Sequences of pituitary and placental lactogenic and growth hormones: evolution from a primordial peptide by gene reduplication

Prolactin and Growth Hormone Signaling and Interlink Focused on the Mammosomatotroph Paradigm: A Comprehensive Review of the Literature

Prolactin (PRL) and growth hormone (GH) are peptide hormones that bind to the class 1 cytokine receptor superfamily, a highly conserved cell surface class of receptors. Both hormones control their own secretion via a negative autocrine loop in their own mammosomatotroph, lactotroph or somatotroph. In this regard, GH and PRL are regulated by similar signaling pathways involving cell growth and hormone secretion. Thus, GH and PRL dysregulation and pituitary neuroendocrine tumor (PitNET) development may have common pathogenic pathways. Based on cell linage, lactotroph and somatotroph PitNETs come from pituitary-specific POU-class homeodomain transcription factor (Pit-1). Mammosomatotroph and plurihormonal PitNETs are a unique subtype of PitNETs that arise from a single-cell population of Pit-1 lineage. In contrast, mixed somatotroph-lactotroph PitNETs are composed of two distinct cell populations: somatotrophs and lactotrophs. Morphologic features that distinguish indolent PitNETs from locally aggressive ones are still unidentified, and no single prognostic parameter can predict tumor aggressiveness or treatment response. In this review, we aim to explore the latest research on lactotroph and somatotroph PitNETs, the molecular mechanisms involved in PRL and GH axis regulation and the signaling pathways involved in their aggressiveness, particularly focused on mammosomatotroph and mixed subtypes. Finally, we summarize epidemiological, clinical, and radiological features of these exceptional tumors. We aim to shed light, from basic to clinical settings, on new perspectives and scientific gaps in this field.

Prolactin response to growth hormone stimulation tests

BACKGROUND

Despite many similarities between the structure, receptors, proliferative and growth promoting actions, the relationship between Prolactin (PRL) and Growth Hormone (GH) in clinical conditions has received little attention.

OBJECTIVE

To determine the PRL response to GH stimulation tests.

SUBJECTS

Prepubertal and early pubertal boys (n = 581) and girls (n = 502) with idiopathic, non-syndromatic short stature.

DESIGN

Data was retrieved from the computerized records of the Endocrine Laboratory, Schneider Children's Medical Center. Peak GH and PRL levels during GH stimulation tests with glucagon (Gluc), Clonidine (Clon) and Clonidine with arginine (Clon+Arg), were compared. Both PRL and GH were determined by radioimmunoassay.

RESULTS

Whereas Gluc stimulated both GH and PRL to similar levels, Clon alone or combined with Arg suppressed the PRL secretion (p < 0.0001). It is also evident that in both boys and girls Clon alone and Clon±Arg are superior to Gluc in GH stimulation. The higher GH levels during Clon+Arg than with Clon alone are attributed to the pubertal stage.

CONCLUSION

This study provides further information on the Prolactin-Growth hormone relationship in children.

Association analysis of prolactin and prolactin receptor genes with selected productive and reproductive traits in Egyptian buffalo

A total of 266 records of buffalo raised in two experimental herds in Egypt were assessed to detect prolactin (PRL) and prolactin receptor (PRLR) genes' polymorphism using PCR-Single Strand Conformational Polymorphism (SSCP) and PCR-Restricted Fragment Length Polymorphism (RFLP) techniques as well as to investigate their association with calf birth weight (BW), weaning weight (WW), lactation period (LP), total milk yield (TMY), stillbirth, calving ease (CE), gestation length (GL), postpartum interval to pregnancy (PPIP), calving interval (CI), and age at first calving (AFC). Predicted breeding values were estimated and used in the association with detected genotypes. A monomorphic pattern of the studied PRL 156 bp segment was recorded and absence of its polymorphism in buffalo was corroborated. We also determined polymorphism of PRLR reflected in three loci: PRLR2, PRLR4, and PRLR9. Significant differences among PRLP9 genotypes (AA, AB, and BB) were displayed for all studied traits as well as among PRLR2 genotypes, except for CE, while PRLR4 genotypes significantly differed only in BW, WW, TMY, stillbirth, GL, and AFC. In practice, strong associations among genotypes of the PRLR gene and the traits of interest candidate this gene to be selective in Egyptian buffalo breeding for improving both productive and reproductive traits.

Prolactin from Pluripotency to Central Nervous System Development

Prolactin (PRL) is a versatile hormone that exerts more than 300 functions in vertebrates, mainly associated with physiological effects in adult animals. Although the process that regulates early development is poorly understood, evidence suggests a role of PRL in the early embryonic development regarding pluripotency and nervous system development. Thus, PRL could be a crucial regulator in oocyte preimplantation and maturation as well as during diapause, a reversible state of blastocyst development arrest that shares metabolic, transcriptomic, and proteomic similarities with pluripotent stem cells in the naïve state. Thus, we analyzed the role of the hormone during those processes, which involve the regulation of its receptor and several signaling cascades (Jak/Mapk, Jak/Stat, and PI3k/Akt), resulting in either a plethora of physiological actions or their dysregulation, a factor in developmental disorders. Finally, we propose models to improve the knowledge on PRL function during early development.

