Prolactin Receptor Gene Research Articles

Genetic Determinants of Nipple Aspiration Fluid Yield.

Nipple aspiration fluid (NAF) is a non-invasively-acquired biosample that can provide a window into the breast environment, but NAF yield is highly variable. Its determinants must be better understood for studies of breast cancer risk. The wet earwax phenotype was identified as one determinant of NAF yield in the 1970s, and is linked to single nucleotide polymorphisms (SNPs) in the ATP-binding cassette transporter gene ABCC11. We have investigated this, as well as SNPs in the prolactin (PRL) and prolactin receptor (PRLR) genes, in relation to NAF yield. DNA was extracted from white blood cells of 557 NAF yielders and 359 non-yielders, and was used to genotype ABCC11 (rs17822931), PRL (rs849870, rs849872, rs849886, rs2244502, rs1341239), and PRLR (rs37364, rs34024951, rs1610218, rs9292575, rs7718468) using Taqman genotyping assay. The association between NAF yield and each single SNP was analyzed using logistic regression adjusting for age, race, and menopausal status. ABCC11 rs17822931 showed a negative association with NAF yield [odds ratio (OR) 0.66, 95% confidence interval (CI) 0.49-0.88; p=0.004]. The PRL rs849870 and the haplotype combination with other SNPs showed a marginal association with NAF yield. In addition, the years since last birth also showed negative association with NAF yielding (OR 0.98, 95% CI 0.96-0.99; p=0.001). The combination of the years since last birth with ABCC11 SNP revealed significant interaction between reproductive factor and genetic factor. Our results confirmed the association between NAF yield and earwax phenotype through ABCC11 genotype. Combined with the recency of last birth, ABCC11 genotype should be considered in the design of studies utilizing NAF as a biosample.

Possible association between the prolactin receptor gene and callous-unemotional traits among aggressive children.

This study examined the possible association between prolactin (PRL) system genes and callous-unemotional (CU) traits in childhood-onset aggression. Two markers for the PRL peptide gene and three markers for the prolactin receptor (PRLR) gene were genotyped. The participants were assessed on the CU subscale using five items from the Antisocial Process Screening Device. Genotype analysis showed nominally significant results with PRLR_rs187490 (uncorrected P=0.01), with the GG genotype associated with higher CU scores. This is the first paper to evaluate the relationship of PRL system genes with CU traits in childhood-onset aggression.

PRLR-AluI Gene Polymorphism And Litter Size Traits In Highly Prolific Line Of Topigs 20 Sows

Abstract The objective of the present study was to identify the Prolactin Receptor (PRLR) gene polymorphism related to litter size traits. The study included 101 Topigs 20 line of sows with 426 litters. The traits studied were: Total Number of Born (TNB), Number of Born Alive (NBA), Number of Still Born (NSB), and Number of MUMmified (NMUM) piglets. Polymorphism was identified with the polymerase chain reaction-restriction fragment length polymorphism method. Allelic and genotype frequencies and deviation from Hardy-Weinberg equilibrium were verified with the chi-square test. Analysis of litter size traits was performed using the General Linear Model, which included the potential environmental effects. Additive and dominant allele variances were observed by the regression procedure. In the studied population of sows, the frequency of heterozygotes (0.5149) for PRLR gene exceeded the total number of AA (0.0198) and BB (0.4653) homozygotes, which resulted in a high proportion of B allele (0.7228). The results for PRLR showed statistically significant (P<0.05) differences in first parity sows between BB and AB genotypes for TNB and NBA. Significant differences (P<0.05) were recorded in third parity sows between BB and AB genotypes for NBA, and in AA genotype versus AB and BB genotypes for NMUM. The fourth and subsequent parity sows of AA genotype had a significantly higher (P<0.05) rate of NBA as compared with those of AB and BB genotypes. In all parities analysed, the difference between the BB and AB genotypes for NBA was statistically significant (P<0.05). Interpretation of the results at the levels of phenotypes and either additive or dominant variance was quite difficult due to the small number of AA homozygous sows. The calculation model yielded a significant effect (P<0.05) as well as tendency (P<0.1) for the mentioned effects except for age at first farrowing.

Cloning, expression of, and evidence of positive selection for, the prolactin receptor gene in Chinese giant salamander (Andrias davidianus).

