report the 3.4 Å resolution cryoelectron microscopy structure of the extracellular TPO-TPO receptor (TpoR or MPL) signaling complex, revealing the basis for homodimeric MPL activation and providing a structural rationalization for genetic loss-of-function thrombocytopenia mutations. The structure guided the engineering of TPO variants (TPOmod) with a spectrum of signaling activities, from neutral antagonists to partial- and super-agonists. Partial agonist TPOmod decoupled JAK/STAT from ERK/AKT/CREB activation, driving a bias for megakaryopoiesis and platelet production without causing significant HSC expansion in mice and showing superior maintenance of human HSCs in vitro. These data demonstrate the functional uncoupling of the two primary roles of TPO, highlighting the potential utility of TPOmod in hematology research and clinical HSC transplantation.

Prolactin and the evolution of male pregnancy

Prolactin (PRL) is a multifunctional hormone of broad physiological importance, and is involved in many aspects of fish reproduction, including the regulation of live birth (viviparity) and both male and female parental care. Previous research suggests that PRL also plays an important reproductive role in syngnathid fishes (seahorses, pipefish and seadragons), a group with a highly derived reproductive strategy, male pregnancy - how the PRL axis has come to be co-opted for male pregnancy remains unclear. We investigated the molecular evolution and expression of the genes for prolactin and its receptor (PRLR) in an evolutionarily diverse sampling of syngnathid fishes to explore how the co-option of PRL for male pregnancy has impacted its evolution, and to clarify whether the PRL axis is also involved in regulating reproductive function in species with more rudimentary forms of male pregnancy. In contrast to the majority of teleost fishes, all syngnathid fishes tested carry single copies of PRL and PRLR that cluster genetically within the PRL1 and PRLRa lineages of teleosts, respectively. PRL1 gene expression in seahorses and pipefish is restricted to the pituitary, while PRLRa is expressed in all tissues, including the brood pouch of species with both rudimentary and complex brooding structures. Pituitary PRL1 expression remains stable throughout pregnancy, but PRLRa expression is specifically upregulated in the male brood pouch during pregnancy, consistent with the higher affinity of pouch tissues for PRL hormone during embryonic incubation. Finally, immunohistochemistry of brood pouch tissues reveals that both PRL1 protein and PRLRa and Na⁺/K⁺ ATPase-positive cells line the inner pouch epithelium, suggesting that pituitary-derived PRL1 may be involved in brood pouch osmoregulation during pregnancy. Our data provide a unique molecular perspective on the evolution and expression of prolactin and its receptor during male pregnancy, and provide the foundation for further manipulative experiments exploring the role of PRL in this unique form of reproduction.

A progestin regulates the prostaglandin pathway in the neuroendocrine system in female mudskipper Boleophthalmus pectinirostris

Sex hormones regulate the reproductive cycle through brain-pituitary axis, but the molecular mechanism is still enigmatic. In the reproductive season, the mudskipper Boleophthalmus pectinirostris possesses a semilunar periodicity spawning rhythm, which coincides with the semilunar periodicity variations in 17α-hydroxyprogesterone, the precursor of 17α,20β-dihydroxy-4-pregnen-3-one (DHP), a sexual progestin in teleosts. In the present study, we investigated in vitro the brain transcriptional differences between DHP-treated tissues and control groups using RNA-seq. Differential expression analysis revealed that 2700 genes significantly differentially expressed, including 1532 up-regulated and 1168 down-regulated genes. The majority of prostaglandin pathway-related genes were dramatically up-regulated, especially the prostaglandin receptor 6 (ptger6). Tissue distribution analysis revealed that ptger6 gene was ubiquitously expressed. In situ hybridization results showed that ptger6, nuclear progestin receptor (pgr), and DHP-induced c-fos mRNA were co-expressed in the ventral telencephalic area, the ventral nucleus of ventral telencephalic area, the anterior part of parvocellular preoptic nucleus, the magnocellular part of magnocellular preoptic nucleus, the ventral zone of periventricular hypothalamus, the anterior tubercular nucleus, the periventricular nucleus of posterior tuberculum, and the torus longitudinalis. DHP significantly enhanced promoter activities of ptger6 via Pgr. Together, this study suggested that DHP regulates the prostaglandin pathway in the neuroendocrine system of teleost fish.