Prolactin receptor regulates the seasonal reproduction of striped hamsters

In this study, differential mRNA expression patterns of prolactin receptor (PRLR) in the hypothalamus and gonads, and the correlation with follicle stimulating hormone (FSH) and luteinizing hormone (LH) in striped hamster serum from spring, summer, autumn and winter were analyzed. Mature female and male striped hamsters in oestrus were used. Expression levels of PRLR in the hypothalamus, ovaries and testis from the summer and winter individuals were significantly higher compared with levels from the spring and autumn, whereas FSH and LH serum concentrations from summer and winter individuals were significantly lower compared with that from the spring and autumn. PRLR expression levels in hypothalamus, ovaries and testis were negatively correlated with FSH and LH serum concentrations, illustrating that PRLR might negatively regulate seasonal reproductive activity. PRLR expression levels in ovaries and testes were significantly higher compared with levels in the hypothalamus, suggesting that the regulative effects of PRLR in gonads might be significantly higher compared with that in the hypothalamus. Furthermore, PRLR expression levels from the spring, summer, autumn and winter seasons in the hypothalamus and gonads were significantly higher in females compared with levels in males, indicating that the regulative effect of PRLR might be sex dependent. Taken together, this study helps to understand in depth the seasonal regulative reproduction mechanism of striped hamsters to reasonably control population abundance.

Short stature explained by dimerization of human growth hormone induced by a p.C53S point mutation

A homozygous mutation in growth hormone 1 (GH1) was recently identified in an individual with growth failure. This mutation, c.705G>C, causes replacement of cysteine at position 53 of the 191-amino-acid sequence of 22 kDa human GH (hGH) with serine (p.C53S). This hGH molecule (hereafter referred to as GH-C53S) lacks the disulfide bond between p.Cys-53 and p.Cys-165, which is highly conserved among species. It has been reported previously that monomeric GH-C53S has reduced bioactivity compared with WT GH (GH-WT) because of its decreased ability to bind and activate the GH receptor in vitro In this study, we discovered that substitution of p.Cys-53 in hGH significantly increased formation of hGH dimers in pituitary cells. We expressed His-tagged hGH variants in the cytoplasm of genetically modified Rosetta-gami B DE3 Escherichia coli cells, facilitating high-yield production. We observed that the bioactivity of monomeric GH-C53S is 25.2% of that of GH-WT and that dimeric GH-C53S-His has no significant bioactivity in cell proliferation assays. We also found that the expression of GH-C53S in pituitary cells deviates from that of GH-WT. GH-C53S was exclusively stained in the Golgi apparatus, and no secretory granules formed for this variant, impairing its stimulated release. In summary, the unpaired Cys-165 in GH-C53S forms a disulfide bond linking two hGH molecules in pituitary cells. We conclude that the GH-C53S dimer is inactive and responsible for the growth failure in the affected individual.

The role of prolactin in co-ordinating fertility and metabolic adaptations during reproduction

Mammalian pregnancy and lactation is accompanied by a period of infertility that takes place in the midst of a sustained increase in food intake. Indeed, successful reproduction in females is dependent on co-ordination of the distinct systems that regulate reproduction and metabolism. Rather than arising from different mechanisms during pregnancy and lactation, we propose that elevations in lactogenic hormones (predominant among these being prolactin and the placental lactogens), are ideally placed to influence both of these systems at the appropriate time. We review the literature examining the impacts of lactogens on fertility and energy homeostasis in the virgin state, during pregnancy and lactation and potential long-term impacts of reproductive experience. Taken together, the literature indicates that duration and pattern of lactogen exposure is a vital factor in the ability of these hormones to alter reproduction and food intake. Transient increases in prolactin, as typically seen in healthy virgin females and males, are unable to exert lasting impacts. Importantly, both suppression of fertility and increased food intake are only observed following exposure to chronically-elevated levels of lactogens. Physiologically, the only time this pattern of lactogenic secretion is maintained in the healthy female is during pregnancy and lactation, when co-ordination between these regulatory systems emerges. This article is part of the special issue on 'Neuropeptides'.

Acute effects of somatomammotropin hormones on neuronal components of the hypothalamic-pituitary-gonadal axis

Growth hormone (GH) and prolactin (PRL) are known as pleiotropic hormones. Accordingly, the distribution of their receptors comprises several organs and tissues, including the central nervous system. The appropriate secretion of both hormones is essential for sexual maturation and maintenance of reproductive functions, while defects in their secretion affect puberty onset and can cause infertility. Conversely, GH therapy at a prepubertal age may accelerate puberty. On the other hand, hyperprolactinemia is a frequent cause of infertility. While the action of PRL in some central components of the Hypothalamic-Pituitary-Gonadal (HPG) axis, such as the kisspeptin neurons, has been well documented, the possible effects of GH in the hypothalamus are still elusive. Thus, the present study was designed to investigate whether somatomammotropin hormones are able to modulate the activity of critical neuronal components of the HPG axis, including kisspeptin neurons and cells of the ventral premammillary nucleus (PMv). Our results revealed that GH effects in kisspeptin neurons of the anteroventral periventricular and rostral periventricular nuclei or in PMv neurons relies predominantly on the recruitment of the signal transducer and activator of transcription 5 (STAT5) rather than through acute changes in resting membrane potential. Importantly, kisspeptin neurons located at the arcuate nucleus were not directly responsive to GH. Additionally, our findings further identified PMv neurons as potential targets of PRL, since PRL induces the phosphorylation of STAT5 and depolarizes PMv neurons. Combined, our data provide evidence that GH and PRL may affect the HPG axis via specific hypothalamic neurons.

