Molecular cloning, tissue distribution, and expression of the prolactin receptor during various reproductive states in Meleagris gallopavo

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.

The Photoperiod-Driven Cyclical Secretion of Pineal Melatonin Regulates Seasonal Reproduction in Geese (Anser cygnoides)

The photoperiod is the predominant environmental factor that governs seasonal reproduction in animals; however, the underlying molecular regulatory mechanism has yet to be fully elucidated. Herein, Yangzhou geese (Anser cygnoides) were selected at the spring equinox (SE), summer solstice (SS), autumn equinox (AE), and winter solstice (WS), and the regulation of seasonal reproduction via the light-driven cyclical secretion of pineal melatonin was investigated. We show that there were seasonal variations in the laying rate and GSI, while the ovarian area decreased 1.5-fold from the SS to the AE. Moreover, not only did the weight and volume of the pineal gland increase with a shortened photoperiod, but the secretory activity was also enhanced. Notably, tissue distribution further revealed seasonal oscillations in melatonin receptors (Mtnrs) in the pineal gland and the hypothalamus-pituitary-gonadal (HPG) axis. The immunohistochemical staining indicated higher Mtnr levels due to the shortened photoperiod. Furthermore, the upregulation of aralkylamine N-acetyltransferase (Aanat) was observed from the SS to the AE, concurrently resulting in a downregulation of the gonadotrophin-releasing hormone (GnRH) and gonadotropins (GtHs). This trend was also evident in the secretion of hormones. These data indicate that melatonin secretion during specific seasons is indicative of alterations in the photoperiod, thereby allowing for insight into the neuroendocrine regulation of reproduction via an intrinsic molecular depiction of external photoperiodic variations.

Molecular characterisation and expression profile of the PRLR gene during goose ovarian follicle development

1. Although PRL-PRLR signalling plays important roles in regulating avian reproduction, there is a paucity of information regarding the functional significance of PRLR in goose ovarian follicle development.2. The full-length 2,496 bp coding sequence of PRLR was obtained from Sichuan White goose (Anser cygnoides) for the first time and was seen to encode a polypeptide containing 831 amino acids. Goose PRLR shares similar sequence characteristics and conserved functional domains to other avian species and was phylogenetically clustered into the avian clade.3. The qPCR results suggested that the mRNA levels of PRLR significantly increased in primary follicles during weeks 3 to 4 of age and were higher in secondary- than in primordial follicles at week 5 post-hatching, which suggested that the PRLR-mediated signalling could be involved in regulation of early folliculogenesis.4. The PRLR mRNA was expressed at the highest levels in the prehierarchical 8-10 mm granulosa layers throughout goose ovarian follicle development, indicating a role for PRLR in the process of follicle selection.5. PRLR mRNA was differentially expressed in the three cohorts of in vitro cultured granulosa cells harvested from different sized goose ovarian follicles, which suggested that PRLR was involved in regulating granulosa cell functions depending on the stage of follicle development. These data provide novel insights into the role of PRLR during goose ovarian follicle development, although the underlying mechanisms await further investigations.

Evidence for the Existence of Two Prolactin Isoforms in the Developing Pituitary Gland of the Goose (Anser cygnoides)

Compared to Galliformes such as chicken and turkey, very little is known about the existence and expression of isoforms of prolactin (PRL) in the pituitary glands of Anseriformes. In this study, by generating a rabbit-anti-goose (Anser cygnoides) PRL polyclonal antibody, we analysed the expression patterns of goose PRL isoforms in the embryonic and post-hatch development of the pituitary gland. Our results showed that two immunoreactive bands with molecular weights of about 23 and 26 kDa were detected using the Western blot technique, corresponding to the non-glycosylated (NG-) and the glycosylated (G-) isoform of PRL, respectively. The protein levels of the total PRL in a goose increased gradually from the embryonic day (ED) 22 to the post-hatch day (PD) 28, with a non-significant decrease on PD6. Furthermore, the percentage of G-PRL in the pituitary gland of the goose fluctuated from about 30.3% to 54.7% throughout the embryonic and post-hatch development. At the mRNA level, the expression of PRL increased steadily during the development and reached the highest levels on PD12, but later showed a non-significant decrease on PD28. The inconsistent expression patterns between the PRL mRNA and protein during the stages from PD6 to PD28 indicated that the PRL gene expression involves both transcriptional and post-translational regulation. Taken together, our data unequivocally demonstrated the existence of NG- and G-PRL in the pituitary gland of a goose and that the expression of the total PRL as well as the percentage of G-PRL significantly changed during embryonic and post-hatch development, indicating that the versatile biological functions of PRL during the ontogenesis of a goose could be closely related to changes in both its total expression and the degree of glycosylation in the pituitary gland.

Prolactin and prolactin receptor expression in the HPG axis and crop during parental care in both sexes of a biparental bird (Columba livia)

During breeding, multiple circulating hormones, including prolactin, facilitate reproductive transitions in species that exhibit parental care. Prolactin underlies parental behaviors and related physiological changes across many vertebrates, including birds and mammals. While circulating prolactin levels often fluctuate across breeding, less is known about how relevant target tissues vary in their prolactin responsiveness via prolactin receptor (PRLR) expression. Recent studies have also investigated prolactin (PRL) gene expression outside of the pituitary (i.e., extra-pituitary PRL), but how PRL gene expression varies during parental care in non-pituitary tissue (e.g., hypothalamus, gonads) remains largely unknown. Further, it is unclear if and how tissue-specific PRL and PRLR vary between the sexes during biparental care. To address this, we measured PRL and PRLR gene expression in tissues relevant to parental care, the endocrine reproductive hypothalamic-pituitary- gonadal (HPG) axis and the crop (a tissue with a similar function as the mammalian mammary gland), across various reproductive stages in both sexes of a biparental bird, the rock dove (Columba livia). We also assessed how these genes responded to changes in offspring presence by adding chicks mid-incubation, simulating an early hatch when prolactin levels were still moderately low. We found that pituitary PRL expression showed similar increases as plasma prolactin levels, and detected extra-pituitary PRL in the hypothalamus, gonads and crop. Hypothalamic and gonadal PRLR expression also changed as birds began incubation. Crop PRLR expression correlated with plasma prolactin, peaking when chicks hatched. In response to replacing eggs with a novel chick mid-incubation, hypothalamic and gonadal PRL and PRLR gene expression differed significantly compared to mid-incubation controls, even when plasma prolactin levels did not differ. We also found sex differences in PRL and PRLR that suggest gene expression may allow males to compensate for lower levels in prolactin by upregulating PRLR in all tissues. Overall, this study advances our understanding of how tissue-specific changes in responsiveness to parental hormones may differ across key reproductive transitions, in response to offspring cues, and between the sexes.

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.