Prolactin receptor (PRLR) is a protein associated with reproduction in mammals and with osmoregulation in fish. In this study, the complete length of Chinese giant salamander Andrias davidianus prolactin receptor (AD-prlr) was cloned. Andrias davidianus prlr expression was high in the kidney, pituitary, and ovary and low in other examined tissues. The AD-prlr levels were higher in ovary than in testis, and increased in ovaries with age from 1 to 6 years. To determine effect of exogenous androgen and aromatase inhibitor on AD-prlr expression, methyltestosterone (MT) and letrozole (LE) were injected, resulting in decreased AD-prlr in both brain and ovary, with MT repressing prlr transcription more rapidly than did LE. The molecular evolution of prlr was assessed, and found to have undergone a complex evolution process. The obranch-site test detected four positively selected sites in ancestral lineages prior to the separation of mammals and birds. Fourteen sites underwent positive selection in ancestral lineages of birds and six were positively selected in amphibians. The site model showed that 16, 7, and 30 sites underwent positive selection in extant mammals, amphibians, and birds, respectively. The positively selected sites in amphibians were located outside the transmembrane domain, with four in the extracellular and three in the intracellular domain, indicating that the transmembrane region might be conserved and essential for protein function. Our findings provide a basis for further studies of AD-prlr function and molecular evolution in Chinese giant salamander. J. Exp. Zool. (Mol. Dev. Evol.) 324B: 707-719, 2015. © 2015 Wiley Periodicals, Inc.

Endocrine control of canine mammary neoplasms: serum reproductive hormone levels and tissue expression of steroid hormone, prolactin and growth hormone receptors.

BackgroundNeoplasms of the mammary gland are among the most common diseases in female domestic dogs (Canis familiaris). It is assumed that reproductive hormones influence tumorigenesis in this species, although the precise role of the endocrine milieu and reproductive state is subject to continuing discussion. In line with this, a recent systematic review of available data on the development of mammary neoplasms revealed weak evidence for risk reduction after neutering and an effect of age at neutering. Investigation of several hormone receptors has revealed decreased expression of estrogen receptor-alpha (ERα, ESR1), progesterone (P4) receptor (PGR), prolactin (PRL) receptor (PRLR) and growth hormone receptor (GHR) associated with neoplastic differentiation of mammary tissues. In other studies, increased levels of estrogens, progesterone and prolactin were found in serum and/or tissue homogenates of dogs with malignant neoplasms. However, the association between these entities within one animal population was never previously examined. Therefore, this study investigated the association between circulating serum concentrations of estradiol-17β, progesterone and prolactin, and gene expression of ERα (ESR1), ERβ (ESR2), PGR, PRLR, PRL and GHR, with respect to reproductive state (spayed vs. intact) and cycle stage (anestrus vs. diestrus). Additionally, the expression of E-cadherin (CDH-1) was evaluated as a possible indicator of metastatic potential.ResultsFor all receptors, the lowest gene expression was found in malignant tumors compared to normal tissues of affected dogs. Steroid levels were not influenced by their corresponding receptor expression in mammary neoplasms, but increased PRL levels were negatively associated with low PRLR gene expression in malignant tumors. The expression of CDH-1 was influenced by tumor malignancy and cycle stage, i.e., the highest gene expression was found in benign mammary tumors in diestrous dogs compared to normal and malignant mammary tissues of anestrous and spayed dogs.ConclusionsHerein, it has been confirmed that transformation towards malignant neoplasms is associated with significant reduction of gene expression of particular hormone receptors. Only PRLR in malignant tumors seems to be influenced by circulating PRL levels. In dogs, CDH-1 can be used as a prognostic factor; its expression, however, in benign tumors is influenced by cycle stage.Electronic supplementary materialThe online version of this article (doi:10.1186/s12917-015-0546-y) contains supplementary material, which is available to authorized users.

Coexisting Prolactinoma and Primary Aldosteronism: Is There a Pathophysiological Link?

