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

The AKT1-FOXO4 axis reciprocally regulates hemochorial placentation

Hemochorial placentation involves the differentiation of invasive trophoblast cells, specialized cells that possess the capacity to exit the placenta and invade into the uterus where they restructure the vasculature. Invasive trophoblast cells arise from a well-defined compartment within the placenta, referred to as the junctional zone in rat and the extravillous trophoblast cell column in human. In this study, we investigated roles for AKT1, a serine/threonine kinase, in placental development using a genome-edited/loss-of-function rat model. Disruption of AKT1 resulted in placental, fetal and postnatal growth restriction. Forkhead box O4 (Foxo4), which encodes a transcription factor and known AKT substrate, was abundantly expressed in the junctional zone and in invasive trophoblast cells of the rat placentation site. Foxo4 gene disruption using genome editing resulted in placentomegaly, including an enlarged junctional zone. AKT1 and FOXO4 regulate the expression of many of the same transcripts expressed by trophoblast cells, but in opposite directions. In summary, we have identified AKT1 and FOXO4 as part of a regulatory network that reciprocally controls critical indices of hemochorial placenta development.

Do some viruses use growth hormone, prolactin and their receptors to facilitate entry into cells?: Episodic evolution of hormones and receptors suggests host-virus arms races; related placental lactogens may provide protective viral decoys

The molecular evolution of pituitary growth hormone and prolactin in mammals shows two unusual features: episodes of markedly accelerated evolution and, in some species, complex families of related proteins expressed in placenta and resulting from multiple gene duplications. Explanations of these phenomena in terms of physiological adaptations seem unconvincing. Here, I propose an alternative explanation, namely that these evolutionary features reflect the use of the hormones (and their receptors) as viral receptors. Episodes of rapid evolution can then be explained as due to "arms races" in which changes in the hormone lead to reduced interaction with the virus, and subsequent changes in the virus counteract this. Placental paralogues of the hormones could provide decoys that bind viruses, and protect the foetus against infection. The hypothesis implies that the extensive changes introduced into growth hormone, prolactin and their receptors during the course of mammalian evolution reflect viral interactions, not endocrine adaptations.

Short prolactin isoforms are expressed in photoreceptors of canine retinas undergoing retinal degeneration

Prolactin (PRL) hormone functions as a pleiotropic cytokine with a protective role in the retina. We recently identified by transcriptome profiling that PRL is one of the most highly upregulated mRNAs in the retinas of mutant rcd1 (PDE6B) and xlpra2 (RPGR) dogs at advanced stages of photoreceptor disease. In the present study, we have identified the expression of a short PRL isoform that lacks exon 1 in canine retinas and analyzed the time-course of expression and localization of this isoform in the retinas of these two models. Using laser capture microdissection to isolate RNA from each of the retinal cellular layers, we found by qPCR that this short PRL isoform is expressed in photoreceptors of degenerating retinas. We confirmed by in situ hybridization that its expression is localized to the outer nuclear layer and begins shortly after the onset of disease at the time of peak photoreceptor cell death in both models. PRL protein was also detected only in mutant dog retinas. Our results call for further investigations into the role of this novel PRL isoform in retinal degeneration.

Variation in the Evolution and Sequences of Proglucagon and the Receptors for Proglucagon-Derived Peptides in Mammals

The mammalian proglucagon gene (Gcg) encodes three glucagon like sequences, glucagon, glucagon-like peptide-1 (GLP-1), and glucagon-like peptide-2 that are of similar length and share sequence similarity, with these hormones having cell surface receptors, glucagon receptor (Gcgr), GLP-1 receptor (Glp1r), and GLP-2 receptor (Glp2r), respectively. Gcgr, Glp1r, and Glp2r are all class B1 G protein-coupled receptors (GPCRs). Despite their sequence and structural similarity, analyses of sequences from rodents have found differences in patterns of sequence conservation and evolution. To determine whether these were rodent-specific traits or general features of these genes in mammals I analyzed coding and protein sequences for proglucagon and the receptors for proglucagon-derived peptides from the genomes of 168 mammalian species. Single copy genes for each gene were found in almost all genomes. In addition to glucagon sequences within Hystricognath rodents (e.g., guinea pig), glucagon sequences from a few other groups (e.g., pangolins and some bats) as well as changes in the proteolytic processing of GLP-1 in some bats are suggested to have functional effects. GLP-2 sequences display increased variability but accepted few substitutions that are predicted to have functional consequences. In parallel, Glp2r sequences display the most rapid protein sequence evolution, and show greater variability in amino acids at sites involved in ligand interaction, however most were not predicted to have a functional consequence. These observations suggest that a greater diversity in biological functions for proglucagon-derived peptides might exist in mammals.

Hemochorial placentation: development, function, and adaptations

Placentation is a reproductive adaptation that permits fetal growth and development within the protected confines of the female reproductive tract. Through this important role, the placenta also determines postnatal health and susceptibility to disease. The hemochorial placenta is a prominent feature in primate and rodent development. This manuscript provides an overview of the basics of hemochorial placental development and function, provides perspectives on major discoveries that have shaped placental research, and thoughts on strategies for future investigation.