Central prolactin receptor distribution and pSTAT5 activation patterns in breeding and non-breeding zebra finches (Taeniopygia guttata)

The hormone prolactin has many diverse functions across taxa such as osmoregulation, metabolism, and reproductive behavior. In ring doves, central prolactin action is important for parental care and feeding behavior. However, there is a considerable lack of information on the distribution of the prolactin receptor (PRLR) in the avian CNS to test the hypothesis that prolactin mediates these and other functions in other birds. In order to advance this research, we collected brains from breeding and non-breeding zebra finches to map the PRLR distribution using immunohistochemistry. We found PRLRs are distributed widely across the brain, both in hypothalamic sites known to regulate parental care and feeding, but also in many non-hypothalamic sites, including the tectofugal visual pathway, song system regions, reward associated areas, and pallium. This raises the possibility that prolactin has other functions throughout the brain that are not necessarily related to feeding or parental care. In addition, we also stained brains for pSTAT5, a transcription factor which is expressed when the PRLR is activated and is used as a marker for PRLR activity. We found several notable differences in pSTAT5 activity due to the breeding state of the animal, in both directions, further supporting the hypothesis that prolactin has many diverse functions in the brain both within and outside times of breeding. Together, this study represents the first essential step to inform the design of causative studies which manipulate PRLR-expressing cells to test their role in a wide variety of behaviors and other physiological functions.

Seasonal differences in the transcriptome profile of the Zhedong white goose (Anser cygnoides) pituitary gland

In animals, the adaptation to breed at the time of greatest survival of the young is known as seasonal reproduction. This is mainly controlled by the photoperiod, which stimulates the hypothalamic-pituitary-gonadal axis and starts the breeding season. Herein, we have determined the seasonal changes in gene expression patterns of Zhedong white geese pituitary glands under a natural photoperiodism, conducted at autumn equinox (AE), winter solstice (WS), spring equinox (SE), and summer solstice (SS). Pairwise comparisons of WS vs. AE, SE vs. WS, SS vs. SE, and AE vs. SS resulted in 1,139, 33, 704, and 3,503 differently expressed genes, respectively. When compared with SS, AE showed downregulation of genes, such as vasoactive intestinal peptide receptor, prolactin receptor, and thyroid hormone receptor beta, whereas gonadotropin-releasing hormone II receptor was upregulated, indicating that these genes may be responsible for the transition from cessation to egg laying. In addition, the expression levels of 5 transcription factors (POU1F1, Pitx2, NR5A1, NR4A2, and SREBF2) and 6 circadian clock-associated genes (Clock, Per2, ARNTL2, Eya3, Dio2, and NPAS2) also changed seasonally. Gene Ontology term and Kyoto Encyclopedia of Genes and Genomes enrichment analysis revealed that “response to oxidative stress” and steroid biosynthesis pathway also participate in regulating the reproduction seasonality of geese. Overall, these results contribute to the identification of genes involved in seasonal reproduction, enabling a better understanding of the molecular mechanism underlying seasonal reproduction of geese.

Integrative analysis of transcriptomic data related to the liver of laying hens: from physiological basics to newly identified functions

Background

At sexual maturity, the liver of laying hens undergoes many metabolic changes to support vitellogenesis. In published transcriptomic approaches, hundreds of genes were reported to be overexpressed in laying hens and functional gene annotation using gene ontology tools have essentially revealed an enrichment in lipid and protein metabolisms. We reanalyzed some data from a previously published article comparing 38-week old versus 10-week old hens to give a more integrative view of the functions stimulated in the liver at sexual maturity and to move beyond current physiological knowledge. Functions were defined based on information available in Uniprot database and published literature.

Results

Of the 516 genes previously shown to be overexpressed in the liver of laying hens, 475 were intracellular (1.23–50.72 fold changes), while only 36 were predicted to be secreted (1.35–66.93 fold changes) and 5 had no related information on their cellular location. Besides lipogenesis and protein metabolism, we demonstrated that the liver of laying hens overexpresses several clock genes (which supports the circadian control of liver metabolic functions) and was likely to be involved in a liver/brain/liver circuit (neurotransmitter transport), in thyroid and steroid hormones metabolisms. Many genes were associated with anatomical structure development, organ homeostasis but also regulation of blood pressure. As expected, several secreted proteins are incorporated in yolky follicles but we also evidenced that some proteins are likely participating in fertilization (ZP1, MFGE8, LINC00954, OVOCH1) and in thyroid hormone maturation (CPQ). We also proposed that secreted proteins (PHOSPHO1, FGF23, BMP7 but also vitamin-binding proteins) may contribute to the development of peripheral organs including the formation of medullar bones to provide labile calcium for eggshell formation. Thirteen genes are uniquely found in chicken/bird but not in human species, which strengthens that some of these genes may be specifically related to avian reproduction.

Conclusions

This study gives additional hypotheses on some molecular actors and mechanisms that are involved in basic physiological function of the liver at sexual maturity of hen. It also revealed some additional functions that accompany reproductive capacities of laying hens, and that are usually underestimated when using classical gene ontology approaches.

Effects of nonglycosylated and glycosylated prolactin on basal and gonadotropin-stimulated steroidogenesis in chicken ovarian follicles

In galliformes, the circulating isoform of prolactin (PRL) significantly changes during different reproductive states. However, the role of the major isoform (glycosylated PRL [G-PRL]) in ovarian steroidogenesis is unknown. The present study aimed to compare the effects of nonglycosylated (NG-) and G-PRL on basal and gonadotropin-stimulated estradiol (E₂) and progesterone (P₄) production in granulosa cells or follicular walls of chicken of different size class follicles. In the initial experiment, granulosa cells of preovulatory F3-F1 and prehierarchical 6- to 8-mm follicles were incubated for 24 h with different concentrations of NG- or G-PRL (0, 1, 10, 100, or 1,000 ng/mL). In the subsequent experiments, these categorized granulosa cells and follicular walls of prehierarchical 4-6, 2-4, and <2-mm follicles were incubated for 24 h in the absence and presence of 10-ng/mL FSH or LH, or in combination with different concentrations of NG- or G-PRL (10, 100, or 1,000 ng/mL). We observed that lower levels of NG-PRL induced (P < 0.05) E₂ and P₄ secretion in granulosa cells of either preovulatory or prehierarchical follicles, but at higher levels, this effect was reduced. In contrast, G-PRL promoted (P < 0.05) basal E₂ and P₄ secretion in preovulatory granulosa cells but was inhibitory (P < 0.05) in prehierarchical granulosa cells. Results obtained by real-time quantitative PCR (qPCR) demonstrated that these effects were mediated through modulation of the expression of StAR, CYP11A1, CYP19A1, and 3β-HSD. Furthermore, G-PRL was less potent than NG-PRL in inhibiting FSH- or LH-stimulated E₂ and P₄ production in granulosa cells of preovulatory follicles, whereas NG-PRL enhanced (P < 0.05) but G-PRL reduced (P < 0.05) FSH-induced P₄ production in those of prehierarchical follicles. In follicular walls from each group of prehierarchical 4-6, 2-4, and <2-mm follicles, NG- and G-PRL had both stimulatory and inhibitory influences on the actions of FSH on E₂ and P₄ secretion, but both suppressed (P < 0.05) LH-induced E₂ and P₄ secretion except for the synergistic effects of LH and G-PRL on P₄ secretion by follicular walls of the follicles of 4-6 mm. Taken together, these results suggest that both NG- and G-PRL are biologically active in regulating basal and gonadotropin-stimulated E₂ and P₄ production in chicken ovarian follicles. However, their effects are different depending on the concentration, the type of gonadotropin (FSH or LH), and the stage of follicle development.