An Attempt to Identify the Medaka Receptor for Somatolactin Alpha Using a Reverse Genetics Approach

Somatolactin alpha (SLα) is a fish-specific hormone involved in body color regulation. The growth hormone (GH) is another hormone that is expressed in all vertebrates and promotes growth. These peptide hormones act by binding to receptors (SLα receptor (SLR) and GH receptor (GHR)); however, the relationships between these ligands and their receptors vary among species. Here, we first performed phylogenetic tree reconstruction by collecting the amino-acid sequences classified as SLR, GHR, or GHR-like from bony fish. Second, we impaired SLR or GHR functions in medaka (Oryzias sakaizumii) using CRISPR/Cas9. Lastly, we analyzed SLR and GHR mutants for phenotypes to deduce their functions. Phylogenetic tree reconstruction was performed using a total of 222 amino-acid sequences from 136 species, which revealed that many GHRa and GHRb are vaguely termed as GHR or GHR-like, while showing no orthologous/paralogous relationships. SLR and GHR mutants were successfully established for phenotyping. SLR mutants exhibited premature lethality after hatching, indicating an essential role for SLR in normal growth. GHR mutations did not affect viability, body length, or body color. These results provide no evidence that either SLR or GHR functions as a receptor for SLα; rather, phylogenetically and functionally, they seem to be receptors for GH, although their (subfunctionalized) roles warrant further investigation.

Evolution of Vertebrate Hormones and Their Receptors: Insights from Non-Osteichthyan Genomes

Homeostatic control and reproductive functions of humans are regulated at the molecular levels largely by peptide hormones secreted from endocrine and/or neuroendocrine cells in the central nervous system and peripheral organs. Homologs of those hormones and their receptors function similarly in many vertebrate species distantly related to humans, but the evolutionary history of the endocrine system involving those factors has been obscured by the scarcity of genome DNA sequence information of some taxa that potentially contain their orthologs. Focusing on non-osteichthyan vertebrates, namely jawless and cartilaginous fishes, this article illustrates how investigating genome sequence information assists our understanding of the diversification of vertebrate gene repertoires in four broad themes: (a) the presence or absence of genes, (b) multiplication and maintenance of paralogs, (c) differential fates of duplicated paralogs, and (d) the evolutionary timing of gene origins.

Molecular targets of prolactin in mummichogs (Fundulus heteroclitus): Ion transporters/channels, aquaporins, and claudins

Prolactin (Prl) was identified over 60 years ago in mummichogs (Fundulus heteroclitus) as a "freshwater (FW)-adapting hormone", yet the cellular and molecular targets of Prl in this model teleost have remained unknown. Here, we conducted a phylogenetic analysis of two mummichog Prl receptors (Prlrs), designated Prlra and Prlrb, prior to describing the tissue- and salinity-dependent expression of their associated mRNAs. We then administered ovine Prl (oPrl) to mummichogs held in brackish water and characterized the expression of genes associated with FW- and seawater (SW)-type ionocytes. Within FW-type ionocytes, oPrl stimulated the expression of Na⁺/Cl^- cotransporter 2 (ncc2) and aquaporin 3 (aqp3). Alternatively, branchial Na⁺/H⁺ exchanger 2 and -3 (nhe2 and -3) expression did not respond to oPrl. Gene transcripts associated with SW-type ionocytes, including Na⁺/K⁺/2Cl^- cotransporter 1 (nkcc1), cystic fibrosis transmembrane regulator 1 (cftr1), and claudin 10f (cldn10f) were reduced by oPrl. Isolated gill filaments incubated with oPrl in vitro exhibited elevated ncc2 and prlra expression. Given the role of Aqps in supporting gastrointestinal fluid absorption, we assessed whether several intestinal aqp transcripts were responsive to oPrl and found that aqp1a and -8 levels were reduced by oPrl. Our collective data indicate that Prl promotes FW-acclimation in mummichogs by orchestrating the expression of solute transporters/channels, water channels, and tight-junction proteins across multiple osmoregulatory organs.

