Expression of leukaemia inhibitory factor (LIF) receptor in human placenta: a possible role for LIF in the growth and differentiation of trophoblasts

Preeclampsia is Associated With Reduced ISG15 Levels Impairing Extravillous Trophoblast Invasion

Among several interleukin (IL)-6 family members, only IL-6 and IL-11 require a gp130 protein homodimer for intracellular signaling due to lack of intracellular signaling domain in the IL-6 receptor (IL-6R) and IL-11R. We previously reported enhanced decidual IL-6 and IL-11 levels at the maternal-fetal interface with significantly higher peri-membranous IL-6 immunostaining in adjacent interstitial trophoblasts in preeclampsia (PE) vs. gestational age (GA)-matched controls. This led us to hypothesize that competitive binding of these cytokines to the gp130 impairs extravillous trophoblast (EVT) differentiation, proliferation and/or invasion. Using global microarray analysis, the current study identified inhibition of interferon-stimulated gene 15 (ISG15) as the only gene affected by both IL-6 plus IL-11 vs. control or IL-6 or IL-11 treatment of primary human cytotrophoblast cultures. ISG15 immunostaining was specific to EVTs among other trophoblast types in the first and third trimester placental specimens, and significantly lower ISG15 levels were observed in EVT from PE vs. GA-matched control placentae (p = 0.006). Induction of primary trophoblastic stem cell cultures toward EVT linage increased ISG15 mRNA levels by 7.8-fold (p = 0.004). ISG15 silencing in HTR8/SVneo cultures, a first trimester EVT cell line, inhibited invasion, proliferation, expression of ITGB1 (a cell migration receptor) and filamentous actin while increasing expression of ITGB4 (a receptor for hemi-desmosomal adhesion). Moreover, ISG15 silencing further enhanced levels of IL-1β-induced pro-inflammatory cytokines (CXCL8, IL-6 and CCL2) in HTR8/SVneo cells. Collectively, these results indicate that ISG15 acts as a critical regulator of EVT morphology and function and that diminished ISG15 expression is associated with PE, potentially mediating reduced interstitial trophoblast invasion and enhancing local inflammation at the maternal-fetal interface. Thus, agents inducing ISG15 expression may provide a novel therapeutic approach in PE.

Decidualization of Stromal Cells Promotes Involvement of Mast Cells in Successful Human Pregnancy by Increasing Stem Cell Factor Expression

Decidualization of endometrial stromal cells and the presence of immunocompetent cells, including human mast cells, play important roles in the establishment of pregnancy. In the present study, the effects of decidualization of endometrial stromal cells on the function of decidual mast cells were elucidated. The in vitro assay revealed that decidualization of an endometrial stromal cell line, T HESCs, increased stem cell factor (SCF) mRNA expression. Decidualization of T HESCs enhanced the production of leukemia inhibitory factor (LIF), and the migration of LAD2 cells when co-cultured with T HESCs and LAD2 cells. In addition, decidualization of T HESCs enhanced cell migration in a human trophoblast cell line, HTR-8/SVneo, increased CD9 expression, a marker for extravillous trophoblast (EVT) differentiation, and decreased the secretion of β human chorionic gonadotropin (hCG), a marker for syncytiotrophoblast (ST) differentiation, when co-cultured with T HESCs, LAD2 cells, and HTR-8/SVneo cells, in a LIF-dependent manner. Histological samples from uterine pregnancies, including decidual stromal cells, showed increased SCF mRNA expression, mast cell numbers and LIF mRNA expression thereof compared with tubal pregnancy. SCF produced by decidual stromal cells enhanced the migration and LIF production of mast cells, and promoted the migration and differentiation of trophoblasts to increase the likelihood of successful human pregnancy.

Tacrolimus Improves the Implantation Rate in Patients with Elevated Th1/2 Helper Cell Ratio and Repeated Implantation Failure (RIF)

Introduction An abnormal endometrial immune response is involved in the pathogenesis of repeated implantation failure (RIF), so we investigated the effectiveness of tacrolimus treatment on the endometrium of RIF patients.

Materials and Methods Ten RIF patients with elevated T-helper 1/T-helper 2 (Th1/Th2) cell ratios were recruited into a clinical study. The expression of p53, leukemia inhibitory factor (LIF), interleukin (IL)-4, IL-10, IL-17, and interferon gamma (IFN-γ) in the endometrium of patients with and without tacrolimus treatment and the association of these factors with assisted reproductive technology (ART) outcomes were investigated.