Regulatory Mechanisms Underlying the Expression of Prolactin Receptor in Chicken Granulosa Cells

Prolactin (PRL) has both pro- and anti-gonadal roles in the regulation of avian ovarian functions through its interaction with the receptor (PRLR). However, neither the pattern of expression of PRLR nor its regulatory mechanisms during follicle development have been clearly defined. The objective of the present study was to investigate mechanisms of PRLR expression in chicken granulosa cells. Levels of PRLR transcript were highest in the stroma and walls of follicles < 2 mm in diameter and progressively declined with the maturation of follicles. In preovulatory follicles, PRLR was expressed at higher levels in granulosa than theca layers. FSH exerted the greatest stimulatory effect on PRLR and StAR expression in cultured granulosa cells of the 6–8 mm follicles but this effect declined as follicles matured to F1. In contrast, LH did not alter the expression of PRLR in granulosa cells of all follicular classes but increased levels of StAR in F2 and F1 granulosa cells. Both non-glycosylated- (NG-) and glycosylated- (G-) PRL upregulated basal PRLR expression in granulosa cells of the 6–8 mm, F3 or F1 follicles but had little effect in F2 follicles. Furthermore, FSH-stimulated PRLR expression was reduced by the addition of either isoform of PRL especially in F2 granulosa cells. These results indicate that PRLR is differentially distributed and regulated by FSH or PRL variants independently or in combination in the follicular hierarchy. By using activators and inhibitors, we further demonstrated that multiple signaling pathways, including PKA, PKC, PI3K, mTOR and AMPK, are not only directly involved in, but they can also converge to modulate ERK2 activity to regulate FSH-mediated PRLR and StAR expression in undifferentiated granulosa cells. These data provide new insights into the regulatory mechanisms controlling the expression of PRLR in granulosa cells.

Neuroendocrine Control of Broodiness

In the majority of vertebrates, survival of offspring to sexual maturation is important for increasing population size, and parental investment in the young is important for reproductive success. Consequently, parental care is critical for the survival of offspring in many species, and many vertebrates have adapted this behavior to their social and ecological environments. Parental care is defined as any behavior that is performed in association with one's offspring (Rosenblatt, Mayer, Siegel. Maternal behavior among nonprimate mammals. In: Adler, Pfaff, Goy, editors. Handbook of behavioral neurobiology. New York: Plenum; 1985. p. 229-98) and is well characterized in mammals and birds. In birds (class Aves), this is due to the high level of diversity across species. Parental behavior in birds protects the young from intruders, and generally involves nest building, incubation, and broody behavior which protect their young from an intruder, and the offspring are reared to independence. Broodiness is complexly regulated by the central nervous system and is associated with multiple hormones and neurotransmitters produced by the hypothalamus and pituitary gland. The mechanism of this behavior has been extensively characterized in domestic chicken (Gallus domesticus), turkey (Meleagris gallopavo), and pigeons and doves (family Columbidae). This chapter summarizes broodiness in birds from a physiology, genetics, and molecular biology perspective.

Expression and regulation of prolactin-like protein messenger RNA in undifferentiated chicken granulosa cells

Prolactin-like protein (PRL-L; LOC417800) is a homolog of PRL in non-mammalian vertebrates and can act as a functional ligand of PRL receptor (PRLR). Despite its widespread expression in extrapituitary tissues, mechanisms of regulation of PRL-L in the chicken ovary remain unknown. In this study, we first examined PRL-L expression in chicken ovarian developing follicles. PRL-L transcript levels were highest (P<0.05) in follicular walls of <2mm follicles and progressively declined during follicle maturation. Undifferentiated granulosa cells of 6-8mm follicles had higher (P<0.05) PRL-L mRNA levels than differentiated granulosa cells of F3, F2 or F1 follicles. In cultured undifferentiated granulosa cells, levels of PRL-L transcript were increased (P<0.05) by follicle stimulating hormone (FSH) treatment while were not altered by the addition of luteinizing hormone (LH). In addition, 10ng/ml non-glycosylated (NG-) and 1ng/ml glycosylated (G-) PRL increased (P<0.05) but at higher levels (100 or 1000ng/ml) both showed no effects on PRL-L expression. Furthermore, 100ng/ml NG-PRL enhanced (P<0.05) FSH-induced PRL-L expression, whereas the effects of G-PRL were not significant. These results suggest that PRL-L mRNA is differentially expressed in the follicular hierarchy and its high abundance in undifferentiated granulosa cells is under the regulation of FSH or PRL variants independently or in combination. Moreover, in undifferentiated granulosa cells we also provide evidence for a positive role for PKA, PKC and PI3K signaling while a negative role for ERK2 in mediating FSH stimulation of PRL-L transcription.

The role of the prolactin/vasoinhibin axis in rheumatoid arthritis: an integrative overview

Rheumatoid arthritis (RA) is a chronic, autoimmune, inflammatory disease destroying articular cartilage and bone. The female preponderance and the influence of reproductive states in RA have long linked this disease to sexually dimorphic, reproductive hormones such as prolactin (PRL). PRL has immune-enhancing properties and increases in the circulation of some patients with RA. However, PRL also suppresses the immune system, stimulates the formation and survival of joint tissues, acquires antiangiogenic properties upon its cleavage to vasoinhibins, and protects against joint destruction and inflammation in the adjuvant-induced model of RA. This review addresses risk factors for RA linked to PRL, the effects of PRL and vasoinhibins on joint tissues, blood vessels, and immune cells, and the clinical and experimental data associating PRL with RA. This information provides important insights into the pathophysiology of RA and highlights protective actions of the PRL/vasoinhibin axis that could lead to therapeutic benefits.

Expression of Prolactin Receptor on the Surface of Quail Spermatozoa

Prolactin receptor (PRLR) is expressed in a wide variety of tissues and mediates diverse biological actions of prolactin (PRL). In mammals, PRL signaling is thought to be involved not only in the process of spermatogenesis and steroidogenesis in the testis, but also in the survival of ejaculated sperm. In avian species, although the expression of PRLR with several variants in the testis was reported, the role of PRL in testicular function is still unclear. The aim of this study was to examine the expression of PRLR in the testis and mature sperm in quail. It is revealed that PRLR was mainly localized in the round- and elongated-spermatid by immunohistochemical analysis on the testis suggesting that PRL signaling may participate in the spermatogenesis. Western blot analysis confirmed the presence of PRLR in the plasma membrane of the ejaculated sperm (SPML), whereas the size of PRLR in the sperm was smaller than that in the hypothalamus. Moreover, PRLR was detected on the surface of the midpiece and flagellum of sperm by immunostaining. To evaluate the functionality of the sperm PRLR, the dot blot assay was performed to test the binding of pituitary PRL to PRLR in the SPML, and resulted in the detection of specific binding of PRL to the component of SPML, most likely to sperm PRLR. Furthermore, when the ejaculates were incubated with pituitary PRL to investigate the role of PRL on the sperm, the occurrence of spontaneous acrosome reaction was significantly decreased. In addition, the expression of PRL on the surface of utero-vaginal junction of oviduct was detected by immunohistochemistry. These results may suggest a novel system that the interaction between oviductal PRL and sperm PRLR is involved in the maintenance of the fertilizability of the spermatozoa through the prevention of the spontaneous acrosome reaction in Japanese quail.