Hormonal pleiotropy and the evolution of allocation trade-offs

Recent empirical evidence suggests that trade-off relationships can evolve, challenging the classical image of their high entrenchment. For energy reliant traits, this relationship should depend on the endocrine system that regulates resource allocation. Here, we model changes in this system by mutating the expression and conformation of its constitutive hormones and receptors. We show that the shape of trade-offs can indeed evolve in this model through the combined action of genetic drift and selection, such that their evolutionarily expected curvature and length depend on context. In particular, the shape of a trade-off should depend on the cost associated with resource storage, itself depending on the traded resource and on the ecological context. Despite this convergence at the phenotypic level, we show that a variety of physiological mechanisms may evolve in similar simulations, suggesting redundancy at the genetic level. This model should provide a useful framework to interpret and unify the overly complex observations of evolutionary endocrinology and evolutionary ecology.

Asymmetry between Activation and Deactivation during a Transcriptional Pulse

Transcription in eukaryotic cells occurs in gene-specific bursts or pulses of activity. Recent studies identified a spectrum of transcriptionally active “on-states,” interspersed with periods of inactivity, but these “off-states” and the process of transcriptional deactivation are poorly understood. To examine what occurs during deactivation, we investigate the dynamics of switching between variable rates. We measured live single-cell expression of luciferase reporters from human growth hormone or human prolactin promoters in a pituitary cell line. Subsequently, we applied a statistical variable-rate model of transcription, validated by single-molecule FISH, to estimate switching between transcriptional rates. Under the assumption that transcription can switch to any rate at any time, we found that transcriptional activation occurs predominantly as a single switch, whereas deactivation occurs with graded, stepwise decreases in transcription rate. Experimentally altering cAMP signalling with forskolin or chromatin remodelling with histone deacetylase inhibitor modifies the duration of defined transcriptional states. Our findings reveal transcriptional activation and deactivation as mechanistically independent, asymmetrical processes.

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Gene transcription switches between variable rates

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Single-cell microscopy and mathematical modeling quantifies switch dynamics

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We observe an asymmetry in the activation/deactivation of transcriptional bursts

A Common Phenotype Polymorphism in Mammalian Brains Defined by Concomitant Production of Prolactin and Growth Hormone

Pituitary Prolactin (PRL) and Growth Hormone (GH) are separately controlled and sub-serve different purposes. Surprisingly, we demonstrate that extra-pituitary expression in the adult mammalian central nervous system (CNS) is coordinated at mRNA and protein levels. However this was not a uniform effect within populations, such that wide inter-individual variation was superimposed on coordinate PRL/GH expression. Up to 44% of individuals in healthy cohorts of mice and rats showed protein levels above the norm and coordinated expression of PRL and GH transcripts above baseline occurred in the amygdala, frontal lobe and hippocampus of 10% of human subjects. High levels of PRL and GH present in post mortem tissue were often presaged by altered responses in fear conditioning and stress induced hyperthermia behavioral tests. Our data define a common phenotype polymorphism in healthy mammalian brains, and, given the pleiotropic effects known for circulating PRL and GH, further consequences of coordinated CNS over-expression may await discovery.

Principles of the prolactin/vasoinhibin axis

The hormonal family of vasoinhibins, which derive from the anterior pituitary hormone prolactin, are known for their inhibiting effects on blood vessel growth, vasopermeability, and vasodilation. As pleiotropic hormones, vasoinhibins act in multiple target organs and tissues. The generation, secretion, and regulation of vasoinhibins are embedded into the organizational principle of an axis, which integrates the hypothalamus, the pituitary, and the target tissue microenvironment. This axis is designated as the prolactin/vasoinhibin axis. Disturbances of the prolactin/vasoinhibin axis are associated with the pathogenesis of retinal and cardiac diseases and with diseases occurring during pregnancy. New phylogenetical, physiological, and clinical implications are discussed.

Expression of human growth hormone in the milk of transgenic rabbits with transgene mapped to the telomere region of chromosome 7q

The advent of transgenic technology has provided methods for the production of pharmaceuticals by the isolation of these proteins from transgenic animals. The mammary gland has been focused on as a bioreactor, since milk is easily collected from lactating animals and protein production can be expressed at very high levels, including hormones and enzymes. We demonstrate here the expression pattern of recombinant human growth hormone (rhGH) in transgenic rabbits carrying hGH genomic sequences driven by the rat whey acidic protein (WAP) promoter. The transgene was mapped to the q26-27 telomere region of chromosome 7q by fluorescence in situ hybridization (FISH). Nearly 30 % of the F1 generation demonstrated the presence of transgene. The recombinant growth hormone was detected in the milk of the transgenic rabbit females, but not in serum, up to the level of 10 μg/ml. Ectopic expression of the transgene in the brain, heart, kidney, liver, and salivary gland was not observed, indicating that a short sequence of rat WAP promoter (969 bp) contained essential sequences directing expression exclusively to the mammary gland. The biological activity of recombinant growth hormone was measured by immunoreactivity and the capability to stimulate growth of the hormone-dependent Nb211 cell line.