Evolution of the growth hormone, prolactin, prolactin 2 and somatolactin family

Growth hormone (GH), prolactin (PRL), prolactin 2 (PRL2) and somatolactin (SL) belong to the same hormone family and have a wide repertoire of effects including development, osmoregulation, metabolism and stimulation of growth. Both the hormone and the receptor family have been proposed to have expanded by gene duplications in early vertebrate evolution. A key question is how hormone-receptor preferences have arisen among the duplicates. The first step to address this is to determine the time window for these duplications. Specifically, we aimed to see if duplications resulted from the two basal vertebrate tetraploidizations (1R and 2R). GH family genes from a broad range of vertebrate genomes were investigated using a combination of sequence-based phylogenetic analyses and comparisons of synteny. We conclude that the PRL and PRL2 genes arose from a common ancestor in 1R/2R, as shown by neighboring gene families. No other gene duplicates were preserved from these tetraploidization events. The ancestral genes that would give rise to GH and PRL/PRL2 arose from an earlier duplication; most likely a local gene duplication as they are syntenic in several species. Likewise, some evidence suggests that SL arose from a local duplication of an ancestral GH/SL gene in the same time window, explaining the lack of similarity in chromosomal neighbors to GH, PRL or PRL2. Thus, the basic triplet of ancestral GH, PRL/PRL2 and SL genes appear to be unexpectedly ancient. Following 1R/2R, only SL was duplicated in the teleost-specific tetraploidization 3R, resulting in SLa and SLb. These time windows contrast with our recent report that the corresponding receptor genes GHR and PRLR arose through a local duplication in jawed vertebrates and that both receptor genes duplicated further in 3R, which reveals a surprising asynchrony in hormone and receptor gene duplications.

Hypoxia and Placental Development

Hemochorial placentation is orchestrated through highly regulated temporal and spatial decisions governing the fate of trophoblast stem/progenitor cells. Trophoblast cell acquisition of specializations facilitating invasion and uterine spiral artery remodeling is a labile process, sensitive to the environment, and represents a process that is vulnerable to dysmorphogenesis in pathologic states. Hypoxia is a signal guiding placental development, and molecular mechanisms directing cellular adaptations to low oxygen tension are integral to trophoblast cell differentiation and placentation. Hypoxia can also be used as an experimental tool to investigate regulatory processes controlling hemochorial placentation. These developmental processes are conserved in mouse, rat, and human placentation. Consequently, elements of these developmental events can be modeled and hypotheses tested in trophoblast stem cells and in genetically manipulated rodents. Hypoxia is also a consequence of a failed placenta, yielding pathologies that can adversely affect maternal adjustments to pregnancy, fetal health, and susceptibility to adult disease. The capacity of the placenta for adaptation to environmental challenges highlights the importance of its plasticity in safeguarding a healthy pregnancy. Birth Defects Research 109:1309-1329, 2017.© 2017 Wiley Periodicals, Inc.

A Prolactin Family Paralog Regulates Placental Adaptations to a Physiological Stressor

The prolactin (PRL) family of hormones and cytokines participates in the regulation of optimal reproductive performance in the mouse and rat. Members of the PRL family are expressed in the anterior pituitary, uterus, and/or placenta. In the present study, we investigated the ontogeny of PRL family 7, subfamily b, member 1 (PRL7B1; also called PRL-like protein-N, PLP-N) expression in the developing mouse placenta and established a mouse model for investigating the biological function of PRL7B1. Transcripts for Prl7b1 were first detected on Gestation Day (d) 8.5. From gestation d8.5 through d14.5, Prl7b1 was expressed in trophoblast cells residing at the interface between maternal mesometrial decidua and the developing placenta. On gestation d17.5, the predominant cellular source of Prl7b1 mRNA was migratory trophoblast cells invading into the uterine mesometrial decidua. The Prl7b1 null mutant allele was generated via replacement of the endogenous Prl7b1 coding sequence with beta-galactosidase (LacZ) reporter and neomycin cassettes. The mutant Prl7b1 allele was successfully passed through the germline. Homozygous Prl7b1 mutant mice were viable and fertile. Under standard animal housing conditions, Prl7b1 had undetectable effects on placentation and pregnancy. Hypoxia exposure during pregnancy evoked adaptations in the organization of the wild-type placenta that were not observed in Prl7b1 null placentation sites. In summary, PRL7B1 is viewed as a part of a pathway regulating placental adaptations to physiological stressors.