Results Tacrolimus significantly increased the expression of LIF, IL-10, and IL-17 and decreased the expression of IL-4, IFN-γ, and the IFN-γ/IL-10 ratio in RIF patients. Tacrolimus treatment resulted in an implantation rate of 40%, a clinical pregnancy rate of 50%, and a live birth rate of 35% in RIF patients with elevated Th1/Th2 ratios who had previously failed to become pregnant despite at least three transfers of embryos. We also found a significant positive correlation between IL-10 levels and the implantation rate.

Conclusions Our findings suggest that RIF patients with a higher Th1/Th2 ratio could be candidates for tacrolimus therapy and that this immunosuppressive drug could be acting through upregulation of LIF, IL-10, and IL-17.

Molecular Signaling Regulating Endometrium-Blastocyst Crosstalk

Implantation of the embryo into the uterine endometrium is one of the most finely-regulated processes that leads to the establishment of a successful pregnancy. A plethora of factors are released in a time-specific fashion to synchronize the differentiation program of both the embryo and the endometrium. Indeed, blastocyst implantation in the uterus occurs in a limited time frame called the "window of implantation" (WOI), during which the maternal endometrium undergoes dramatic changes, collectively called "decidualization". Decidualization is guided not just by maternal factors (e.g., estrogen, progesterone, thyroid hormone), but also by molecules secreted by the embryo, such as chorionic gonadotropin (CG) and interleukin-1β (IL-1 β), just to cite few. Once reached the uterine cavity, the embryo orients correctly toward the uterine epithelium, interacts with specialized structures, called pinopodes, and begins the process of adhesion and invasion. All these events are guided by factors secreted by both the endometrium and the embryo, such as leukemia inhibitory factor (LIF), integrins and their ligands, adhesion molecules, Notch family members, and metalloproteinases and their inhibitors. The aim of this review is to give an overview of the factors and mechanisms regulating implantation, with a focus on those involved in the complex crosstalk between the blastocyst and the endometrium.

Cell-specific expression and signal transduction of C-C motif chemokine ligand 2 and atypical chemokine receptors in the porcine endometrium during early pregnancy

Chemokines and atypical chemokine receptors (ACKRs; also known as chemokine decoy receptors) play an important role in reproductive immunology by recruiting leukocytes during early pregnancy. The aim of this study was to determine the expression of C-C motif chemokine ligand 2 (CCL2) and ACKRs in the endometrium during estrous cycle and early pregnancy, and to investigate the functional effects of CCL2 on porcine uterine luminal epithelial (pLE) cells. Our results indicated that CCL2, ACKR1, ACKR3, and ACKR4 were strongly detected in the glandular and luminal epithelium of the endometrium during early pregnancy compared to that in non-pregnant pigs. Recombinant CCL2 improved pLE cell proliferation via activation of the PI3K and MAPK pathways and suppression of endoplasmic reticulum (ER) stress by reducing the expression of ER stress regulatory genes. Collectively, these results provide novel insights into CCL2-mediated signaling mechanisms in the porcine endometrium at the maternal-fetal interface during early pregnancy.

Epigenetic changes found in uterine decidual and placental tissues can also be found in the breast cancer microenvironment of the same unique patient: description and potential interpretations

Microenvironmental properties are thought to be responsible for feto-maternal tolerance. Speculatively, ectopic expression of placental gene programs might also be related to cancer cells’ ability to escape from immune vigilance mechanisms during carcinogenesis and cancer progression. Recently, we published the first human genomic evidence of similar immune related gene expression profiles in both placenta (placenta and decidual tissue) and cancer (both primary and metastatic) in the same patient with lymph-node positive breast carcinoma during pregnancy. Here we report the first epigenomic analysis of these tissue samples and describe their main findings, with respect to immune related genes regulation (over or under expressed) in cancer cells with regards placental tissues. We confirm significant similarities, and hierarchical clustering (both unsupervised and supervised), in CpG island methylation patterns between decidual/placental and cancer microenvironments, which cannot be easily explained by simple models or unique pathways. Several different cell types are probably involved in these complex immune regulation mechanisms. Cancers may somehow “hijack” gene programs evolved over millions of years to allow for feto-maternal tolerance in placental mammals in order to escape from immune vigilance and spread locally or to distant sites.