Elephant transcriptome provides insights into the evolution of eutherian placentation

The chorioallantoic placenta connects mother and fetus in eutherian pregnancies. In order to understand the evolution of the placenta and provide further understanding of placenta biology, we sequenced the transcriptome of a term placenta of an African elephant (Loxodonta africana) and compared these data with RNA sequence and microarray data from other eutherian placentas including human, mouse, and cow. We characterized the composition of 55,910 expressed sequence tag (i.e., cDNA) contigs using our custom annotation pipeline. A Markov algorithm was used to cluster orthologs of human, mouse, cow, and elephant placenta transcripts. We found 2,963 genes are commonly expressed in the placentas of these eutherian mammals. Gene ontology categories previously suggested to be important for placenta function (e.g., estrogen receptor signaling pathway, cell motion and migration, and adherens junctions) were significantly enriched in these eutherian placenta–expressed genes. Genes duplicated in different lineages and also specifically expressed in the placenta contribute to the great diversity observed in mammalian placenta anatomy. We identified 1,365 human lineage–specific, 1,235 mouse lineage–specific, 436 cow lineage–specific, and 904 elephant-specific placenta-expressed (PE) genes. The most enriched clusters of human-specific PE genes are signal/glycoprotein and immunoglobulin, and humans possess a deeply invasive human hemochorial placenta that comes into direct contact with maternal immune cells. Inference of phylogenetically conserved and derived transcripts demonstrates the power of comparative transcriptomics to trace placenta evolution and variation across mammals and identified candidate genes that may be important in the normal function of the human placenta, and their dysfunction may be related to human pregnancy complications.

Evolution of GnRH: diving deeper

Gonadotropin-releasing hormone (GnRH) plays a central role in vertebrate reproduction. The evolutionary origin of this neuropeptide and its receptor is not obvious, but the advent of genomics makes it possible to examine the roots of GnRH and delve deeper into its ancestral relationships. New peptide sequences identified in invertebrates from annelids to tunicates reveal GnRH-like peptides of 10-12 amino acids. Structural conservation suggests homology between the 15 known invertebrate peptides and the 15 known vertebrate GnRHs. The functions of the invertebrate GnRH-like peptides are not necessarily related to reproduction. We suggest that structurally related families of invertebrate peptides including corazonin and adipokinetic hormone (AKH) form a superfamily of neuropeptides with the GnRH family. GnRH receptors have also been identified in invertebrates from annelids to tunicates suggesting that the origin of GnRH and its receptor extends deep in evolution to the origin of bilaterian animals. To resolve the relationship of invertebrate and vertebrate receptors, we conducted large-scale phylogenetic analysis using maximum likelihood. The data support a superfamily that includes GnRH, AKH and corazonin receptors derived from both published sequences and unpublished gene model predictions. Closely related to the GnRHR superfamily is the vasopressin/oxytocin superfamily of receptors. Phylogenetic analysis suggests a shared ancestry with deep roots. A functional role for GnRH in vertebrates or invertebrates leads to questions about the evolutionary origin of the pituitary. Our analysis suggests a functioning pituitary was the result of genomic duplications in early vertebrates.

Short stature and metabolic abnormalities in two sisters with a 7.6-kb GH1 gene deletion

Growth hormone 1 (GH1) gene deletions occur in approximately 10-15% of patients with severe isolated, GH deficiency (GHD). The standard treatment for GHD is GH replacement. Individuals with GH gene defects, however, may form GH antibodies that interfere with the efficacy of exogenous recombinant GH (rhGH) therapy.

OBJECTIVE

We describe the growth measures and metabolic studies of two Hispanic sisters with the same 7.6-kb GH1 gene deletion who presented with short stature and increased body fat, and who developed neutralizing GH antibodies secondary to rhGH exposure.

DESIGN

The younger sister has now been treated with recombinant human insulin-like growth factor-I (rhIGF-I) for 4 years, and is continuing treatment. The older sister was not given rhIGF-I based on her normal height velocity and age. After the first 4 years of rhIGF-I treatment of the younger sister, we summarized the longitudinal anthropometric measures and serial laboratory studies, including GH surrogates, fasting lipid studies, oral glucose tolerance tests, and HbA1c, of both sisters. Body composition was quantified using DEXA analysis.

RESULTS

The older sister achieved an adult stature at the low end of her mid-parental target height range, having been treated only with rhGH for ~2.5 years (between 11 months and 3.5 years of age). Treatment of the younger sister with rhIGF-I for 4 years has led to persistent improvement in height velocity, but was associated with adverse short-term effects on all lipids. Her BMI increased modestly (+4.1 kg/m(2)) during rhIGF-I treatment, though her change in percent body fat was negligible by DEXA (Δ -0.7%).