Identification of target genes for a prolactin family paralog in mouse decidua

Prolactin family 8, subfamily a, member 2 (PRL8A2; also called decidual prolactin-related protein; dPRP) is a member of the expanded prolactin family. PRL8A2 is expressed in the uterine decidua and contributes to pregnancy-dependent adaptations to hypoxia. The purpose of this study was to identify gene targets for PRL8A2 action within the uteroplacental compartment. Affymetrix DNA microarray analysis was performed for RNA samples from WT and Prl8a2 null tissues. Validation of the DNA microarray was performed using quantitative RT-PCR. Nine genes were confirmed with decreased expression in Prl8a2 null tissues (e.g., Klk7, Rimklb, Arhgef6, Calm4, Sprr2h, Prl4a1, Ccl27, Lipg, and Htra3). These include potential decidual, endothelial and trophoblast cell targets positively regulated by PRL8A2. A significant upregulation of Derl3, Herpud1, Creld2, Hsp90b1, Ddit3 and Hspa5 was identified in Prl8a2 null tissues, reflecting an increased endoplasmic reticulum (ER) stress response. ER stress genes were prominently expressed in the uterine decidua. We propose that PRL8A2 is a mediator of progesterone-dependent modulation of intrauterine responses to physiological stressors.

Overexpression of PRL7D1 in Leydig Cells Causes Male Reproductive Dysfunction in Mice

Prolactin family 7, subfamily d, member 1 (PRL7D1) is found in mouse placenta. Our recent work showed that PRL7D1 is also present in mouse testis Leydig cells, and the expression of PRL7D1 in the testis exhibits an age-related increase. In the present study, we generated transgenic mice with Leydig cell-specific PRL7D1 overexpression to explore its function during male reproduction. Prl7d1 male mice exhibited subfertility as reflected by reduced sperm counts and litter sizes. The testes from Prl7d1 transgenic mice appeared histologically normal, but the frequency of apoptotic germ cells was increased. Prl7d1 transgenic mice also had lower testosterone concentrations than wild-type mice. Mechanistic studies revealed that Prl7d1 transgenic mice have defects in the testicular expression of steroidogenic acute regulatory protein (STAR) and hydroxy-delta-5-steroid dehydrogenase, 3 beta- and steroid delta-isomerase cluster (HSD3B). Further studies revealed that PRL7D1 overexpression affected the expression of transferrin (TF) in Sertoli cells. These results suggest that PRL7D1 overexpression could lead to increased germ cell apoptosis and exert an inhibitory effect on testosterone production in Leydig cells by reducing the expression of certain steroidogenic-related genes. In addition, PRL7D1 appears to have important roles in the function of Sertoli cells, which, in turn, affects male fertility. We conclude that the expression level of PRL7D1 is associated with the reproductive function of male mice.

Principles of the prolactin/vasoinhibin axis

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

Consequence of Menin Deficiency in Mouse Adipocytes Derived by In Vitro Differentiation

Lipoma in patients with the multiple endocrine neoplasia type 1 (MEN1) syndrome is a type of benign fat-cell tumor that has biallelic inactivation of MEN1 that encodes menin and could serve as a model to investigate normal and pathologic fat-cell (adipocyte) proliferation and function. The role of menin and its target genes in adipocytes is not known. We used in vitro differentiation to derive matched normal and menin-deficient adipocytes from wild type (WT) and menin-null (Men1-KO) mouse embryonic stem cells (mESCs), respectively, or 3T3-L1 cells without or with menin knockdown to investigate cell size, lipid content, and gene expression changes. Adipocytes derived from Men1-KO mESCs or after menin knockdown in 3T3-L1 cells showed a 1.5-1.7-fold increase in fat-cell size. Global gene expression analysis of mESC-derived adipocytes showed that lack of menin downregulated the expression of many differentially methylated genes including the tumor suppressor long noncoding RNA Meg3 but upregulated gene expression from the prolactin gene family locus. Our results show that menin deficiency leads to fat-cell hypertrophy and provide model systems that could be used to study the regulation of fat-cell size.

Placental ischemia induces changes in gene expression in chorionic tissue

Preeclampsia is a serious and common hypertensive complication of pregnancy, affecting ~5 to 8 % of pregnancies. The underlying cause of preeclampsia is believed to be placental ischemia, which causes secretion of pathogenic factors into the maternal circulation. While a number of these factors have been identified, it is likely that others remain to be elucidated. Here, we have utilized a relevant preclinical rodent model of placental ischemia-induced hypertension, the reduced uterine perfusion pressure (RUPP) model, to determine the effect of chronic placental ischemia on the underlying chorionic tissue and placental villi. Tissue from control and RUPP rats were isolated on gestational day 19 and mRNA from these tissues was subjected to microarray analysis to determine differential gene expression. At a statistical cutoff of p < 0.05, some 2,557 genes were differentially regulated between the two groups. Interestingly, only a small subset (22) of these genes exhibited changes of greater than 50 % versus control, a large proportion of which were subsequently confirmed using qRT-PCR analysis. Network analysis indicated a strong effect on inflammatory pathways, including those involving NF-κB and inflammatory cytokines. Of the most differentially expressed genes, the predominant gene classes were extracellular remodeling proteins, pro-inflammatory proteins, and a coordinated upregulation of the prolactin genes. The functional implications of these novel factors are discussed.