Human Decidual Stromal Cells as a Component of the Implantation Niche and a Modulator of Maternal Immunity

The human decidua is a specialized tissue characterized by embryo-receptive properties. It is formed during the secretory phase of menstrual cycle from uterine mucosa termed endometrium. The decidua is composed of glands, immune cells, blood and lymph vessels, and decidual stromal cells (DSCs). In the process of decidualization, which is controlled by oestrogen and progesterone, DSCs acquire specific functions related to recognition, selection, and acceptance of the allogeneic embryo, as well as to development of maternal immune tolerance. In this review we discuss the relationship between the decidualization of DSCs and pathological obstetrical and gynaecological conditions. Moreover, the critical influence of DSCs on local immune cells populations as well as their relationship to the onset and maintenance of immune tolerance is described.

Association between leukaemia inhibitory factor gene polymorphism and pregnancy outcomes after assisted reproduction techniques

Certain gene polymorphisms are associated with implantation failure and pregnancy loss. Studies of leukaemia inhibitory factor (LIF) gene polymorphisms are scarce. The LIF single nucleotide polymorphism (SNP) thymine (T)/guanine (G) (rs929271) was studied in women to determine whether an association existed with pregnancy outcomes after intracytoplasmic sperm injection (ICSI); 411 women who underwent ICSI were recruited. DNA was extracted from the peripheral blood, and the LIF gene SNP T/G (rs929271) was genotyped using real-time polymerase chain reaction. Participants were divided into three groups according to their LIF genotype: T/T (n = 168), T/G (n = 202) and G/G (n = 41). All IVF and ICSI procedures were carried out under the same clinical and laboratory conditions. The ICSI cumulative results (from fresh plus frozen cycles) of each genotype group were analysed. The G/G genotype in women was associated with a higher implantation rate (T/T: 15.9%, T/G: 16.2%, G/G: 27.0%; P < 0.05), ongoing pregnancy rate/patient (T/T: 31.5%, T/G: 36.1%, G/G: 53.7%; P < 0.05) and ongoing pregnancy rate/transfer (T/T: 18.5%, T/G: 20.2%, G/G: 36.7%; P < 0.05). LIF SNP T/G (rs929271) seems to be a susceptibility biomarker capable of predicting implantation efficiency and pregnancy outcomes.

Prospective assessment of midsecretory endometrial leukemia inhibitor factor expression versus ανβ3 testing in women with unexplained infertility

OBJECTIVE

To evaluate endometrial leukemia inhibitor factor (LIF) expression as a marker of endometrial receptivity in women with unexplained infertility (UI).

DESIGN

Prospective case-control study.

SETTING

University-associated infertility clinics.

PATIENT(S)

Women with UI for more than 1 year and healthy control women.

INTERVENTION(S)

Endometrial biopsy.

MAIN OUTCOME MEASURE(S)

Time to pregnancy was compared between patients with UI who were evaluated for endometrial LIF protein as well as ανβ3 integrin expression. Endometrium was evaluated using immunohistochemistry (IHC) and messenger RNA by real time reverse transcriptase-polymerase chain reaction (PCR) (quantitative real-time reverse transcriptase-PCR) in samples from women with UI as well as healthy control women.

RESULT(S)

Leukemia inhibitor factor was expressed in epithelial cells in a cyclic fashion in controls, and overall expression in the secretory phase was similar between controls and women with UI, whereas ανβ3 integrin expression was reduced. However, using quantitative real-time PCR, LIF messenger RNA abundance was 4.4-fold lower in women with low levels of ανβ3 integrin expression compared with samples with normal integrins. By immunohistochemistry, ανβ3 integrin expression was always lacking when the histology was out of phase, whereas LIF expression was only negative in a subset of those samples. Reduced endometrial LIF expression was strongly associated with poor reproductive outcomes.

CONCLUSION(S)

Endometrial LIF expression peaks in the midsecretory phase and is reduced in some women with UI. The use of LIF in combination with ανβ3 integrin as biomarkers appears to be superior to integrin testing alone when evaluating endometrial receptivity, primarily because of its earlier pattern of expression during the secretory phase.