Targeted Delivery of Erythropoietin Hybridized with Magnetic Nanocarriers for the Treatment of Central Nervous System Injury: A Literature Review

Although the incidence of central nervous system injuries has continued to rise, no promising treatments have been elucidated. Erythropoietin plays an important role in neuroprotection and neuroregeneration as well as in erythropoiesis. Moreover, the current worldwide use of erythropoietin in the treatment of hematologic diseases allows for its ready application in patients with central nervous system injuries. However, erythropoietin has a very short therapeutic time window (within 6–8 hours) after injury, and it has both hematopoietic and nonhematopoietic receptors, which exhibit heterogenic and phylogenetic differences. These differences lead to limited amounts of erythropoietin binding to in situ erythropoietin receptors. The lack of high-quality evidence for clinical use and the promising results of in vitro/in vivo models necessitate fast targeted delivery agents such as nanocarriers. Among current nanocarriers, noncovalent polymer-entrapping or polymer-adsorbing erythropoietin obtained by nanospray drying may be the most promising. With the incorporation of magnetic nanocarriers into an erythropoietin polymer, spatiotemporal external magnetic navigation is another area of great interest for targeted delivery within the therapeutic time window. Intravenous administration is the most readily used route. Manufactured erythropoietin nanocarriers should be clearly characterized using bioengineering analyses of the in vivo size distribution and the quality of entrapment or adsorption. Further preclinical trials are required to increase the therapeutic bioavailability (in vivo biological identity alteration, passage through the lung capillaries or the blood brain barrier, and timely degradation followed by removal of the nanocarriers from the body) and decrease the adverse effects (hematological complications, neurotoxicity, and cytotoxicity), especially of the nanocarrier.

Indel variants within the PRL and GHR genes associated with sheep litter size

Growth hormone and prolactin belong to the class of peptide hormones that have a wide range of regulatory functions. In this study, polymorphisms of growth hormone receptor (GHR) and prolactin (PRL) genes were analysed as candidate genes, which are responsible for the litter size in Australian White (AUW) sheep. According to the statistical analyses results, the polymorphism information content (PIC) values of the PRL-P1-ins-23 bp, GHR-P2-del-23 bp and GHR-P8-del-23 bp were 0.371, 0.366 and 0.375, respectively, which indicates the high genetic polymorphism in AUW sheep. Moreover, all indel loci are not conformed to the HWE (p < .05). Further, our findings revealed that the PRL-P1-ins-23 bp polymorphism in the ovine PRL gene was significantly related to the first parity litter size (p = .001) and the DD genotype displaying the highest genotypic mean. Meanwhile, the GHR-P2-del-23 bp and GHR-P8-23 bp indels in the ovine GHR gene were significantly correlated with first parity litter size (p < .05), and the individuals with the genotype II showed significantly higher litter size than others. Collectively, these results demonstrated that our findings could be useful for future sheep breeding strategies based on the molecular-assisted selection (MAS).

Bioluminescence in lanternsharks: Insight from hormone receptor localization

As part of the study of their bioluminescence, the deep-sea lanternshark Etmopterus spinax and Etmopterus molleri (Chondrichthyes, Etmopteridae) received growing interest over the past ten years. These mesopelagic sharks produce light thanks to a finely tuned hormonal control involving melatonin, adrenocorticotropic hormone and α-melanocyte-stimulating hormone. Receptors of these hormones, respectively the melatonin receptors and the melanocortin receptors, are all members of the G-protein coupled receptor family i.e. coupled with specific G proteins involved in the preliminary steps of their transduction pathways. The present study highlights the specific localization of the hormonal receptors, as well as of their associated G-proteins within the light organs, the so-called photophores, in E. spinax and E. molleri through immunohistofluorescence technic. Our results allow gaining insight into the molecular actors and mechanisms involved in the control of the light emission in Etmopterid sharks.