Gene expression in hippocampus as a function of differential trait anxiety levels in genetically heterogeneous NIH-HS rats

To identify genes involved in the development/expression of anxiety/fear, we analyzed the gene expression profile in the hippocampus of genetically heterogeneous NIH-HS rats. The NIH-HS rat stock is a unique genetic resource for the fine mapping of quantitative trait loci (QTLs) to very small genomic regions, due to the high amount of genetic recombinants accumulated along more than 50 breeding generations, and for the same reason it can be expected that those genetically heterogeneous rats should be especially useful for studying differential gene expression as a function of anxiety, fearfulness or other complex traits. We selected high- and low-anxious NIH-HS rats according to the number of avoidance responses they performed in a single 50-trial session of the two-way active avoidance task. Rats were also tested in unconditioned anxiety/fearfulness tests, i.e. the elevated zero-maze and a "novel-cage activity" test. Three weeks after behavioral testing, the hippocampus was dissected and prepared for the microarray study. There appeared 29 down-regulated and 37 up-regulated SNC-related genes (fold-change>|2.19|, FDR<0.05) in the "Low-anxious" vs. the "High-anxious" group. Regression analyses (stepwise) revealed that differential expression of some genes could be predictive of anxiety/fear responses. Among those genes for which the present results suggest a link with individual differences in trait anxiety, nine relevant genes (Avpr1b, Accn3, Cd74, Ltb, Nrg2, Oprdl1, Slc10a4, Slc5a7 and RT1-EC12), tested for validation through qRT-PCR, have either neuroendocrinological or neuroinmunological/inflammation-related functions, or have been related with the hippocampal cholinergic system, while some of them have also been involved in the modulation of anxiety or stress-related (neurobiological and behavioral) responses (i.e. Avpr1b, Oprdl1). The present work confirms the usefulness of NIH-HS rats as a good animal model for research on the neurogenetic basis or mechanisms involved in anxiety and/or fear, and suggest that some MHC-(neuroinmunological/inflammation)-related pathways, as well as the cholinergic system within the hippocampus, may play a role in shaping individual differences in trait anxiety.

The prolactin gene: a paradigm of tissue-specific gene regulation with complex temporal transcription dynamics

Transcription of numerous mammalian genes is highly pulsatile, with bursts of expression occurring with variable duration and frequency. The presence of this stochastic or 'noisy' expression pattern has been relatively unexplored in tissue systems. The prolactin gene provides a model of tissue-specific gene regulation resulting in pulsatile transcription dynamics in both cell lines and endocrine tissues. In most cell culture models, prolactin transcription appears to be highly variable between cells, with differences in transcription pulse duration and frequency. This apparently stochastic transcription is constrained by a transcriptional refractory period, which may be related to cycles of chromatin remodelling. We propose that prolactin transcription dynamics result from the summation of oscillatory cellular inputs and by regulation through chromatin remodelling cycles. Observations of transcription dynamics in cells within pituitary tissue show reduced transcriptional heterogeneity and can be grouped into a small number of distinct patterns. Thus, it appears that the tissue environment is able to reduce transcriptional noise to enable coordinated tissue responses to environmental change. We review the current knowledge on the complex tissue-specific regulation of the prolactin gene in pituitary and extra-pituitary sites, highlighting differences between humans and rodent experimental animal models. Within this context, we describe the transcription dynamics of prolactin gene expression and how this may relate to specific processes occurring within the cell.

Expression of proliferin-related protein in testis and the biological significance in testosterone production

Proliferin-related protein (PRP) was originally identified as an angiogenesis inhibitor in mouse placentas. Indeed, the tissue expression of PRP has mainly been documented in placentas. We report herein for the first time that PRP is expressed in male rat testes. Immunocytochemical and in situ hybridization results showed positive PRP immunostaining in Leydig cells. Immunofluorescent staining of PRP in the TM3 Leydig cell line indicates that PRP is located within the cytoplasm. The expression pattern of PRP in rat testis exhibited an age-related increase. HCG significantly up-regulated the level of expression of PRP in TM3 cells via the PKA pathway. To elucidate the function of PRP, experiments were conducted to examine the consequences of lentiviral-mediated RNA interference (RNAi) of PRP on testosterone production and expression of several genes involved in steroidogenesis. PRP silencing caused a decrease in HCG-stimulated testosterone production. In addition, PRP silencing attenuated the increase in PRLR mRNA following HCG stimulation. Moreover, the enhanced effect of PRL on HCG-induced testosterone production was also weakened following PRP silencing, indicating that PRP may be involved in PRL function through an effect on PRL receptor expression in response to stimuli. Taken together, these data suggest that PRP is regulated by HCG and plays roles in male reproduction, such as testosterone production.