CONCLUSIONS

In individuals with a GH gene deletion, rhIGF-I promotes increased height velocity, but may be associated with adverse effects on lipids and BMI. It is clear that the long-term effects of rhIGF-I on lipid metabolism and body composition require further monitoring and assessment with continued treatment.

Cloning and expression of cDNA for salmon growth hormone in Escherichia coli

cDNA clones encoding chum salmon (Oncorhynchus keta) growth hormone (sGH) have been isolated from a cDNA library prepared from chum salmon pituitary gland poly(A)(+) RNA. Synthetic oligodeoxynucleotide mixtures based on amino acid residues 23-28 of sGH were used as hybridization probes to select recombinant plasmids carrying the sGH coding sequence. The complete nucleotide sequence of sGH cDNA has been determined. The cDNA sequence codes for a polypeptide of 210 amino acids, including a putative signal sequence of 22 amino acids. The 5' and 3' untranslated regions of the message were 64 and 426 bases long, respectively. Mature sGH was efficiently expressed in Escherichia coli carrying a plasmid in which the sGH cDNA was under control of the E. coli trp promoter; sGH comprised about 15% of the total cellular protein in such bacteria. The partially purified sGH from E. coli stimulated the growth of rainbow trout and the activity was indistinguishable from that of natural sGH.

Restriction fragment length polymorphisms in dairy and beef cattle at the growth hormone and prolactin loci

Two bovine populations, a Holstein-Friesian dairy stock and a synthetic (Baladi X Hereford X Simmental X Charolais) beef stock, were screened for restriction fragment length polymorphisms (RFLPs) at the growth hormone and prolactin genes. Most RFLPs at the growth hormone gene are apparently the consequence of an insertion/deletion event which was localized to a region downstream of the structural gene. The restriction map for the genomic region including the growth hormone gene was extended. Two HindIII RFLPs at the growth hormone locus, as well as several RFLPs at the prolactin gene, seemed to be the consequence of a series of point mutations. The results are discussed in terms of the possibility that minor genomic variability underlies quantitative genetic variation.

Mapping of bovine prolactin and rhodopsin genes in hybrid somatic cells

The genes encoding bovine prolactin and rhodopsin were assigned to syntenic groups on the basis of hybridization of DNA from a panel of bovine-hamster hybrid somatic cell lines with cloned prolactin and rhodopsin gene probes. Prolactin was found to be syntenic with previously mapped glyoxalase, BoLA and 21-hydroxylase genes, establishing a syntenic conservation with human chromosome 6. The presence of bovine rhodopsin sequences among the various hybrid cell lines was not concordant with any gene previously assigned to one of the 23 defined autosomal syntenic groups. Thus, rhodopsin marks a new bovine syntenic group, U24, leaving only five cattle autosomes unmarked by at least one biochemical or molecular marker.

Restriction fragment length polymorphisms associated with growth hormone and prolactin genes in Holstein bulls: evidence for a novel growth hormone allele

Sperm DNA isolated from sons of three extensively used US Holstein bulls was screened for differences associated with the primary gene structure of the bovine growth hormone (bGH) and prolactin (bPrl) genes. Southern blot analysis of DNA digested with 10 restriction enzymes revealed that offspring from two of the three bull families exhibited polymorphisms around the bGH and bPrl genes. Restriction fragment length polymorphisms (RFLPs) around the bGH gene were detected with five enzymes, whereas three enzymes revealed RFLPs around the bPrl gene. At least three structural differences were predicted around the bGH gene. The most common variant hybridization pattern appeared to involve an insertion/deletion located downstream of the conserved 3' EcoRI site. The presence of RFLPs in the genes coding for these pituitary hormones within a familial line may provide the basis for genetic markers associated with lactation and mammary development.

Prolactin-dependent modulation of organogenesis in the vertebrate: Recent discoveries in zebrafish

The scientific literature is replete with evidence of the multifarious functions of the prolactin (PRL)/growth hormone (GH) superfamily in adult vertebrates. However, little information is available on the roles of PRL and related hormones prior to the adult stage of development. A limited number of studies suggest that GH functions to stimulate glucose transport and protein synthesis in mouse blastocytes and may be involved during mammalian embryogenesis. In contrast, the evidence for a role of PRL during vertebrate embryogenesis is limited and controversial. Genes encoding GH/PRL hormones and their respective receptors are actively transcribed and translated in various animal models at different time points, particularly during tissue remodeling. We have addressed the potential function of GH/PRL hormones during embryonic development in zebrafish by the temporary inhibition of in vivo PRL translation. This treatment caused multiple morphological defects consistent with a role of PRL in embryonic-stage organogenesis. The affected organs and tissues are known targets of PRL activity in fish and homologous structures in mammalian species. Traditionally, the GH/PRL hormones are viewed as classical endocrine hormones, mediating functions through the circulatory system. More recent evidence points to cytokine-like actions of these hormones through either an autocrine or a paracrine mechanism. In some situations they could mimic actions of developmentally regulated genes as suggested by experiments in multiple organisms. In this review, we present similarities and disparities between zebrafish and mammalian models in relation to PRL and PRLR activity. We conclude that the zebrafish could serve as a suitable alternative to the rodent model to study PRL functions in development, especially in relation to organogenesis.