Association between variations of physiological prolactin serum levels and the risk of type 2 diabetes: A systematic review and meta-analysis

AIM

To determine the pooled association between variations of prolactin serum levels within the physiological range and the risk of type 2 diabetes mellitus (T2D).

METHODS

Pubmed, Scopus, Web of Science, and grey literature were searched for studies investigating the association between variations of prolactin serum levels in the normal range and the risk of T2D in adults. The risk of prevalent and incident T2D was summarized as the odds ratio or relative risk according to the quartile of prolactin serum concentration, using random-effects meta-analysis.

RESULTS

Of 2,014 articles identified, 6 met the inclusion criteria. Data were pooled from cross-sectional studies including 6,670 subjects and longitudinal studies involving 13,203 subjects. Men with prolactin levels in the fourth quartile versus those in the first quartile had decreased risk of prevalent T2D (OR 0.52; 95%CI 0.35-077). The same association was seen in women (OR 0.46; 95%CI 0.30-0.73). Conversely, prolactin levels in the fourth versus first quartile were not associated with the risk of incident T2D in men (RR 1.21; 95%CI 0.79-1.87) or women (RR 0.77; 95%CI 0.48-1.22).

CONCLUSION

Higher prolactin serum levels within the normal range were associated with reduced risk of prevalent but not incident T2D. Further studies are necessary to address whether this association is causal, but these findings raise the discussion regarding the optimal level of prolactin suppression in subjects undergoing therapy with dopaminergic agonists.

Secretion and Function of Pituitary Prolactin in Evolutionary Perspective

The hypothalamo-pituitary system developed in early vertebrates. Prolactin is an ancient vertebrate hormone released from the pituitary that exerts particularly diverse functions. The purpose of the review is to take a comparative approach in the description of prolactin, its secretion from pituitary lactotrophs, and hormonal functions. Since the reproductive and osmoregulatory roles of prolactin are best established in a variety of species, these functions are the primary subjects of discussion. Different types of prolactin and prolactin receptors developed during vertebrate evolution, which will be described in this review. The signal transduction of prolactin receptors is well conserved among vertebrates enabling us to describe the whole subphylum. Then, the review focuses on the regulation of prolactin release in mammals as we have the most knowledge on this class of vertebrates. Prolactin secretion in response to different reproductive stimuli, such as estrogen-induced release, mating, pregnancy and suckling is detailed. Reproduction in birds is different from that in mammals in several aspects. Prolactin is released during incubation in avian species whose regulation and functional significance are discussed. Little information is available on prolactin in reptiles and amphibians; therefore, they are mentioned only in specific cases to explain certain evolutionary aspects. In turn, the osmoregulatory function of prolactin is well established in fish. The different types of pituitary prolactin in fish play particularly important roles in the adaptation of eutherian species to fresh water environments. To achieve this function, prolactin is released from lactotrophs in hyposmolarity, as they are directly osmosensitive in fish. In turn, the released prolactin acts on branchial epithelia, especially ionocytes of the gill to retain salt and excrete water. This review will highlight the points where comparative data give new ideas or suggest new approaches for investigation in other taxa.

Inter-individual variability in freshwater tolerance is related to transcript level differences in gill and posterior kidney of European sea bass

Acclimation to low salinities is a vital physiological challenge for euryhaline fish as the European sea bass Dicentrarchus labrax. This species undertakes seasonal migrations towards lagoons and estuaries where a wide range of salinity variations occur along the year. We have previously reported intraspecific differences in freshwater tolerance, with an average 30% mortality rate. In this study, we bring new evidence of mechanisms underlying freshwater tolerance in sea bass at gill and kidney levels. In fresh water (FW), intraspecific differences in mRNA expression levels of several ion transporters and prolactin receptors were measured. We showed that the branchial Cl^-/HCO₃^- anion transporter (slc26a6c) was over-expressed in freshwater intolerant fish, probably as a compensatory response to low blood chloride levels and potential metabolic alkalosis. Moreover, prolactin receptor a (prlra) and Na⁺/Cl^- cotransporter (ncc1) but not ncc-2a expression seemed to be slightly increased and highly variable between individuals in freshwater intolerant fish. In the posterior kidney, freshwater intolerant fish exhibited differential expression levels of slc26 anion transporters and Na⁺/K⁺/2Cl^- cotransporter 1b (nkcc1b). Lower expression levels of prolactin receptors (prlra, prlrb) were measured in posterior kidney which probably contributes to the failure in ion reuptake at the kidney level. Freshwater intolerance seems to be a consequence of renal failure of ion reabsorption, which is not sufficiently compensated at the branchial level.