Chromosome-substituted rat strains provide insights into the genetics of placentation

The rat possesses a hemochorial form of placentation. Pronounced intrauterine trophoblast cell invasion and vascular remodeling characterize this type of placentation. Strain-specific patterns of placentation are evident in the rat. Some rat strains exhibit deep intrauterine trophoblast invasion and an expanded junctional zone [Holtzman Sprague-Dawley (HSD), Dahl salt sensitive (DSS)], whereas placentation sites of other rat strains are characterized by shallow invasion and a restricted junctional zone [Brown Norway (BN)]. In this report, we identified a quantitative trait that was used to distinguish strain-specific features of rat placentation. Junctional zone prolactin family 5, subfamily a, member 1 (Prl5a1) transcript levels were significantly greater in BN rats than in HSD or DSS rats. Prl5a1 transcript levels were used as a quantitative trait to screen placentation sites from chromosome-substituted rat strains (BN chromosomes introgressed into the DSS inbred strain; DSS-BN panel). Litter size, placental weights, and fetal weights were not significantly different among the chromosome-substituted strains. Regulation of the junctional zone Prl5a1 transcript-level quantitative trait was multifactoral. Chromosome-substituted strains possessing BN chromosomes 14 or 17 introgressed into the DSS inbred rat strain displayed Prl5a1 transcript levels that were significantly different from the DSS pattern and more closely resembled the BN pattern. The in situ placental distribution of Prl5a1 mRNA and the structure of the junctional zone of DSS-BN17 rats mimicked that observed for the BN rat. Prl5a1 gene expression was also assessed in BN vs. HSD trophoblast stem cells and following reciprocal BN and HSD embryo transfer. Strain differences intrinsic to trophoblast and maternal environment were identified. In summary, we have identified chromosomes 14 and 17 as possessing regulatory information controlling a quantitative trait associated with rat placentation.

Molecular cloning and expression of canine prolactin gene

We isolated canine prolactin cDNA from a dog pituitary cDNA library. The 930-bp nucleotide sequence covered the entire open reading frame encoding the putative 229 amino acids. It was located in chromosome 35, and had five exons. The amino acid sequence was highly homologous to the feline and porcine sequences. To generate recombinant canine prolactin, plasmids for full-length canine prolactin were constructed and transfected into the mammalian HEK293 cell line. The recombinant prolactin was secreted into the medium as an N-linked glycosylated (31 kDa) or non-glycosylated (27 kDa) protein. Western blotting revealed both of these bands were canine pituitary protein extracts.

FGF4-dependent stem cells derived from rat blastocysts differentiate along the trophoblast lineage

Differentiated trophoblast cell lineages arise from trophoblast stem (TS) cells. To date such a stem cell population has only been established in the mouse. The objective of this investigation was to establish TS cell populations from rat blastocysts. Blastocysts were cultured individually on a feeder layer of rat embryonic fibroblasts (REFs) in fibroblast growth factor-4 (FGF4) and heparin supplemented culture medium. Once cell colonies were established REF feeder layers could be replaced with REF conditioned medium. The blastocyst-derived cell lines, in either proliferative or differentiated states, did not express genes indicative of ICM-derived tissues. In the proliferative state the cells expressed established stem cell-associated markers of TS cells. Cells ceased proliferation and differentiated when FGF4, heparin, and REF conditioned medium were removed. Differentiation was characterized by a decline of stem cell-associated marker gene expression, the appearance of large polyploid cells (trophoblast giant cells), and the expression of trophoblast differentiation-associated genes. Collectively, the data indicate that the rat blastocyst-derived cell lines not only possess many features characteristic of mouse TS cells but also possess some distinct properties. These rat TS cell lines represent valuable new in vitro models for analyses of mechanisms controlling TS cell renewal and differentiation.

DNA methylation contributes to the tissue-specific expression of the rPL-Iv gene

To understand the tissue-specific expression of the rat placental lactogen-I variant (rPL-Iv) gene, we investigated the methylation pattern of the 5'-flanking region of this gene in various rat tissues. We report that the 5'-flanking region of the rPL-Iv gene was hypomethylated in placenta that expressed the gene and hypermethylated in those tissues that did not express the gene. Moreover, the intron region of the rPL-Iv gene was hypomethylated in the placenta, but hypermethylated in the liver, kidney and pituitary. Although there are 5 CpG sites and the density of CpG dinucleotide is lower within 2 kb of the rPL-Iv 5'-flanking region, the methylated promoter reporter gene produced strong repression in the transcriptional activity of the gene. In addition, the 5'-flanking and intron regions of the rPL-Iv gene were hypomethylated on day 12 of gestation, and the methylation pattern in the placenta remained unchanged from mid-pregnancy until term. The entire genomic region of the rPL-Iv gene might be hypermethylated in tissues other than the placenta, within which its methylated status repress expression of the placenta-specific rPL-Iv gene. Interestingly, the methylation status of the intron region of the rPL-Iv in proliferating Rcho-1 cells was changed to the unmethylated status on day 8 and 12 of differentiation of Rcho-1 cells. These results demonstrate that demethylation in the rPL-Iv upstream region was induced at an early stage of placental development, and once the 5'-flanking region of the rPL-Iv had been demethylated, its status on the rPL-Iv genomic region was continued during pregnancy. Taken together, these results suggest that DNA methylation is responsible for the silencing of tissue-specific genes in non-expressing cells, while defined combinations of trophoblast factors dictate the expression of unmethylated rPL-Iv gene in placenta trophoblast cells.