Molecular evolution of the polypeptide hormones

Any biological function is at least bimolecular and its evolution therefore is at least dual, with variations in two lines of molecules. The hormone specificity results from a particular fit between the three-dimensional structure of the agent and that of the receptor but, because receptors are not known at the structural level, a discussion on the evolution of the polypeptide hormones is mainly limited to the possible progressive changes of the latter. As for other proteins (enzymes, oxygen carriers etc.) two degrees of complexity can be distinguished according to whether the hormone comprises one or several polypeptide chains. Protein assembly can bring new biological properties, each subunit playing a particular role. In this case, the 'internal' evolution (chain-chain interactions) overlaps the 'external' evolution (hormone-receptor contacts). The 'monomeric' hormones present the following problems: evolution of the prohormone and of the converting enzyme (for insulin), duplication and differentiation of two lines of hormones either by amino acid substitutions (neurohypophysial hormones and neurophysins) or by substitutions and size modifications (corticotropin and lipotropin), duplication and fusion leading to internal homology in the single polypeptide chain (somatotropin, prolactin, placental lactogen). The 'dimeric' hormones lead to several problems: successive duplications giving different subunits, selective associations between subunits, unequal rates of evolution of the subunits, the function of each subunit (lutropin, follitropin, thyrotropin, choriogonadotropin). An attempt is made to integrate the evolution of polypeptide hormones in the frame of the evolution of proteins.

Cloning of Russian sturgeon (Acipenser gueldenstaedtii) growth hormone and insulin-like growth factor I and their expression in male and female fish during the first period of growth

In this study, the GH and IGF-I of the Russian sturgeon (rs), Acipenser gueldenstaedtii, were cloned and sequenced, and their mRNA gene expression determined. In addition, to improve our understanding of the GH function, the expression of this hormone was assessed in young males and females. Moreover, IGF-I expression was quantified in young males and compared to that in older ones. The nucleotide sequence of the rsGH cDNA was 980 bp long and had an open reading frame of 642 bp, beginning with the first ATG codon at position 39 and ending with the stop codon at position 683. A putative polyadenylation signal, AATAAA, was recognized 42 bp upstream of the poly (A) tail. The position of the signal- peptide cleavage site was predicted to be at position 111, yielding a signal peptide of 24 amino-acids (aa) and a mature peptide of 190 aa. When the rsGH aa sequence was compared with other species, the highest degree of identity was found to be with mammalians (66-70% identity), followed by anguilliformes and amphibia (61%) and other fish (39-47%). The level of rsGH mRNA was discovered to be similar in pituitaries of females and males of 5 age groups (1, 2, 3, 4, and 5- yr-old). In females and males, the levels did not change dramatically during the first 5 yr of growth. The partial nucleotide sequence of the rsIGF-I was 445 bp long and had an open reading frame of 396 bp, beginning with the ATG codon at position 50. The position of the signal-peptide cleavage site was predicted to be at position 187, yielding a signal peptide of 44 aa. The highest level of IGF-I mRNA expression was recorded in the kidney of adult sturgeons. The IGF-I mRNA expression levels in the intestine, pituitary gland, and liver were not significantly different. Low levels of expression were found in the brain, heart, and muscle. In most tissues, there was no significant difference between mRNA levels of one and 5-yr-old fish. In conclusion, based on the GH-sequence analysis, A. gueldenstaedtii is genetically distant from other teleosts. The expression of the GH mRNA was similar in males and females, and its level remained constant during the first 5 yr of growth. While the IGF-I mRNA expression differed amongst various tissues, the level in each tissue was similar in 1 and 5-yr-old fish.

Down-regulation of goldfish (Carassius auratus) prolactin gene expression by dopamine and thyrotropin releasing hormone

Prolactin (PRL) is the most versatile hormone identified with multiple functions from osmoregulation in euryhaline fish to lactation in mammals. However, little is known about the basic physiological control of PRL in stenohaline freshwater fish. In this study, goldfish is used as a model for the study of PRL gene expression in stenohaline fish. We report herein the identification of the goldfish PRL (gfPRL) genomic sequence which possesses five exons with its 5'-flanking gene promoter region characterized in vitro using GH3 and GH4 cell-lines. Dopamine and thyrotropin releasing hormone were found to down-regulate the transcription of this gfPRL gene promoter in vitro. This was further confirmed by the decrease of PRL mRNA levels in vitro (in goldfish pituitary primary cells) and in vivo (intra-peritoneal injection) following the administrations of dopamine and thyrotropin releasing hormone. The Pit-1 binding sites of gfPRL are highly conserved with a consensus DNA sequence of 5'TATNCAT-3', as confirmed with the electrophoretic mobility shift assay using nuclear extract from the GH3 cell-line, may be responsible for the control of gfPRL gene promoter.