LIF-STAT signaling and trophoblast biology

Leukemia inhibitory factor (LIF) is a pleiotropic growth factor that regulates several biological functions. This review focuses on the LIF-dependent STAT activation and its impact on modulation of trophoblast functions during embryo implantation. LIF is mainly produced by the maternal endometrium at the time of implantation while its receptors are present both on the endometrium and trophoblasts. It might influence blastocyst attachment through STAT3 activation and expression of integrins. After attachment of the blastocyst, trophoblasts undergo proliferation and differentiation into invasive EVTs and non-invasive STBs. Under in vitro conditions, LIF regulates all these processes through activation of STAT- and MAPK-dependent signaling pathways. The observations that LIF and STAT3 knockout mice are infertile further strengthen the notion about the critical involvement of LIF-mediated signaling during embryo implantation. Hence, a better understanding of LIF-STAT signaling would help in improving fertility as use of LIF in in vitro blastocyst culture improves the implanting ability of blastocyst after IVF.

Interleukin-6 in pregnancy and gestational disorders

IL6 is a multifunctional cytokine with pivotal roles in the inflammatory response and in directing T cell differentiation in adaptive immunity. IL6 is widely expressed in the female reproductive tract and gestational tissues, and exerts regulatory functions in embryo implantation and placental development, as well as the immune adaptations required to tolerate pregnancy. Here, we summarise the current understanding of how membrane-bound and soluble receptors mediate IL6 signalling to regulate leukocytes and non-haemopoietic cells. We review the published literature regarding the expression and actions of IL6 in the uterus, decidua and placenta, and studies implicating this cytokine in pregnancy disorders. Elevated IL6 is frequently evident in the altered cytokine profiles characteristic of unexplained infertility, recurrent miscarriage, preeclampsia and preterm delivery. Notably, there is compelling evidence indicating altered systemic IL6 trans-signalling in women prone to recurrent miscarriage, with excessive IL6 bioavailability potentially inhibiting generation of CD4+ T regulatory cells required for pregnancy tolerance. Insufficient local IL6 may also contribute to fetal loss, since IL6 expression is reduced in the endometrium of women with recurrent miscarriage, and in the fetal-placental tissue of CBA×DBA/2 mice. Consistent with the role of IL6 in key reproductive events, Il6 null mutant mice exhibit elevated fetal resorption and delayed parturition. Investigation of the association between IL6 signalling components and T cell responses in pregnant women, as well as detailed analysis of the maternal immune response in IL6-deficient mice, is now required to define the mechanisms by which this cytokine exerts influence on reproductive success.

A cross-talk of decidual stromal cells, trophoblast, and immune cells: a prerequisite for the success of pregnancy

Embryo implantation and formation of a functional placenta are complex processes that require a plethora of regulatory mechanisms involving both mother and embryo cells. Recently, an important role in this complicated cells and factors network was assigned to the decidual stromal cells (DSC) and trophoblast cells. Decidualization includes biochemical changes that trigger DSC to produce a number of factors required for the implantation and induction of immunotolerance in maternal immune system. Immunotolerance is achieved by a cascade of strictly controlled events starting with selective homing of immune cells to the feto-maternal site, regulated proliferation, and predominant differentiation into a regulatory type of immune cells. Furthermore, cytotoxic effector functions are reduced owing to the influence of steroid hormones, factors, cytokines, and inhibitory receptors. Altogether the entire immune system of the mother is switched to tolerogenic functional state which is a prerequisite for the successful maintenance of pregnancy.

Understanding the link between the IL-6 cytokine family and pregnancy: implications for future therapeutics

Cytokines are involved in almost all processes during the menstrual cycle, the fertilization period and pregnancy. They are expressed in numerous reproduction-related body fluids and tissues. Disorders of cytokine expression patterns may cause pregnancy pathologies. Therefore, cytokines have the potential as new biomarkers in different body compartments for a variety of such pathologies. Furthermore, cytokines may also serve to treat fertility and pregnancy disorders. The IL-6-like family of cytokines is an intensively investigated group of cytokines with well-accepted functions in fertility and pregnancy. This article summarizes current knowledge on IL-6-like cytokines in regard of their role in reproduction and their potential for new strategies in the treatment of reproductive pathologies.