Coexisting prolactinoma-primary aldosteronism (PA) is infrequently reported. The objective of the study was to identify patients with prolactinoma-PA and test the hypothesis that elevated prolactin (PRL) concentrations play a role in PA pathogenesis. Hyperprolactinemia/prolactinoma was diagnosed in PA patients from two referral centers (Munich, Germany, and Turin, Italy) and in essential hypertensive (EH) patients from one center (Turin). PRL receptor (PRLR) gene expression was determined by microarrays on aldosterone-producing adenomas and normal adrenals and validated by real-time PCR. H295R adrenal cells were incubated with 100 nM PRL, and gene expression levels were determined by real-time PCR and aldosterone production was quantified. Seven patients with prolactinoma-PA were identified: four of 584 and three of 442 patients from the Munich and Turin PA cohorts, respectively. A disproportionate number presented with macroprolactinomas (five of seven). There were five cases of hyperprolactinemia with no cases of macroprolactinoma of 14 790 patients in a general EH cohort. In a population of PA patients case-control matched 1:3 with EH patients there were two cases of hyperprolactinemia of 270 PA patients and no cases in the EH cohort (n = 810). PRLR gene expression was significantly up-regulated in the aldosterone-producing adenomas compared with normal adrenals (1.7-fold and 1.5-fold by microarray and real-time PCR, respectively). In H295R cells, PRL treatment resulted in 1.3-fold increases in CYP11B2 expression and aldosterone production. Elevated PRL caused by systemic hyperprolactinemia may contribute to the development of PA in those cases in which the two entities coexist.

Evaporative cooling in late-gestation Murrah buffaloes potentiates immunity around transition period and overcomes reproductive disorders

The objective of the study was to observe the effect of evaporative cooling during late gestation on immunity around the transition period and the probable outcome on reproductive disorders in Murrah buffaloes. Sixteen pregnant dry Murrah buffaloes at 60 days prepartum were selected and divided into two groups of eight animals each. Group 1 buffaloes remained without the provision of cooling, whereas the second group of buffaloes was managed under fans and mist cooling during the dry period. After parturition, all the animals were managed under evaporative cooling. Dry matter intake was significantly (P < 0.05) higher in cooled relative to noncooled animals at −15, 0, and +20 days of parturition. Cortisol and prolactin levels were significantly (P < 0.05) higher in noncooled relative to cooled animals at −15 and 0 days of parturition. However, prolactin was significantly (P < 0.05) higher in cooled animals at +20 days. Messenger RNA expression of prolactin receptor gene (PRL-R) was upregulated and suppressor of cytokine signaling gene 1 (SOCS-1) was downregulated in cooled animals at −20, 0, and +20 days of parturition. Tumor necrosis factor α and interleukin 4 levels remained significantly (P < 0.05) higher in cooled animals at −20, 0, and +20 days of parturition. Interleukin 6 was significantly (P < 0.05) lower in cooled animals at −20 and 0 days. Interferon γ levels were significantly higher at −20 and +20 days of parturition in cooled relative to noncooled animals. The reproductive disorders such as retention of placenta, metritis, and endometritis occurred at the rate of 37.25%, 25%, and 12.25% in the noncooled group, whereas only retention of placenta was observed in the cooled (12.5%) group.

MiR-135a Targets and Regulates Prolactin Receptor Gene in Goat Mammary Epithelial Cells.

Mammary gland development and lactation are typical traits controlled by multiple genes, hormones, and regulatory factors. Prolactin receptor (PRLR), a specific receptor of prolactin, has been reported to have important physiological functions in regulating mammogenesis and lactogenesis. However, the post-transcriptional regulation mechanisms of PRLR expression have not yet been shown in detail. In this study, the expression of miR-135a and PRLR at different development stages of Laoshan dairy goat mammary gland tissues was investigated. After overexpression and silencing expression of miR-135a in cultured primary mammary epithelial cells, the regulatory relationship between miR-135a and PRLR was examined through dual-luciferase reporter assay, and the expression of PRLR at both mRNA and protein levels was examined by real-time quantitative polymerase chain reaction (RT-qPCR) and western blot. Collectively, our results suggested that PRLR is a direct target gene of miR-135a, miR-135a is a novel regulator of PRLR, and it might play an essential role in the regulation of animal mammary gland development and lactation.

Effect of Prolactin Receptor (PRLR) and Beta-Casein (CSN2) Gene Polymorphism on the Chemical Composition of Milk Sows.

The objective of the studies was to evaluate the impact of the prolactin receptor and β-casein genes on the basic chemical composition and pH of the colostrum and milk of sows. Experiments were carried out on 103 Złotnicka White breed sows. These animals are under the Domestic Program of Protection of Genetic Resources. Analysis of the influence of polymorphism in the PRLR and CSN2 loci revealed that sows of the TT homozygote were characterised by the highest dry matter content. Analysis of polymorphism in the PRLR locus for protein showed that the highest values were in milk of sows of the TT genotype, and GG homozygotes in the case of the CSN2 locus. Inference of the impact of polymorphism in the PRLR and CSN2 loci on the fat and lactose content of sow milk demonstrated considerable variability. These differences were statistically significant at the level of α = 0.01 and α = 0.05. Periodical changes in individual pH values were apparent for particular genotypes in both loci (PRLR and CSN2). The perceptible changes that occurred between individual genotypes were statistically significant at the levels of α = 0.01 and α = 0.05. The investigations confirmed that the nutritive values of sow colostrum and milk were determined by genetic factors. This issue warrants comprehensive analysis, especially in terms of evaluation of the breeding value of maternal breeds.