The prolactin family: effectors of pregnancy-dependent adaptations

Prolactin (PRL) is a hormone involved in many biological functions. In some species, there is a family of PRL-related genes; such is the case in the mouse and rat. The actions of members of the PRL family can be distinguished based on the involvement of the PRL receptor signaling pathway (classical versus nonclassical). Recent insights into the biology of the PRL family have been derived from mouse mutagenesis studies. There is compelling evidence suggesting that the PRL family contributes to the regulation of pregnancy-dependent adaptations to physiological stressors.

Neuroendocrine control of growth hormone in fish

The biological actions of growth hormone (GH) are pleiotropic, including growth promotion, energy mobilization, gonadal development, appetite, and social behavior. Accordingly, the regulatory network for GH is complex and includes many endocrine and environmental factors. In fish, the neuroendocrine control of GH is multifactorial with multiple inhibitors and stimulators of pituitary GH secretion. In fish, GH release is under a tonic negative control exerted mainly by somatostatin. Sex steroid hormones and nutritional status influence the level of brain expression and effectiveness of some of these GH neuroendocrine regulatory factors, suggesting that their relative importance differs under different physiological conditions. At the pituitary level, some, if not all, somatotropes can respond to multiple regulators. Therefore, ligand- and function-specificity, as well as the integrative responses to multiple signals must be achieved at the level of signal transduction mechanisms. Results from investigations on a limited number of stimulatory and inhibitory GH-release regulators indicate that activation of different but convergent intracellular pathways and the utilization of specific intracellular Ca(2+) stores are some of the strategies utilized. However, more work remains to be done in order to better understand the integrative mechanisms of signal transduction at the somatotrope level and the relevance of various GH regulators in different physiological circumstances.

Study of goldfish (Carassius auratus) growth hormone structure–function relationship by domain swapping

Using goldfish as a model, the structure-function relationship of goldfish growth hormone was studied using the strategy of homologous domain swapping. Chimeric mutants were constructed by exchanging homologous regions between goldfish growth hormone (gfGH II) and goldfish prolactin (gfPRL) with their cloned complementary DNAs. Six mutants, with their domain-swapped, were generated to have different combinations of three target regions, including the helix a, helix d and the large section in between these helices (possess the helices b, c and other random coiled regions). After expression in E. coli and refolding, these mutants were characterized by using competitive receptor binding assay (RRA) and growth hormone responding promoter activation assay. The different activity profiles of mutants in Spi 2.1 gene promoter assays from that in RRA shows that, for gfGH, receptor binding dose not confer receptor signal activations. When either helices a or d of gfGH was maintained with other helices replaced by their gfPRL counterparts, both receptor binding and hence gene activation activities are reduced. In mutants with helices b and c in gfGH maintained, containing the gfGH middle section, and helices a and d swapped with gfPRL, the had reduced RRA activities but the promoter activation activities retained. In conclusion, as in the case of human GH, the gfGH molecule possesses two functional sites: one of them is composed of discontinuous epitopes located on the target regions of this study and is for receptor binding; another site is located on the middle section of the molecule that helices a and d are not involved, and it is for activation of GH receptor and intracellular signals.

The effects of the members of growth hormone family knockdown in zebrafish development

Growth hormone (GH), prolactin (PRL), and somatolactin (SL) are members of GH/PRL superfamily. These hormones are involved in the regulation of an array of physiological processes, including growth, lactation, and osmoregulation. While recent evidence has shown the GH, PRL, and SL gene transcripts and protein products are expressed during early zebrafish development, their functions at this time of embryogenesis remain unknown. In the current study, antisense morpholino oligonucleotide (MO) inhibition of gh, prl, and sl gene translation was used to examine the effects of gene knockdown on hormone function in zebrafish development. We observed that PRL, SLalpha and SLbeta MO treatment all affected development. PRL MO-treated embryos showed defects in gas bladder inflation, reduced head and eye size, shorter body length and fewer melanophores than untreated controls, whereas SLalpha and SLbeta MO-treated embryos were only defective in gas bladder inflation, GH MO-inhibition of GH specific translation did not lead to any discernable morphological changes within 10 days post fertilization (dpf). The effects of PRL knockdown were further verified using a second PRL morpholino antisense and by a rescue experiment with in vitro transcribed prl mRNA containing 5 nucleotide mismatch within the PRL-MO binding region. These results provide the first evidence that members of the GH/PRL superfamily play a role in proper development of various structures including the head, eyes, melanophores and the gas bladder in zebrafish.

The rat prolactin gene family locus: species-specific gene family expansion

In the rat there is a large family of paralogous genes related to prolactin (PRL). Members of the PRL family are expressed in cell- and temporal-specific patterns in the anterior pituitary, uterus, and placenta. An overriding feature of the PRL family is its association with pregnancy. In this investigation, we used information derived from the public rat genome database as a tool for identifying new members of the rat PRL family. The entire rat PRL gene family locus spans approximately 1.7 megabases (Mb) on Chromosome 17. Genes possessed either 5- or 6-exon organization patterns. We provide information on three newly identified genes orthologous to previously identified members of the mouse PRL gene family [placental lactogen-Ialpha (PL-Ialpha), PL-Ibeta, and proliferin (PLF)] and a new member of the PRL family, termed PRL-like protein-P (PLP-P). Information is also presented on the existence of multiple PLP-M transcripts, which are generated by alternative splicing. Expansion of the PRL family has occurred independently in rodents versus the cow and does not exist in the human and dog. Elucidation of the rat PRL gene family locus provides tools for studying the genetics and biology of the rat PRL family and new insights into species-specific gene family expansion.