Prolactin family of the guinea pig, Cavia porcellus

Prolactin (PRL) is a multifunctional hormone with prominent roles in regulating growth and reproduction. The guinea pig (Cavia porcellus) has been extensively used in endocrine and reproduction research. Thus far, the PRL cDNA and protein have not been isolated from the guinea pig. In the present study, we used information derived from the public guinea pig genome database as a tool for identifying guinea pig PRL and PRL-related proteins. Guinea pig PRL exhibits prominent nucleotide and amino acid sequence differences when compared with PRLs of other eutherian mammals. In contrast, guinea pig GH is highly conserved. Expression of PRL and GH in the guinea pig is prominent in the anterior pituitary, similar to known expression patterns of PRL and GH for other species. Two additional guinea pig cDNAs were identified and termed PRL-related proteins (PRLRP1, PRLRP2). They exhibited a more distant relationship to PRL and their expression was restricted to the placenta. Recombinant guinea pig PRL protein was generated and shown to be biologically active in the PRL-responsive Nb2 lymphoma cell bioassay. In contrast, recombinant guinea pig PRLRP1 protein did not exhibit PRL-like bioactivity. In summary, we have developed a new set of research tools for investigating the biology of the PRL family in an important animal model, the guinea pig.

Do molecular signals from the conceptus influence endometrium decidualization in rodents?

A critical period in establishing pregnancy occurs after the onset of implantation but before placental development. Evidence strongly suggests that abnormalities occurring during this period can result in pregnancy termination or in pre-eclampsia; the latter may lead to small-for-gestational-weight offspring that are likely to be unhealthy. Clearly, events occurring in the endometrium during the implantation process are crucial for proper fetal development and for optimal offspring health. In several mammalian species bi-directional communication between the conceptus and endometrium during implantation is required for successful pregnancy. Although different implantation and placentation modes occur in different mammalian species, common aspects of this bi-directional signaling may exist. The molecular signals from the trophoblast cells of the conceptus, which direct endometrial changes during implantation progression, are well known in some nonrodent species. Currently, we know little about such signaling in rodents during implantation progression, when the endometrium undergoes decidualization. This review focuses on data that support the hypothesis that paracrine signals from the rodent conceptus influence decidualization. Where possible, these findings are compared and contrasted with information currently known in other species that exhibit different implantation modes.

Spatial and temporal expression of the 23 murine Prolactin/Placental Lactogen-related genes is not associated with their position in the locus

Background

The Prolactin (PRL) hormone gene family shows considerable variation among placental mammals. Whereas there is a single PRL gene in humans that is expressed by the pituitary, there are an additional 22 genes in mice including the placental lactogens (PL) and Prolactin-related proteins (PLPs) whose expression is limited to the placenta. To understand the regulation and potential functions of these genes, we conducted a detailed temporal and spatial expression study in the placenta between embryonic days 7.5 and E18.5 in three genetic strains.

Results

Of the 22 PRL/PL genes examined, only minor differences were observed among strains of mice. We found that not one family member has the same expression pattern as another when both temporal and spatial data were examined. There was also no correlation in expression between genes that were most closely related or between adjacent genes in the PRL/PL locus. Bioinformatic analysis of upstream regulatory regions identified conserved combinations (modules) of putative transcription factor binding sites shared by genes expressed in the same trophoblast subtype, supporting the notion that local regulatory elements, rather than locus control regions, specify subtype-specific expression. Further diversification in expression was also detected as splice variants for several genes.

Conclusion

In the present study, a detailed temporal and spatial placental expression map was generated for all murine PRL/PL family members from E7.5 to E18.5 of gestation in three genetic strains. This detailed analysis uncovered several new markers for some trophoblast cell types that will be useful for future analysis of placental structure in mutant mice with placental phenotypes. More importantly, several main conclusions about regulation of the locus are apparent. First, no two family members have the same expression pattern when both temporal and spatial data are examined. Second, most genes are expressed in multiple trophoblast cell subtypes though none were detected in the chorion, where trophoblast stem cells reside, or in syncytiotrophoblast of the labyrinth layer. Third, bioinformatic comparisons of upstream regulatory regions identified predicted transcription factor binding site modules that are shared by genes expressed in the same trophoblast subtype. Fourth, further diversification of gene products from the PRL/PL locus occurs through alternative splice isoforms for several genes.