Brief overview of the polymorphism analysis of genes affecting pig prolificacy (LEP, PRLP, ESR BF, EGF, FSH-β, H2A.Z)

Researches are being performed around the world to increase swine prolificacy by using marker-assisted selection (MAS). The present study processes researches of polymorphism examinations on 7 genes. The result of the experiments showed that the leptin gene (LEP) prolactin receptor gene (PRLP), estrogen receptor gene (ESR), properdin B (BF) epidermal growth factor (EGF), follicle-stimulating beta gene (FSH-ß) and Z member of the H2A histon family gene (H2A.Z) and their alleles have a positive effect on reproductive characteristics of different swine breeds. In addition to this, leptin gene (LEP) influences the build, meat production and growth of body fat. Further studies are concerned with the polymorphism of an increasing number of genes, which enables a faster genetic development of swine breeding.

Single-nucleotide polymorphisms g.151435C>T and g.173057T>C in PRLR gene regulated by bta-miR-302a are associated with litter size in goats

Single-nucleotide polymorphisms (SNPs) located at microRNA-binding sites (miR-SNPs) can affect the expression of genes. This study aimed to identify the miR-SNPs associated with litter size. Guanzhong (n = 321) and Boer (n = 191) goat breeds were used to detect SNPs in the caprine prolactin receptor (PRLR) gene by DNA sequencing, primer-introduced restriction analysis-polymerase chain reaction, and polymerase chain reaction-restriction fragment length polymorphism. Three novel SNPs (g.151435C>T, g.151454A>G, and g.173057T>C) were identified in the caprine PRLR gene. Statistical results indicated that the g.151435C>T and g.173057T>C SNPs were significantly associated with litter size in Guanzhong and Boer goat breeds. Further analysis revealed that combinative genotype C6 (TTAACC) was better than the others for litter size in both goat breeds. Furthermore, the PRLR g.173057T>C polymorphism was predicted to regulate the binding activity of bta-miR-302a. Luciferase reporter gene assay confirmed that 173057C to T substitution disrupted the binding site for bta-miR-302a, resulting in the reduced levels of luciferase. Taken together, these findings suggested that bta-miR-302a can influence the expression of PRLR protein by binding with 3′untranslated region, resulting in that the g.173057T>C SNP had significant effects on litter size.

Identification of SNPs within the PRLR gene and effects on maternal behavior in sheep.

The prolactin receptor gene (PRLR) plays an essential role in maternal behavior. The aim of the study was to detect PRLR mutations in exon 10, using a polymerase chain reaction-single stranded conformation polymorphism method, and to determine the association between mutations in this region with maternal behavior traits in Chinese Hu sheep. Polymorphisms were detected only in the gene region amplified by the primer P3; three genotypes (AA, AB and BB) were observed. The genotype BB was predominant in the ewe study population, and genotype distributions were in agreement with the Hardy-Weinberg equilibrium (P > 0.05). There was no significant difference between observations for licking and kicking behaviors of AA and AB genotype individuals (P > 0.05), but there was a significant difference (0.01 < P ≤ 0.05), when both were compared with the BB genotype. Significant differences were observed in suckling behavior between AA and AB genotype individuals (0.01 < P ≤ 0.05), and the difference between these two genotypes and BB was highly significant (P ≤ 0.01). No obvious difference was observed between the genotypes in behavior of suckling rejection (P > 0.05). These results contribute to methods for selection and breeding through marker-assisted selection for maternal behavior traits in Hu sheep.

MRNA expression of prolactin receptor in sheep pituitary and its effect on maternal behavior.