Effect of breeding stage and photoperiod on gonadal and serotonergic axes in domestic ganders

Reduction in reproductive potential of ganders with progress in seasonal breeding is a known problem in commercial geese production. The role of changes in hypothalamic-pituitary-gondal axis and testis functions in this process is not clear. This article presents studies on the hypothalamic (GnRH-I, vasoactive intestinal peptide), pituitary (LHβ, prolactin [PRL], PRL receptor [PRLR]), testis (PRLR) axis messenger RNA (mRNA) expression during different stages of the breeding period and photoperiodic conditions. Testis mass; histologic and functional (testosterone [T]) parameters; and plasma concentrations of T, LH, and PRL were evaluated. We collected (six times) samples from 2-year-old ganders (n = 48) maintained in short day (10L:14D) during the period from November to July. Moreover, in the peak of sexual activity (March), an additional group was on exposure (6 weeks) to long day (LD; 16L:8D). During the first half of reproduction (January, March; photosensitive period), GnRH-I (1.9 vs. 0.3 relative quantity [RQ]) and LHβ (3.0 vs. 0.7 RQ) mRNA transcript expression and concentrations of T (1.9-2.9 vs. 0.3 ng/mL), LH (13.6-7.4 vs. 0.7 ng/mL) were found to be higher (P < 0.05) than at the end of breeding (July). With progress in breeding, marked elevation (P < 0.05) in PRL (22.0-387.1 ng/mL) concentration related to similar changes in vasoactive intestinal peptide (0.9-3.0 RQ) and PRL mRNA abundance (1.3-11.5 RQ; May, July) was observed. However, testis PRLR mRNA increased (P < 0.05) only at the end of reproduction (1.2 RQ) compared to the peak of sexual activity (0.4 RQ; March). Furthermore, changes in mRNA transcript expression of the lactotrophic axis were accompanied with reduction of testis weight (left: 11.1-5.8 g), spermatogenesis (spermatogenic index: 5.4-3.0), and steroidogenesis (T: 24.8-1.3 ng/g testis), which may suggest their pivotal inhibitory modulation role in the regression of seasonal reproductive activity in ganders. The LD conditions (similar to spring-summer) resulted in earlier peripheral changes in T (0.9 vs. 1.8 ng/mL), LH (1.1 vs. 3.8 ng/mL), and PRL (296.1 vs. 161.2 ng/mL) concentrations than in short day, and this may be related to the advance in the timing of the sexual activity failure observed under natural light regimes. The lack of differences in gonadal and lactotrophic axis mRNA expression after LD treatment suggested a regulation based on the posttranslational mechanisms or modification of transcript or protein.

Arthritis and prolactin: a phylogenetic viewpoint

Arthritic disorders are family of diseases that have existed since vertebrate life began. Their etiology is multifactorial with genetic, environmental, and gender factors driving chronic joint inflammation. Prolactin is a sexually dimorphic hormone in mammals that can act to both promote and ameliorate rheumatic diseases. It is found in all vertebrate groups where it exerts a wide diversity of actions. This review briefly addresses the presence and features of arthritic diseases in vertebrates, the effects of PRL on joint tissues and immune cells, and whether PRL actions could have contributed to the ubiquity of arthritis in nature. This comparative approach highlights the value of PRL as a biologically conserved factor influencing the development and progression of arthritis.

Reproductive actions of prolactin mediated through short and long receptor isoforms

Prolactin (PRL) is a polypeptide hormone with a wide range of physiological functions, and is critical for female reproduction. PRL exerts its action by binding to membrane bound receptor isoforms broadly classified as the long form and the short form receptors. Both receptor isoforms are highly expressed in the ovary as well as in the uterus. Although signaling through the long form is believed to be more predominant, it remains unclear whether activation of this isoform alone is sufficient to support reproductive functions or whether both types of receptor are required. The generation of transgenic mice selectively expressing either the short or the long form of PRL receptor has provided insight into the differential signaling mechanisms and physiological functions of these receptors. This review describes the essential finding that both long and short receptor isoforms are crucial for ovarian functions and female fertility, and highlights novel mechanisms of action for these receptors.

Molecular characterization of prolactin receptor (cPRLR) gene in chickens: gene structure, tissue expression, promoter analysis, and its interaction with chicken prolactin (cPRL) and prolactin-like protein (cPRL-L)

In this study, gene structure, tissue expression, and promoter usage of prolactin receptor (PRLR) and its interaction with prolactin (PRL) and the newly identified prolactin-like protein (PRL-L) were investigated in chickens. The results showed that (1) PRLR gene was found to consist of at least 25 exons by 5'-RACE and RT-PCR assays; (2) multiple PRLR 5'-UTR sequences different in exon composition were isolated from chicken liver or intestine by 5'-RACE and could be subdivided into type I and type II transcripts according to the first exon used (exon 1G or exon 1A); (3) PRLR Type I transcripts with exon 1G were detected to be predominantly expressed in adult kidney and small intestine by RT-PCR, implying their expression is likely controlled by a tissue-specific promoter (P1). By contrast, PRLR type II transcripts containing exon 1A are widely expressed in adult and embryonic tissues examined and their expression is controlled by a generic promoter (P2) near exon 1A, which was demonstrated to display promoter activities in cultured DF-1, HEK293 and LoVo cells by the dual-luciferase reporter assay; (4) Using a 5×STAT5-luciferase reporter system, cPRLR expressed in HepG2 cells was shown to be activated by recombinant cPRL and cPRL-L via interaction with PRLR membrane-proximal ligand-binding domain, suggesting that like cPRL, cPRL-L is also a functional ligand of cPRLR. Collectively, characterization of cPRLR gene helps to elucidate the roles of PRLR and its ligands in birds and provides insights into the regulatory mechanisms of PRLR expression conserved in birds and mammals.

Changes in post-translational modifications of prolactin during development and reproductive cycles in the chicken

Changes in proportion of glycosylated prolactin in the anterior pituitary glands of chickens were assessed using one- and two-dimensional western blotting analysis during the perihatch stage of embryos and reproductive cycles. Multiple isoforms of prolactin were detected by one-dimensional analysis and glycosylated (G) and non-glycosylated (NG) isoforms were identified by N-glycosidase and neuraminidase treatment. Increases of ratio of G to NG isoforms were observed in both embryonic stages and reproductive cycles by the one-dimensional analysis. Although a similar tendency of increase of proportion of G prolactin was obtained, different values of proportion were observed between one-dimensional and two-dimensional analysis. Since two-dimensional analysis may better resolve isoforms differing slightly in molecular size of G prolactin, the results from two-dimensional analysis may reflect the actual proportion of prolactin isoforms. Furthermore, isoforms differing in isoelectric points were detected after N-glycosidase and neuraminidase treatment. These results indicate that prolactin may also be additionally post-translationally modified such as by phosphorylation. Thus function and biological activity of prolactin were, at least in part, regulated by post-translational modification in the various physiological stages.