Divergent genes encoding the putative receptors for growth hormone and prolactin in sea lamprey display distinct patterns of expression

Growth hormone receptor (GHR) and prolactin receptor (PRLR) in jawed vertebrates were thought to arise after the divergence of gnathostomes from a basal vertebrate. In this study we have identified two genes encoding putative GHR and PRLR in sea lamprey (Petromyzon marinus) and Arctic lamprey (Lethenteron camtschaticum), extant members of one of the oldest vertebrate groups, agnathans. Phylogenetic analysis revealed that lamprey GHR and PRLR cluster at the base of gnathostome GHR and PRLR clades, respectively. This indicates that distinct GHR and PRLR arose prior to the emergence of the lamprey branch of agnathans. In the sea lamprey, GHR and PRLR displayed a differential but overlapping pattern of expression; GHR had high expression in liver and heart tissues, whereas PRLR was expressed highly in the brain and moderately in osmoregulatory tissues. Branchial PRLR mRNA levels were significantly elevated by stage 5 of metamorphosis and remained elevated through stage 7, whereas levels of GHR mRNA were only elevated in the final stage (7). Branchial expression of GHR increased following seawater (SW) exposure of juveniles, but expression of PRLR was not significantly altered. The results indicate that GHR and PRLR may both participate in metamorphosis and that GHR may mediate SW acclimation.

Somatotropic Axis Regulation Unravels the Differential Effects of Nutritional and Environmental Factors in Growth Performance of Marine Farmed Fishes

The Gh/Prl/Sl family has evolved differentially through evolution, resulting in varying relationships between the somatotropic axis and growth rates within and across fish species. This is due to a wide range of endogenous and exogenous factors that make this association variable throughout season and life cycle, and the present minireview aims to better define the nutritional and environmental regulation of the endocrine growth cascade over precisely defined groups of fishes, focusing on Mediterranean farmed fishes. As a result, circulating Gh and Igf-i are revitalized as reliable growth markers, with a close association with growth rates of gilthead sea bream juveniles with deficiency signs in both macro- or micro-nutrients. This, together with other regulated responses, promotes the use of Gh and Igf-i as key performance indicators of growth, aerobic scope, and nutritional condition in gilthead sea bream. Moreover, the sirtuin-energy sensors might modulate the growth-promoting action of somatotropic axis. In this scenario, transcripts of igf-i and gh receptors mirror changes in plasma Gh and Igf-i levels, with the ghr-i/ghr-ii expression ratio mostly unaltered over season. However, this ratio is nutritionally regulated, and enriched plant-based diets or diets with specific nutrient deficiencies downregulate hepatic ghr-i, decreasing the ghr-i/ghr-ii ratio. The same trend, due to a ghr-ii increase, is found in skeletal muscle, whereas impaired growth during overwintering is related to increase in the ghr-i/ghr-ii and igf-ii/igf-i ratios in liver and skeletal muscle, respectively. Overall, expression of insulin receptors and igf receptors is less regulated, though the expression quotient is especially high in the liver and muscle of sea bream. Nutritional and environmental regulation of the full Igf binding protein 1-6 repertoire remains to be understood. However, tissue-specific expression profiling highlights an enhanced and nutritionally regulated expression of the igfbp-1/-2/-4 clade in liver, whereas the igfbp-3/-5/-6 clade is overexpressed and regulated in skeletal muscle. The somatotropic axis is, therefore, highly informative of a wide-range of growth-disturbing and stressful stimuli, and multivariate analysis supports its use as a reliable toolset for the assessment of growth potentiality and nutrient deficiencies and requirements, especially in combination with selected panels of other nutritionally regulated metabolic biomarkers.