Prolactin receptor (PRLR) is the specific receptor for prolactin. Brain-specific control of PRLR gene expression is correlated with the induction of maternal behavior. The aim of this study was to investigate the dynamic changes in the PRLR mRNA level in the sheep pituitary gland and its effect on ewe maternal behavior. The mRNA expression of PRLR during non-pregnancy stage was maintained at low but detectable levels, as was the case during mid-gestation. After that, expression began increasing and reached a maximum during the early postpartum followed by a gradual decline during the mid-postpartum and late postpartum stages. A trend of higher PRLR mRNA expression was observed during the postpartum stage relative to the non-pregnancy and pregnancy stages. Expression of PRLR mRNA was significantly higher in the normal maternal behavior group than that in the abnormal maternal behavior group. There may be a correlation between PRLR mRNA expression and ewe maternal behavior, especially in early postpartum.

Two missense mutations in exon 9 of caprine PRLR gene were associated with litter size.

Guanzhong (n=321) and Boer (n=191) goat breeds were used to detect single nucleotide polymorphisms (SNPs) in the coding regions of the prolactin receptor (PRLR) gene by DNA sequencing and PCR-RFLP. Two SNPs (c.1457G>A and c.1645G>A) were identified that caused amino acid variations p.Ser485Asn and p.Val548Met respectively. Statistical results indicated that the c.1457G>A and c.1645G>A SNPs were significantly associated with litter size in Boer and Guanzhong goat breeds. Further analysis revealed that combined genotype C4 (GGGG) and haplotype G-G were better than the others for litter size in both goat breeds. These results might contribute to goat genetic resources and breeding.

PreImplantation factor (PIF*) promotes embryotrophic and neuroprotective decidual genes: effect negated by epidermal growth factor.

BackgroundIntimate embryo-maternal interaction is paramount for pregnancy success post-implantation. The embryo follows a specific developmental timeline starting with neural system, dependent on endogenous and decidual factors. Beyond altered genetics/epigenetics, post-natal diseases may initiate at prenatal/neonatal, post-natal period, or through a continuum. Preimplantation factor (PIF) secreted by viable embryos promotes implantation and trophoblast invasion. Synthetic PIF reverses neuroinflammation in non-pregnant models. PIF targets embryo proteins that protect against oxidative stress and protein misfolding. We report of PIF’s embryotrophic role and potential to prevent developmental disorders by regulating uterine milieu at implantation and first trimester.MethodsPIF’s effect on human implantation (human endometrial stromal cells (HESC)) and first-trimester decidua cultures (FTDC) was examined, by global gene expression (Affymetrix), disease-biomarkers ranking (GeneGo), neuro-specific genes (Ingenuity) and proteins (mass-spectrometry). PIF co-cultured epidermal growth factor (EGF) in both HESC and FTDC (Affymetrix) was evaluated.ResultsIn HESC, PIF promotes neural differentiation and transmission genes (TLX2, EPHA10) while inhibiting retinoic acid receptor gene, which arrests growth. PIF promotes axon guidance and downregulates EGF-dependent neuroregulin signaling. In FTDC, PIF promotes bone morphogenetic protein pathway (SMAD1, 53-fold) and axonal guidance genes (EPH5) while inhibiting PPP2R2C, negative cell-growth regulator, involved in Alzheimer’s and amyotrophic lateral sclerosis. In HESC, PIF affects angiotensin via beta-arrestin, transforming growth factor-beta (TGF-β), notch, BMP, and wingless-int (WNT) signaling pathways that promote neurogenesis involved in childhood neurodevelopmental diseases—autism and also affected epithelial-mesenchymal transition involved in neuromuscular disorders. In FTDC, PIF upregulates neural development and hormone signaling, while downregulating genes protecting against xenobiotic response leading to connective tissue disorders.In both HESC and FTDC, PIF affects neural development and transmission pathways. In HESC interactome, PIF promotes FUS gene, which controls genome integrity, while in FTDC, PIF upregulates STAT3 critical transcription signal. EGF abolished PIF’s effect on HESC, decreasing metalloproteinase and prolactin receptor genes, thereby interfering with decidualization, while in FTDC, EGF co-cultured with PIF reduced ZHX2, gene that regulates neural AFP secretion.ConclusionsPIF promotes decidual trophic genes and proteins to regulate neural development. By regulating the uterine milieu, PIF may decrease embryo vulnerability to post-natal neurodevelopmental disorders. Examination of PIF-based intervention strategies used during embryogenesis to improve pregnancy prognosis and reduce post-natal vulnerability is clearly in order.