[Expression characteristics of prolactin gene in Eastern Zhejiang white geese]

This study was conducted to clone the prolactin gene (PRL) in Eastern Zhejiang White Geese and to investigate the PRL gene expression characteristics during egg-laying, out-of-lay and incubating periods by real time PCR. Comparisons were made respectively of concentration of prolactin mRNA in the hypothalamus, pituitary gland and ovary of the adult female geese at different reproductive periods. The result indicated that there were significant differences (P<0.05) in PRL mRNA expression between different reproductive periods of the geese. The lowest level of PRL expression was found in out-of-lay geese, higher in the egg-laying geese, and the highest in incubating geese. Furthermore, the analysis of PRL expression in different tissues indicated that the highest levels of PRL was expressed in the pituitary gland, followed in hypothalamus, and the least in ovary of the geese. There were significant difference (P<0.01) expression of PRL between the pituitary gland/hypothalamus and ovary of the geese, whereas no any difference was observed between the pituitary gland and hypothalamus (P>0.05). In summary, the PRL mRNA expression had variance in different reproductive periods of the geese.

Ontogenesis of the Expression of Prolactin Receptor Messenger Ribonucleic Acid During Late Embryogenesis in Turkeys and Chickens

Changes in circulating levels of prolactin (PRL) and tissue content of PRL receptor (PRLR) messenger RNA (mRNA) in the liver, pancreas, kidney, and gonads (testis/ovary) were measured in turkey and chicken embryos from embryonic day (ED) 21 or ED15, respectively, to 1 d after hatch by real-time PCR. There were no differences between the sexes in chickens or turkeys. Both species had very similar patterns of PRL release and expression of PRLR mRNA, and no major differences were observed between turkey or chicken embryos. Plasma levels of PRL increased from low levels during the last week of embryonic development and were at significantly higher levels (about 4-fold) by 1 d after hatch. Similarly, in all tissues the content of PRLR mRNA was minimal at the outset and increased to reach maxima about the time of hatch. In both species, the highest levels of transcript were observed in the kidney followed by the gonad, liver, and pancreas. The tissue content of PRLR was correlated (0.6 to 0.8 dependent on the tissue) to circulating levels of PRL, which suggested that PRL may be associated with an increase in its receptor number around the time of hatch. Because levels of PRL and tissue content of PRLR mRNA increased around the time of hatch, this suggests that these tissues may be targets for PRL and may be involved in the physiologic changes occurring in embryos around the time of hatching.

Development of a real-time (Q) PCR assay to measure variation in expression of prolactin receptor mRNA in the hypothalamus and pituitary gland during late embryogenesis in turkeys and chickens

Changes in levels of PRLR mRNA in the pituitary gland and hypothalamus of chickens and turkeys from embryonic day (ED) 15 and ED21 to 1 day post-hatch, respectively, were measured by real-time PCR. In both species, PRLR mRNA increased from low levels during the last week of ED to reach maxima at the peri-hatch period. Similarly, circulating levels of PRL also increased during this interval and were highly correlated with levels of the PRLR mRNA in both the pituitary gland and hypothalamus. This suggests that PRL was up-regulating its receptor. In support of this, stimulation of the turkey pituitary gland with VIP on ED24 resulted in a 4- and 3-fold increase in PRL and PRLR, respectively. Since VIP had no direct effect on the levels of PRLR transcript in the hypothalamus, it is likely that VIP is acting indirectly through increased PRL to up-regulate the number of receptors.

Prolactin and prolactin receptor expressions in a marine teleost, pufferfish Takifugu rubripes

To investigate the physiological significance of prolactin (PRL) in a marine teleost, pufferfish (or fugu), Takifugu rubripes, we cloned and characterized cDNAs encoding its PRL and PRL receptor (PRLR) from the pituitary and gills, respectively. The fugu PRL cDNA consisted of 995 bp and encoded a protein of 213 amino acids. The PRLR, consisting of 510 amino acids, contained a putative signal peptide, an extracellular domain with two pairs of cysteines, a WSXWS motif, a single transmembrane domain, and a cytoplasmic (intracellular) domain with box 1 and box 2 regions, all of which are characteristic of the cytokine receptor superfamily. Reverse transcription-PCR showed the expression of PRLR mRNA in osmoregulatory organs, such as gills, kidney, and intestine, whereas pufferfish PRL mRNA was detected only in the pituitary. Furthermore, in situ hybridization revealed the expression of pufferfish PRLR in branchial chloride cells, kidney tubule cells, and intestinal epithelia. The PRL-gene expression levels in the pituitary were about five times higher in 25%-diluted seawater than in full-strength seawater. These results suggest that fugu PRL regulates water and electrolyte balances through PRLR expressed in the osmoregulatory organs, as is the case with freshwater-adapted euryhaline species.

Expression of prolactin receptor mRNA in the abdominal gland of the newt Cynops ensicauda

To further the understanding that the structural development of the Cynops ensicauda abdominal gland and the synthesis of the pheromone silefrin in the gland are under the control of prolactin and androgen, we sought to demonstrate the presence of prolactin receptor (PRLR) mRNA in the gland. Firstly, PRLR cDNA was isolated from an abdominal gland cDNA library. A cDNA consisting of a 415-bp 5'-untranslated region, 1878-bp open reading frame and 175-bp 3'-untranslated region was obtained. The deduced amino acid sequence consisted of 626 amino acids with signal peptide and single transmembrane domain. By Northern blot analysis using partial C. ensicauda PRLR cDNA, two transcripts, of 3 and 10 kb, were detected for PRLR in the brain, liver, kidney, abdominal gland, oviduct and skin. RT-PCR coupled with Southern blot analysis showed that the PRLR gene was transcribed broadly in newt organs and revealed that PRLR mRNA levels in the abdominal gland were much higher in sexually developed newts than in the sexually undeveloped ones. By in situ hybridization, specific signals were detected in the epithelial cells of the abdominal gland of sexually developed newts, but much less in those of the sexually undeveloped ones.

Tissue distribution of prolactin receptor mRNA during late stage embryogenesis of the chick

Serum prolactin increases during late embryogenesis. In order to elucidate the function of prolactin at this period, tissue distribution of prolactin receptor mRNA was examined by RNase protection assay. The mRNA was detected strongly in the kidney, intestine, and allantoic membrane; weakly detected in the brain; but not detected in the liver. The expression levels of the prolactin receptor mRNA in the kidney, intestine, and allantoic membrane were retained at constant levels during later stages of embryogenesis (Days 17 and 19) and posthatch periods (2 and 28 d after hatching). These results suggest that prolactin is mainly involved in the osmoregulation during the later stage of embryogenesis and that the expression of prolactin receptor mRNA in the kidney, intestine, and allantoic membrane is regulated by a serum prolactin-independent manner.