Effects of melanocortins on fetal development

Melanocortins, adrenocorticotropic hormone (ACTH) and α-, β-, and γ-melanocyte-stimulating hormone (MSH) are produced in the placenta and secreted into embryos/fetuses. ACTH concentrations are higher in fetal plasma than in maternal plasma and peak at mid-gestation in rats, whereas ACTH production starts in the anterior lobe of the fetal pituitary at later stages. Melanocortin receptors (MC1-5R), receptors for ACTH and α-, β- and γ-MSH, are expressed in various adult organs. The specific function of these receptors has been well examined in the hypothalamic-pituitary-adrenocortical (HPA) axis and the HPA axis-like network in the skin, and anti-inflammatory effects for white blood cells have also been investigated. MC2R and/or MC5R are also expressed in the testis, lung, kidney, adrenal, liver, pancreas, brain and blood cells at different stages in mouse and rat embryos/fetuses. Melanocortins in embryos and fetuses promote maturation of the HPA axis and also contribute to the development of lung, testis, brain and blood cells. Recently, a unique ACTH function was revealed in fetuses: placental ACTH, which is secreted by the maternal leukemia inhibitory factor (LIF), and induces LIF secretion from fetal nucleated red blood cells. Finally, the maternal LIF-placental ACTH-fetal LIF signal relay regulates the LIF level and promotes neurogenesis in fetuses, which suggests that ACTH acts as a signal transducer or effector for fetal development in the maternal-fetal signal pathway.

Cytokines and Growth Factors in Implantation

Implantation failure is the most important rate limiting factor in the success of assisted reproductive techniques like In vitro fertilization–embryo transfer (IVF-ET). Cytokines are multifunctional signaling molecules having an implicit role in the human implantation process. This review focuses on the redundant roles of cytokines during the various stages of implantation. It also indicates that levels of cytokines in biological fluids like serum and follicular fluid obtained during oocyte retrieval might act as determinants of implantation potential of the blastocyst. Thus a holistic, metabolomic approach of analyzing biological fluids may provide a simpler approach to study the hitherto enigmatic process rather than the proteomic and genomic approach.

Maternal leukemia inhibitory factor (LIF) promotes fetal neurogenesis via a LIF-ACTH-LIF signaling relay pathway

Leukemia inhibitory factor (LIF) promotes the proliferation of neuronal progenitor cells in the cerebrum. However, it remains unclear how fetal LIF level is regulated. Here we show evidence that maternal LIF signals drive fetal LIF levels via the placenta, thereby promoting neurogenesis in the fetal brain in rats. Chronological changes showed that LIF concentration in fetal sera (FS) and fetal cerebrospinal fluid peaked at gestational day (GD) 15.5, after the peak of maternal LIF at GD14.5. LIF injection into rat dams at GD15.5 increased the level of ACTH in FS and subsequently increased LIF levels in FS and fetal cerebrospinal fluid. The elevation of fetal LIF after LIF injection into dams was inhibited by in utero injection of anti-ACTH antibody into fetuses. Cultured syncytiotrophoblasts, which express the LIF receptor and glycoprotein 130, were induced to secrete ACTH and up-regulate Pomc expression by the addition of LIF. Nucleated red blood cells from fetuses at GD15.5, but not GD13.5 or GD17.5, displayed LIF secretion in response to ACTH. Moreover, injection of LIF into dams at GD13.5 or GD17.5 did not result in elevation of ACTH or LIF in fetuses. The labeling index of 5-bromo-2'-deoxyuridine-positive cells in the ventricular zone of the cerebral neocortex increased 24 h after injection of LIF into dams at GD15.5 but not GD13.5 or GD17.5. These results suggest that in rats maternal LIF induces ACTH from the placenta, which in turn induces fetal nucleated red blood cells to secrete LIF that finally increases neurogenesis in fetuses around GD15.

Involvement of transcription factor NR2F2 in human trophoblast differentiation

Background

During the in vitro differentiation of human villous cytotrophoblast (CTB) cells to a syncytiotrophoblast (STB) phenotype, mRNA levels for the nuclear hormone receptor NR2F2 (ARP-1, COUP-TFII) increase rapidly, reaching a peak at day 1 of differentiation that is 8.8-fold greater than that in undifferentiated CTB cells. To examine whether NR2F2 is involved in the regulation of villous CTB cell differentiation, studies were performed to determine whether NR2F2 regulates the expression of TFAP2A (AP-2α), a transcription factor that is critical for the terminal differentiation of these cells to a STB phenotype.