The dawn and evolution of hormones in the adenohypophysis

The adenohypophysial hormones have been believed to have evolved from several ancestral genes by duplication followed by evolutionary divergence. To understand the origin and evolution of the endocrine systems in vertebrates, we have characterized adenohypophysial hormones in an agnathan, the sea lamprey Petromyzon marinus. In gnathostomes, adrenocorticotropin (ACTH) and melanotropin (MSH) together with beta-endorphins (beta-END) are encoded in a single gene, designated as proopiomelanocortin (POMC), however in sea lamprey, ACTH and MSH are encoded in two distinct genes, proopoicortin (POC) gene and proopiomelanotropin (POM) gene, respectively. The POC and POM genes are expressed specifically in the rostral pars distalis (RPD) and the pars intermedia (PI), respectively. Consequently, the final products from both tissues are the same in all vertebrates, i.e., ACTH from the PD and MSH from the PI. The POMC gene might have been established in the early stages of invertebrate evolution by internal gene duplication of the MSH domains. The ancestral gene might be then inherited in lobe-finned fish and tetrapods, while internal duplication and deletion of MSH domains as well as duplication of whole POMC gene took place in lamprey and gnathostome fish. Sea lamprey growth hormone (GH) is expressed in the cells of the dorsal half of the proximal pars distalis (PPD) and stimulates the expression of an insulin-like growth factor (IGF) gene in the liver as in other vertebrates. Its gene consists of 5 exons and 4 introns spanning 13.6 kb, which is the largest gene among known GH genes. GH appears to be the only member of the GH family in the sea lamprey, which suggests that GH is the ancestral hormone of the GH family that originated first in the molecular evolution of the GH family in vertebrates and later, probably during the early evolution of gnathostomes. The other member of the gene family, PRL and SL, appeared by gene duplication. A beta-chain cDNA belonging to the gonadotropin (GTH) and thyrotropin (TSH) family was cloned. It is expressed in cells of the ventral half of PPD. Since the expression of this gene is stimulated by lamprey gonadotropin-releasing hormone, it was assigned to be a GTHbeta. This GTHbeta is far removed from beta-subunits of LH, FSH, and TSH in an unrooted tree derived from phylogenetic analysis, and takes a position as an out group, suggesting that lampreys have a single GTH gene, which duplicated after the agnathans and prior to the evolution of gnathostomes to give rise to LH and FSH.

Evolution of the mammalian placenta revealed by phylogenetic analysis

The placenta is essential for the success of therian mammalian reproduction. Intense selective pressure has shaped changes in placental anatomy and function during mammalian cladogenesis. Here we challenge the view that the hemochorial placenta is a derived feature in haplorhine primates. Using phylogenetic and statistical analyses of molecular and morphological data, we demonstrate that the ancestral eutherian mammalian placenta had the distinctive features of (i) hemochorial placental interface, (ii) a discoid shape, and (iii) a labyrinthine maternofetal interdigitation. These results reveal that the first eutherians had a deeply invasive placenta and imply that the major role of the placenta in sustaining pregnancy and promoting gestational development existed throughout the eutherian lineage that descended to humans from the last common ancestor of placental mammals. The ancestral state reconstructions demonstrate both clade-specific patterns of placentation and specific cases of convergent evolution within individual eutherian clades. Determining the mammalian pattern of change in placental morphology is important for understanding the evolutionary pressures faced by these lineages. The effects of selection pressures on the efficiency of placentation may stem from changes in nutritional demand, gestational length, number of embryos per pregnancy, uterine shape, and maternal body constitution. The influence of these factors on placental development needs further investigation.

Massspectrometrical analysis of recombinant human growth hormone Norditropin® reveals amino acid exchange at M14_V14 rhGH

Recombinant human growth hormone (rhGH) is used for the treatment of several disorders. Structural integrity of rhGH is of critical importance for its clinical use and modifications thereof may act as markers in situations such as rhGH doping, as illegal rhGH-abuse in sports is of increasing interest. In the current study we investigated homogeneity of Norditropin, a recombinant human growth hormone frequently used in medicine, expressed in E. coli, strain MC1061. The most recent proteomics technologies including 2-DE, MALDI-MS followed by MALDI-MS/MS and LC-MS followed by LC-MS/MS were used for the characterisation of rhGH. MALDI-TOF-TOF and electrospray LC-MS analysis revealed one major protein with an average molecular mass of 22 126.0 Da and some additional minor components. Electrospray LC-MS/MS of the enzymatically digested Norditropin sample showed deamidation of N(12)N(149) and N(159), oxidation of M(14), M(125) and M(170) and one amino acid exchange V(14) for M(14) present in <1% of Norditropin. While deamidation and oxidation may be due to technical reasons, the single amino acid exchange may reflect infidelity of translation rather than codon usage and copy editing by E. coli.