Structure and tissue distribution of prolactin receptor mRNA in Japanese flounder (Paralichtys olivaceus): conserved and preferential expression in osmoregulatory organs

In diadromous and euryhaline teleosts, it has been established that prolactin (PRL) is a major hormone regulating the maintenance of water and electrolyte homeostasis by acting on its receptor (PRLR) expressed in the osmoregulatory organs. To investigate the major physiological role of PRL in a marine teleost, cDNA for the Japanese flounder (Paralichtys olivaceus) prolactin receptor (fPRLR) has been cloned and characterized. The predicted fPRLR is composed of 636 amino acids conserving common structural features, such as the WSXWS motif and box 1, that are observed in the members of the cytokine receptor superfamily. By Northern blot analysis, 3.5-kb transcripts for fPRLR were clearly detected in the gill, kidney, and intestine. By RNase protection assay, similarly high levels of mRNA expression were detected in these osmoregulatory organs and lower expression levels were seen in the brain for both males and females. Interestingly, a distinct expression level of fPRLR mRNA was observed in the testis, but not in the ovary. The present results suggest that PRL may play an important role in the control of water and electrolyte balance through PRLR expressed in the osmoregulatory organs in the marine teleost the Japanese flounder as well as in other teleosts. Furthermore, PRL may differentially regulate gonadal functions in males and females of Japanese flounder.

Cloning, characterization, and tissue distribution of prolactin receptor in the sea bream (Sparus aurata)

The prolactin receptor (PRLR) was cloned and its tissue distribution characterized in adults of the protandrous hermaphrodite marine teleost, the sea bream (Sparus aurata). An homologous cDNA probe for sea bream PRLR (sbPRLR) was obtained by RT-PCR using gill mRNA. This probe was used to screen intestine and kidney cDNA libraries from which two overlapping clones (1100 and 2425 bp, respectively) were obtained. These clones had 100% sequence identity in the overlapping region (893 bp) and were used to deduce the complete amino acid sequence of sbPRLR. The receptor spans 2640 bp and encodes a protein of 537 amino acids. Features characteristic of PRLR, two pairs of cysteines, WS box, hydrophobic transmembrane domain, box 1, and box 2, were identified and showed a high degree of sequence identity to PRLRs from other vertebrate species. SbPRLR is 29 and 32% identical to tilapia (Oreochromis niloticus) and goldfish (Carassius auratus) PRLRs, respectively. In the sea bream two PRLR transcripts of 2.8 and 3.2 kb were detected in the intestine, kidney, and gills and a single transcript of 2.8 kb was detected in skin and pituitary by Northern blot. Spermiating gonads (more than 95% male tissue; gonado-somatic index of 0.6) contained, in addition to the 2.8-kb transcript, three more transcripts of 1.9, 1.3, and 1.1 kb. RT-PCR, which is a far more sensitive method than Northern blot, detected PRLR mRNA in gills, intestine, brain, pituitary, kidney, liver, gonads, spleen, head-kidney, heart, muscle, and bone. Immunohistochemistry using specific polyclonal antibodies raised against an oligopeptide from the extracellular domain of sbPRLR detected PRLR in several epithelial tissues of juvenile sea bream, including the anterior gut, renal tubule, choroid membrane of the third ventricle, saccus vasculosus, branchial chloride cells, and branchial cartilage.

Molecular characterization of the prolactin receptor in two fish species, tilapia Oreochromis niloticus and rainbow trout, Oncorhynchus mykiss: A comparative approach

We present recent information on the molecular characterization of the prolactin receptor (PRL-R) in two teleost species, tilapia (Oreochromis niloticus) and rainbow trout (Oncorhynchus mykiss), in the perspective of improved understanding of the physiological differences in the control of osmoregulatory function between these two fish species. Although our interest will mainly focus on osmoregulatory organs, we will also discuss evidence of the presence of PRL-R in other tissues such as gonads and hematopoietic organs. The first fish PRL-R was characterized in tilapia. This receptor is similar to that of the long form of mammalian PRL-R, but the most conserved region (extracellular domain) has only 53% identity with mammalian PRL-R. A rainbow trout PRL-R cDNA has been also isolated and appeared very similar in structure to tilapia PRL-R. Expression of the PRL-R gene was studied by Northern blotting for various tissues from tilapia and trout, and a unique transcript size of 3.2-3.4 kb was observed in all tissues studied (including male and female gonads, skin, brain, spleen, head, kidney, and circulating lymphocytes). Osmoregulatory organs (gills, kidney, intestine) were the richest tissues. Using in situ hybridization, PRL-R transcripts were localized in gill chloride cells, both in trout and tilapia. Analysis of PRL-R transcript levels in gills, kidney, and intestine indicated the maintenance of a high level of expression during adaptation to a hyperosmotic environment. These results support PRL being a pleiotropic hormone in fish and suggest the presence of a unique PRL-R form in tilapia and in trout. Finally, characterization of hormone receptor binding has been carried out in both species using a radioreceptor assay (in tilapia) or surface plasmon resonance (SPR) technology (in trout). These studies indicated the presence of a stable hormone-receptor complex in tilapia, while PRL binds to its receptor through an unstable homodimeric complex in trout. Thus, the characteristics of PRL binding on its receptor appear to be significantly different in tilapia and trout. Whether such differences may lead to different signal transduction mechanisms and osmoregulatory actions of PRL in these two euryhaline species merits further investigation.Key words: prolactin receptor, genetic expression, hormone-receptor interaction, surface plasmon resonance, fish osmoregulation.

Newt prolactin and its involvement in reproduction

The amino acid sequence of newt (Cynops pyrrhogaster) prolactin deduced from the nucleotide sequence of its cDNA showed a relatively high homology with sequences of chicken and sea turtle prolactins as well as with those of anuran prolactins. Cynops prolactin receptor transcripts were detected in various tissues and organs, suggesting that prolactin plays multiple roles in urodeles. Urodele prolactin was purified from the pituitaries of C. pyrrhogaster. Antiserum against this prolactin was used for radioimmunoassay of plasma prolactin and immunoneutralization experiments. Endogenous prolactin was shown to induce migration to water, courtship behavior, and cessation of spermatocytogenesis in the Cynops newt. The hormone was found to be involved in the development of cloacal glands such as the lateral and abdominal glands, growth of the tail and Mauthner neurons, secretion of oviducal jelly, and enhanced synthesis of a female attracting pheromone (sodefrin), and responsiveness of the olfactory epithelium to sodefrin. In most of these cases, prolactin was found to act synergistically or antagonistically with sex steroids. We also discovered that hypersecretion of prolactin in the newts subjected to cold temperature was induced by hypothalamic stimulation rather than release from hypothalamic inhibition.Key words: prolactin, newts, reproduction.