Decidual cells produce a heparin-binding prolactin family cytokine with putative intrauterine regulatory actions

Pregnancy in mice and rats is associated with the production of a large family of hormones/cytokines related to prolactin (PRL). The hormones/cytokines are hypothesized to coordinate maternal and fetal adaptations to pregnancy. In this study, PRL-like protein-J (PLP-J, also known as PRL family 3, subfamily c, member 1 (Prl3c1)) is shown to be a product of the uterine decidua and a regulator of postimplantation intrauterine events. PLP-J-specific antibodies and a series of recombinant PLP-J proteins were generated and used to investigate PLP-J expression and as ligands for investigating biological targets. Decidual PLP-J migrates as a 29-kDa protein and localizes to a band of decidual cells surrounding the trophoblast cell layer on gestation day 8.5. PLP-J ligands specifically bound in situ to the surrounding uterine stromal cells and vasculature within the decidua of gestation day 8.5 implantation sites. We then investigated the in vitro actions of PLP-J on uterine stromal cells and endothelial cells. PLP-J specifically interacted with both cell populations. PLP-J promoted uterine stromal cell proliferation and inhibited endothelial cell proliferation. We determined that PLP-J does not interact with PRL receptors. Instead, PLP-J interacts with heparin-containing molecules, including syndecan-1, which is expressed in gestation day 8.5 pregnant uteri, as well as in uterine stromal cells and endothelial cells. The restricted expression of PLP-J and its specific interactions with uterine stromal cells and endothelial cells suggests that it acts locally and regulates decidual cell development and the endometrial vasculature.

Genomic evolution of the placenta using co-option and duplication and divergence

The invention of the placenta facilitated the evolution of mammals. How the placenta evolved from the simple structure observed in birds and reptiles into the complex organ that sustains human life is one of the great mysteries of evolution. By using a timecourse microarray analysis including the entire lifetime of the placenta, we uncover molecular and genomic changes that underlie placentation and find that two distinct evolutionary mechanisms were utilized during placental evolution in mice and human. Ancient genes involved in growth and metabolism were co-opted for use during early embryogenesis, likely enabling the accelerated development of extraembryonic tissues. Recently duplicated genes are utilized at later stages of placentation to meet the metabolic needs of a diverse range of pregnancy physiologies. Together, these mechanisms served to develop the specialized placenta, a novel structure that led to expansion of the eutherian mammal, including humankind.

Pregnancy and lactation modulate maternal splenic growth and development of the erythroid lineage in the rat and mouse

Maternal physiology changes dramatically during the course of gestation and lactation to meet the needs of the developing fetus and newborn. In the present study, we examined the influence of pregnancy and lactation on growth and erythroid gene expression patterns of the maternal spleen. Holtzman Sprague-Dawley rats and CD-1 mice were killed at various stages of gestation and post partum. We observed pregnancy dependent increases in spleen weight and spleen DNA content in both the rat and mouse. In the rat, spleen size was greatest at the end of pregnancy and regressed post partum. In contrast, mouse spleen size peaked by gestational Day 13 and regressed to its non-pregnant weight before parturition. Pregnancy dependent changes in the size of the spleen were primarily due to an increase in red pulp. Maternal spleen expression of erythroid-associated genes (erythroid Krüppel-like factor, erythroid 5-aminolevulinate synthase-2, β-major globin) was influenced by pregnancy and lactation. A pregnancy dependent increase in erythroid progenitors was also observed. In summary, the demands of pregnancy and lactation cause marked adaptations in the maternal spleen. The maternal spleen increases in size and exhibits an expansion of the erythroid lineage.

Expression and characterization of novel ovine orthologs of bovine placental prolactin-related proteins

Background

The prolactin-related proteins (PRPs) are non-classical placental-specific members of the prolactin/growth hormone family. Among ruminants, they are expressed in the cotyledonary villi of cattle and goat. We investigated placental PRP in sheep in order to gain a comprehensive understanding of the function and evolution of these molecules. We also examined the sequence properties, expression and lactogenic activation of the cloned genes.

Results

We cloned two novel ovine PRPs, named oPRP1 and oPRP2. oPRP2 had a typical PRP sequence similar to bovine PRP1 (bPRP1). oPRP1 had a short sequence identical with bovine or caprine type PRP but the reading frame was shifted. Both oPRPs were expressed in trophoblast giant binucleate cells (BNC) as in cattle and goat. oPRP1 expression declined from the early to the middle stage of gestation. In contrast, oPRP2 expression remained constant throughout the gestation period. oPRP2 was translated to form a mature protein in a mammalian cell expression system. Western blotting showed a molecular mass of 35 kDa for the FLAG-tag fusion oPRP2 protein. This recombinant protein and bPRP1 were bioassayed using Nb2 lymphoma cells; it was confirmed that neither ruminant PRP had lactogenic activity because the Nb2 lymphoma cells did not proliferate.

Conclusion

We have identified two novel PRPs, oPRP1 and oPRP2, in ovine placenta. Both these ovine PRPs were localized and quantitatively expressed in BNC. Absence of lactogenic activity was confirmed for the oPRP2 molecule. It is anticipated that novel and known ruminant PRPs have common functions, except for lactogenic activity.

The prolactin family: effectors of pregnancy-dependent adaptations

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

Gene expression profiles of novel caprine placental prolactin-related proteins similar to bovine placental prolactin-related proteins

Background

This study reports the identification of a full-length cDNA sequence for two novel caprine prolactin-related proteins (cPRP1 and cPRP6), and their localization and quantitative expression in the placenta. Caprine PRPs are compared with known bovine PRPs. We examined their evolution and role in the ruminant placenta.