Associations between PRLR/AluI gene polymorphism with reproductive, growth, and meat traits in pigs

The aim of this study was to determine the associations between genotypes of the prolactin receptor gene (PRLR) and reproductive, growth, and meat traits in pigs. Genetic groups of sows were used: Large White (LW), Danish Landrace (LD), and Landrace × Yorkshire × Duroc hybrids (L × Y × D). Reproductive traits studied were the total number of born (TNB) and the number born alive (NBA). The growth traits were the number of days to 100 kg and the average daily gains (ADG). The meat traits were the average backfat thickness (BFT), half carcass weight (HCW), area of M. longissimus dorsi (MLT), and lean meat content (LM). The polymorphism was detected using the polymerase chain reaction-restriction fragment-length polymorphism (PCR-RFLP) method. It was found that the genotype BB is associated with the best NBA. In sows LD, the AB genotype is associated with best number of days to 100 kg; in hybrids L × Y × D, the AA genotype is associated with better meat traits as compared to the genotype BB.

Prolactin increases tumor necrosis factor alpha expression in peripheral CD14 monocytes of patients with rheumatoid arthritis

Tumor necrosis factor (TNF)-α is one of the major proinflammatory mediators of rheumatic arthritis (RA); the regulatory factors for TNF-α release is not fully understood. This study aims to investigate the role of prolactin receptor (PRLR) activation in regulating the expression and release of TNF-α from CD14+ monocytes. The results showed that the expression of PRLR was detectable in CD14+ monocytes of healthy subjects, which was markedly increased in RA patients. Exposure to PRL in the culture increased the expression and release of TNF-α from CD14+ monocytes, which was abolished by the PRLR gene silencing or blocking the mitogen activated protein (MAPK) pathway. We conclude that exposure to PRL increases TNF-α release from CD14+ monocytes of RA patients, which can be abolished by PRLR gene silencing or treating with MAPK inhibitor.

Different expression of prolactin receptor gene in rat duodenum during physiological and medicamentous hyperprolactinemia

Different expression of prolactin receptor gene in rat duodenum during physiological and medicamentous hyperprolactinemia

A recent L1 insertion withinSPEF2gene is associated with changes inPRLRexpression in sow reproductive organs

The immotile short tail sperm (ISTS) defect was recognized in the Finnish Yorkshire population at the end of the 1990s when several affected boars were identified. The causal mutation for this defect is a recent L1 insertion within the SPEF2 gene. In 2001, the insertion frequency was already 0.23. Even though all homozygous boars are eliminated from the population due to infertility, the amount of affected boars increased rapidly until marker-assisted selection against the defect was established. Previously we identified an association between the L1 insertion and litter size in the first parity. In this study, we analyzed the expression of the genomic region adjacent to the L1 insertion on porcine chromosome 16. Based on the RNA-seq data analysis, prolactin receptor (PRLR) was identified as down-regulated in the oviduct of ISTS homozygous sows. Quantitative PCR (qPCR) analysis confirmed the significant down-regulation of PRLR in the ovary, oviduct, and uterus of ISTS homozygous and carrier sows compared with controls. In addition, three unannotated loci between PRLR and SPEF2 showed some transcription activity in the analyzed samples. We further investigated the possible mechanisms of the L1 influence on the decrease in the identified gene expression. The methylation pattern of the PRLR gene region appeared unaffected. However, reads mapping to the L1 sequence indicated an increase in L1 antisense promoter expression in the ISTS homozygous animals. The current data suggest that the presence of the L1 affects by some mechanism the expression patterns upstream of the insertion site.

Prolactin (PRL) and prolactin receptor (PRLR) genes and their role in poultry production traits.

Prolactin (PRL), secreted from the anterior pituitary, plays extensive roles in osmoregulation, corpus luteum formation, mammogenesis, lactogenesis, lactopoiesis, and production of crop milk. In birds, prolactin (PRL) is generally accepted as crucial to the onset and maintenance of broodiness. All the actions of prolactin (PRL) hormone are mediated by its receptor (PRLR), which plays an important role in the PRL signal transduction cascade. It has been well established that the PRL gene is closely associated to the onset and maintenance of broody behavior, and could be a genetic marker in breeding against broodiness in chickens. Meanwhile, the prolactin receptor (PRLR) gene is regarded as a candidate genetic marker for reproductive traits. PRLR is also an important regulator gene for cell growth and differentiation. The identified polymorphism of this gene is mainly viewed in terms of egg production traits. Due to different biological activities attributed to PRL and PRLR, they can be used as major candidate genes in molecular animal breeding programs. Characterization of PRL and PRLR genes helps to elucidate their roles in birds and provides insights into the regulatory mechanisms of PRL and PRLR expression conserved in birds and mammals.