The role of prolactin in the regulation of clutch size and onset of incubation behavior in the American kestrel

In most bird species, the timing of incubation onset may influence the degree of hatching asynchrony, which, together with variation in clutch size, affects reproductive success. In some domesticated species that usually show no hatching asynchrony, plasma prolactin concentrations in females rise with the onset of incubation and the end of laying, and this rise enhances incubation behavior and may terminate laying. To investigate whether a rise in prolactin during laying is involved in the regulation of clutch size and incubation onset in a species with hatching asynchrony, we measured plasma concentrations of immunoreactive prolactin (ir-prolactin) in laying American kestrels, Falco sparverius, and quantified clutch size and incubation behavior. In a separate study, we administered one of three concentrations of ovine prolactin (o-prolactin) via osmotic pumps implanted in females when egg 2 of a clutch was laid. ir-Prolactin concentrations during laying were higher in small than in large clutches and increased in parallel with the development of incubation behavior. o-Prolactin treatment enhanced incubation behavior, but did not affect clutch size, possibly because the manipulation was performed after clutch size had already been determined. Consistent with studies on domesticated species that show synchronous hatching, our results indicate that rising prolactin during laying enhances the expression of incubation behavior in a species that shows hatching asynchrony. Further studies are necessary to determine whether the relationship between prolactin and clutch size in the American kestrel is one of causation or of mere association.

Two novel first exons in the prolactin receptor gene are transcribed in a tissue-specific and sexual maturation-dependent manner to encode multiple 5'-truncated transcripts in the testis of the chicken

Cloning and sequencing of the chicken prolactin receptor (PRLR) gene segment from the transmembrane domain to the box 2 motif revealed the presence of the two testis-specific first exons, TSE-1 and TSE-2, encoding the unique 5'-end sequences of the reported and newly identified multiple 5'-truncated PRLR transcripts containing only the cytoplasmic domain in the testis. TSE-1 was located downstream of the exon encoding the transmembrane domain and TSE-2 presented downstream of the exon encoding the box 1 motif. These findings indicate that the box 1-containing 5'-truncated transcripts are generated by the utilization of TSE-1 as the first exon with distinct splicing donor sites to the box 1-containing exon, and that the utilization of TSE-2 as the first exon and its splicing to the box 2-containing exon results in the generation of the box 1-lacking transcript. Three transcription initiation sites for the box 1-containing 5'-truncated transcripts and two transcription initiation sites for the box 1-lacking transcript were detected by the RNase protection assays. Reverse transcription-polymerase chain reaction analysis showed that the expression levels of all these 5'-truncated PRLR transcripts are simultaneously increased during sexual maturation, accompanying the decrease of the amount of the canonical full-length transcript for PRLR.

Evidence for multiple prolactin receptor transcripts in the turkey

Multiple prolactin receptor (PRL-R) mRNA transcript isoforms have been identified in mammals, but there are conflicting reports concerning the number of avian PRL-R isoforms. We hypothesized that multiple turkey PRL-R transcript isoforms exist and that PRL-R mRNA abundance may be related to reproductive status. Two turkey PRL-R cDNA fragments were generated using reverse transcriptase polymerase chain reaction (RT-PCR) that displayed a high degree of similarity to mammalian and avian PRL-R. Northern blot analysis of poly A+ mRNA hybridized to a turkey PRL-R riboprobe revealed a 3.1-kb band in the liver, oviduct, and testes. Additional 1.5- and 10.7-kb transcripts were found in the liver and testes, respectively. Hybridization of the same Northern blot to a chicken PRL-R probe verified the presence of a 3.1-kb transcript in all three tissues. A Northern blot was used to examine turkey PRL-R transcript isoform expression in laying hens. A 3.1-kb band was found in the pineal, infundibulum, magnum, isthmus, kidney, and intestine. In addition, 10.7- and 7.3-kb bands were detected in the pineal, magnum, isthmus, and intestine. Turkey PRL-R transcript isoforms were also examined throughout the reproductive cycle. The 10.7-, 7.3-, and 3.1-kb isoforms were detected in the oviduct, intestine, and pineal during each reproductive state. Turkey PRL-R mRNA levels were also compared during the reproductive cycle. Turkey PRL-R mRNA levels were greatest in laying hen pineal glands (P<0.05) and in incubating hen oviducts. This study provides the first evidence for multiple PRL-R mRNA transcript isoforms in turkeys.

Quantification of prolactin messenger ribonucleic acid, pituitary content and plasma levels of prolactin, and detection of immunoreactive isoforms of prolactin in pituitaries from turkey embryos during ontogeny

The content of prolactin mRNA as well as total prolactin content and type of isoforms of prolactin were measured in single pituitary glands from turkey embryos and poults. Levels of mRNA and pituitary content of prolactin remained low until 5 days before hatching, while plasma concentrations remained low until 2 days before hatching. Levels of prolactin mRNA then increased until the day of hatch, stayed stable during the 3 first days of age, and significantly increased until 2 wk of age. Similar changes were observed in pituitary content and plasma levels of prolactin. Two immunoreactive bands of apparent molecular masses of 24 and 27 kDa, corresponding to the nonglycosylated and glycosylated form of prolactin, respectively, were visualized on Western blots. In pituitary glands from embryos at 22 days of incubation, 31.5% of the protein was glycosylated, whereas in embryos at 27 days of incubation and poults at 1 and 7 days of age, 48.6%, 48.0%, and 56. 0% of prolactin was glycosylated, respectively. The results indicate that the increases in the synthesis and the release of prolactin occur mainly around and after the time of hatching in the turkey embryo. Higher percentages of glycosylated isoforms were associated with increasing levels of total prolactin in the pituitary gland. Thus, the synthesis of prolactin and its post-translational modifications may be important factors involved in the physiologic changes occurring around the time of hatching.

Characterization of unique truncated prolactin receptor transcripts, corresponding to the intracellular domain, in the testis of the sexually mature chicken

We have examined expression of the chicken PRL receptor (cPRLR) gene in different tissues of the chicken by Northern blot analysis. Most tissues examined (ovary, testis, oviduct, kidney, and fat) possess a prominent full-length (4.6-kb) cPRLR transcript. A larger (11.7-kb) transcript is also detected in ovary, oviduct, testis, and kidney after longer exposure. A unique pattern of cPRLR expression was found in the testis of sexually mature chickens, which have an unusually high abundance of three small transcripts (1.2, 1.7, and 2 kb) in addition to the 4.6-kb transcript found in other tissues. Three domain-specific complementary DNA (cDNA) probes were constructed that correspond to the first and second ligand-binding regions in the extracellular domain and the transmembrane-intracellular domain. With these probes, Northern blot analysis of polyadenylated RNA prepared from the testes of a mature (22-week-old) chicken indicates that the highly abundant (1.2- and 1.7-kb) and less abundant (2.0-kb) cPRLR transcripts in testis hybridize only to the intracellular domain probe. Two types of truncated testis-specific cPRLR transcripts were identified using 5'-RACE (rapid amplification of cDNA ends) analysis of polyadenylated RNA from the testis of a 22-week-old chicken. The predominant truncated cDNA sequence contains the highly conserved box 1 motif [(+)box 1 cDNA] and diverges (at nucleotide 1396) from that of the cPRLR cDNA, just downstream of the transmembrane domain. The other truncated cDNA lacks the box 1 motif [(-)box 1 cDNA], which is replaced by 39 bases that could encode a hydrophobic N-terminus with a putative 5'-untranslated region of 131 bases. Young chickens predominately express the full-length cPRLR messenger RNA (4.6 kb) in the testis. At the onset of sexual maturity, there is a dramatic increase in abundance of the testis-specific (+)box 1 transcript, whereas expression of the full-length cPRLR is depressed. The presence of truncated [(+) or (-)box 1] cPRLR transcripts in the sexually mature chicken testis suggests a complex mechanism of PRL action on gonadal function.