Results

Full-length cPRP1 and cPRP6 cDNA were cloned with a 717- and 720- nucleotide open-reading frame corresponding to proteins of 238 and 239 amino acids. The cPRP1 predicted amino acid sequence shares a 72% homology with bovine PRP1 (bPRP1). The cPRP6 predicted amino acid sequence shares a 74% homology with bovine PRP6 (bPRP6). The two cPRPs as well as bPRPs were detected only in the placentome by RT-PCR. Analysis by in situ hybridization revealed the presence of both cPRPs mRNA in the trophoblast binucleate cells. These mRNA were quantified by real-time RT-PCR analysis of the placentome at 30, 50, 90 and 140 days of pregnancy. Both new cPRP genes were able to translate a mature protein in a mammalian cell-expression system. Western blotting established the molecular sizes of 33 kDa for cPRP1 with FLAG-tag and 45 kDa for cPRP6 with FLAG-tag. The sequence properties and localized expression of cPRP1 and cPRP6 were similar to those of bovine. However, their expression profiles differed from those in bovine placenta. Although this study demonstrated possible roles of PRPs in caprine placenta, PRPs may regulate binucleate-cell functions like those in bovine, but their crucial roles are still unclear.

Conclusion

We have identified the novel PRPs in caprine placenta. Localization and quantitative expression of caprine PRPs were compared with bovine PRPs. The data indicate that PRP genes in caprine placenta have coordination functions for gestation, as they do in bovine. This is the first study of PRPs function in caprine placenta.

Prolactin-like protein-f subfamily of placental hormones/cytokines: responsiveness to maternal hypoxia

The prolactin (PRL) family of hormones/cytokines is involved in the maintenance of pregnancy and adaptations to physiological stressors. In this report, we identify and characterize a new member of the rat PRL family, examine the impact of maternal hypoxia on placental PRL family gene expression, and investigate maternal adaptive responses to hypoxia. Perusal of the PRL gene family locus in the rat genome resulted in the identification of a putative new member of the rat PRL family. The new member is closely related to the previously reported PRL-like protein-F (PLP-F) and has been named PLP-Fbeta and the originally characterized PLP-F, now termed PLP-Falpha. The two proteins exhibit structural similarities but possess distinct cell- and temporal-specific expression profiles. In vivo hypoxia stimulates placental PLP-Falpha and PLP-E mRNA expression in the rat and mouse, respectively. Rcho-1 trophoblast cells can differentiate into trophoblast giant cells, express PLP-Falpha, and exhibit enhanced PLP-Falpha mRNA levels when cultured under low oxygen tension (2%). Exposure to hypobaric hypoxia during latter part of pregnancy did not significantly impact the expression of PLP-Fbeta mRNA. Finally, exposure to hypobaric hypoxia during midpregnancy led to increased maternal red blood cells, hemoglobin concentrations, hematocrit, and increased concentrations of maternal splenic mRNAs for key proteins involved in hemoglobin synthesis, erythroid Krüppel-like factor, erythroid 5-aminolevulinate synthase-2, and beta-major globin. In summary, adaptive responses to maternal hypoxia include activation of placental PLP-Falpha/E gene expression, which may then participate in maternal hematological adjustments required for maintaining maternal and fetal oxygen delivery.

A uterine decidual cell cytokine ensures pregnancy-dependent adaptations to a physiological stressor

In the mouse, decidual cells differentiate from uterine stromal cells in response to steroid hormones and signals arising from the embryo. Decidual cells are crucially involved in creating the intrauterine environment conducive to embryonic development. Among their many functions is the production of cytokines related to prolactin (PRL), including decidual prolactin-related protein (DPRP). DPRP is a heparin-binding cytokine, which is abundantly expressed in uterine decidua. In this investigation, we have isolated the mouse Dprp gene, characterized its structure and evaluated its biological role. Dprp-null mice were made by replacing exons 2 to 6 of the Dprp gene with an in-frame enhanced green fluorescent protein (EGFP) gene and a neomycin (neo) resistance cassette. Heterozygous intercross breeding of the mutant mice yielded the expected mendelian ratio. Pregnant heterozygote females expressed EGFP within decidual tissue in locations identical to endogenous Dprp mRNA and protein expression. Homozygous Dprp-null mutant male and female mice were viable, exhibited normal postnatal growth rates, were fertile and produced normal litter sizes. A prominent phenotype was observed when pregnant Dprp-null mice were exposed to a physiological stressor. DPRP deficiency interfered with pregnancy-dependent adaptations to hypoxia resulting in pregnancy failure. Termination of pregnancy was associated with aberrations in mesometrial decidual cells, mesometrial vascular integrity, and disruptions in chorioallantoic placenta morphogenesis. The observations suggest that DPRP participates in pregnancy-dependent adaptations to a physiological stressor.