In vitro release of isoforms of prolactin from pituitary glands of turkey hens at different physiological stages

To study the in vitro release of PRL isoforms, anterior pituitary glands from medium white turkeys at various physiological stages were stimulated by cVIP in a perifusion system. Pituitaries were cut into hemi-pituitaries after collection and placed into separate perifusion chambers. Medium (M199) was continuously perifused through the system and pituitaries were stimulated with cVIP (10(-7) M). Total PRL content was monitored by RIA and, the ratio of immunoreactive PRL isoforms in the perifusate was estimated by Western blotting. After exposure to X-ray film for autoradiography, the relative intensity of the bands was analyzed by densitometry. All the perifused pituitaries responded to cVIP stimulation by increasing the release of PRL. Two immunoreactive bands with relative molecular weights of 24 and 27 kDa were detected by Western blotting. The immunoreactive band corresponding to the glycosylated isoforms of PRL (27 kDa) was predominant in samples from egg-laying and incubating hens and the band corresponding to the nonglycosylated isoform (24 kDa) was predominant in samples from out-of-lay and molting stages. No changes in the ratio of isoform released were detected during cVIP stimulation. Our data clearly show that glycosylated and nonglycosylated PRL isoforms are released by the pituitary gland in vitro in the same relative proportion that was previously observed in pituitary extracts and thus are likely to reflect the secreted forms of PRL in the blood during various physiological stages. In addition, the PRL-releasing activity of VIP does not affect the ratio of isoforms secreted by the pituitary gland in vitro.

Changes in levels of immunoreactive prolactin isoforms during a reproductive cycle in turkey hens

Changes in the ratio between immunoreactive isoforms of prolactin using Western blotting and in the total prolactin content using radioimmunoassay were measured in pituitary glands from turkey hens at different physiological stages. The type of glycosylation (N- or O-linked carbohydrates) was determined using endoglycosidase digestion (N-glycosidase F, O-glycosidase, and neuraminidase). Low levels of prolactin were observed in pituitary glands from sexually immature, out-of-lay, and molting hens. Higher levels were present during the egg-laying period and the highest levels were detected in hens which expressed incubation behavior. Two immunoreactive bands of apparent molecular weights of 24 and 27 kDa were visualized on Western blots, corresponding to the nonglycosylated and glycosylated forms of prolactin, respectively. In pituitary glands from incubating turkey hens, about 70% of the prolactin was glycosylated (27-kDa isoforms), whereas about 60% was glycosylated in immature and in hens during the first egg-laying period. In pituitaries from out-of-lay and molting hens the percentage of glycosylated prolactin was 38 and 33%, respectively. Thus, higher percentages of glycosylated isoforms (27 kDa) were associated with high levels of total prolactin and lower percentages were associated with low levels of prolactin content in the pituitary gland. Digestion of the isoforms with N-glycosidase F resulted in a single band with an apparent molecular weight of 24 kDa. Partial deglycosylation was achieved using neuraminidase, whereas digestion with O-glycosidase had no apparent effect on the isoforms. Thus it appears that the glycosylated isoforms of prolactin have N-linked carbohydrates containing sialic acid.

Relationship between prolactin receptor mRNA in the anterior pituitary gland and hypothalamus and reproductive state in male and female bantams (Gallus domesticus)

The aim of this study was to test the hypothesis that prolactin may up- and down-regulate prolactin receptor gene expression in the anterior pituitary gland and hypothalamus respectively. Experiments were carried out in bantams (Gallus domesticus). Comparisons were made of concentrations of PRLR mRNA in the anterior pituitary gland and basal and preoptic hypothalamus in adult males and females held on long days (low vs high plasma prolactin); in 3-week-old juvenile male and females on short days (high vs low plasma prolactin); in 8-week-old juvenile male and females on short days (both low plasma prolactin); in adult laying, incubating, and out-of-lay (high, very high, and low plasma prolactin, respectively); in adult cockerels exposed to long or short days (high vs low prolactin); and in adult hens exposed to long or short days (high vs low prolactin). There was a sex difference in anterior pituitary and basal hypothalamic PRLR mRNA, with lower values in both tissues in females than in males. Compared with laying and out-of-lay hens, anterior pituitary and basal hypothalamic PRLR mRNA concentrations in incubating hens were increased and decreased, respectively. In adult birds of either sex held on long or short days, there was no difference in pituitary PRLR mRNA, while basal hypothalamic PRLR mRNA was lower on short days. PRLR mRNA in the preoptic hypothalamus was not affected by sex, reproductive state, or photoperiod. It is concluded that there is no consistent relationship between plasma prolactin, in the physiological range, and the concentration of PRLR mRNA in the anterior pituitary gland, basal hypothalamus, and preoptic hypothalamus.

Prolactin receptor gene expression in the brain and peripheral tissues in broody and nonbroody breeds of domestic hen

The objective of this study was to establish whether the gene encoding prolactin receptor (PRLR) is expressed in the hypothalamus and peripheral tissues of the domestic chicken and, if so, to determine whether there are breed differences in the structure or expression of the gene which might account for the observation that broodiness does not occur in the White Leghorn hen but does occur in other breeds of domestic hens, including the bantam. A preliminary experiment demonstrated that the absence of broodiness in White Leghorns is not due to a lack of a prolactin response to the avian prolactin-releasing hormone vasoactive intestinal polypeptide. The largest amounts of PRLR mRNA in the brain, which did not differ significantly between laying White Leghorns and bantams, were found in the pituitary gland and basal and preoptic hypothalamus. Small or nondetectable amounts were found in both breeds in the forebrain, cerebellum, and optic lobes. Prolactin receptor mRNA was widely distributed in peripheral tissues in both breeds, in the following descending order of abundance: kidney, leg skin, brood patch, duodenum, intestine > thyroid gland > adrenal gland, liver, ovary >> adipose tissue > thymus, spleen > muscle > blood. Southern blotting analysis using four restriction enzymes and a chicken PRLR cDNA probe demonstrated identical digestion patterns for White Leghorn and bantam genomic DNA. Northern blotting analysis identified two sizes of chicken PRLR mRNA transcripts (7.5 and 3.3 kb) in hypothalami from laying White Leghorn and bantam hens. It is concluded that differences in the expression of broodiness in White Leghorn and bantam hens cannot be explained by differences in the amounts of PRLR mRNA in the hypothalamus or in the transcription or gross structure of the PRLR gene.