Methodology/Primary Findings

Overexpression of NR2F2 in primary cultures of human CTB cells and JEG-3 human choriocarcinoma cells induced dose-dependent increases in TFAP2A promoter activity. Conversely, siRNA mediated silencing of the NR2F2 gene in villous CTB undergoing spontaneous differentiation blocked the induction of the mRNAs for TFAP2A and several STB cell specific marker genes, including human placental lactogen (hPL), pregnancy specific glycoprotein 1 (PSG1) and corticotropin releasing hormone (CRH) by 51–59%. The induction of TFAP2A promoter activity by NR2F2 was potentiated by the nuclear hormone receptors retinoic acid receptor alpha (RARA) and retinoid X receptor alpha (RXRA).

Conclusions/Significance

Taken together, these results strongly suggest that NR2F2 is involved in villous CTB cell differentiation and that NR2F2 acts, at least in part, by directly activating TFAP2A gene expression and by potentiating the transactivation of TFAP2A by RARA and RXRA.

Leukemia inhibitory factor and interleukin-11: critical regulators in the establishment of pregnancy

Blastocyst implantation into a receptive endometrium is critical to the establishment of pregnancy and is tightly regulated by factors within the blastocyst-endometrial micro-environment. Leukemia inhibitory factor (LIF) and interleukin-11 (IL11) have key roles during implantation. Female mice with a null mutation in the LIF or IL11RA gene are infertile due to a complete failure of implantation or a defective differentiation/decidualization response to the implanting blastocyst, respectively. LIF and IL11 deficiency during pregnancy is associated with infertility and miscarriage in women. Numerous cell populations at the maternal-fetal interface are regulated by LIF/IL11 including the endometrial epithelium, decidualizing stroma, placental trophoblasts and leukocytes. This review focuses on the roles of LIF/IL11 during early pregnancy and highlights their potential as contraceptive targets and therapeutic agents for infertility.

Interleukin-6 stimulates cell migration, invasion and integrin expression in HTR-8/SVneo cell line

Interleukin-6 (IL-6) is present in human endometrium throughout menstrual cycle and in pregnancy. Trophoblast also expresses IL-6. IL-6R and its associated signal transducer gp130 were found in trophoblast as well. IL-6 is generally assumed to be relevant for trophoblast invasion. This study was undertaken to determine influence of endogenous and externally added IL-6 on invasion and migration of first trimester of pregnancy trophoblast in vitro. Integrins alpha(5)beta(1) and alpha(1)beta(1) have been shown to play an important role in trophoblast invasion and the effect of IL-6 on the expression of these integrin subunits was studied. We are showing that in both isolated first trimester of pregnancy cytotrophoblast (CTB) and HTR-8/SVneo cell line IL-6 and IL-6R are present. The effect on migration was studied using cell wounding and migration test on HTR-8/SVneo cells. Effect of IL-6 and function blocking anti-IL-6 antibody in Matrigel invasion tests was studied on both cell types. The effect of IL-6 on integrin subunit expression was determined by cell-based ELISA and Western blot on HTR-8/SVneo cells. The results obtained show that exogenous IL-6 has stimulatory effect on cell migration in HTR-8/SVneo and invasion by both cell types. Function blocking anti-IL-6 inhibited unstimulated invasion by isolated first trimester cytotrophoblast and both cell migration and invasion in unstimulated HTR-8/SVneo. Integrin alpha(5) expression was stimulated by IL-6 to 134% (p<0.05), alpha(1) to 135% (p<0.005), and beta(1) to 134% (p<0.001) of control in cell-based ELISA, but also in Western blot. The data obtained show for the first time sensitivity of extravillous trophoblast cell line HTR-8/SVneo to IL-6, in addition to isolated first trimester cytotrophoblast. We conclude that both exogenous and endogenous IL-6 stimulate trophoblast cell migration and invasion, which may be partly attributable to stimulation of expression of the studied integrin subunits.

Basic aspects of implantation

Implantation, a critical step for establishing pregnancy, requires molecular and cellular events resulting in healthy uterine growth and differentiation, blastocyst adhesion, invasion and placental formation. Successful implantation requires a receptive endometrium, a normal and functional embryo at the blastocyst stage and a synchronized dialogue between maternal and embryonic tissues. In addition to the main role of sex steroids, the complexity of embryo implantation and placentation is exemplified by the number of cytokines and growth factors with demonstrated roles in these processes. Disturbances of the normal expression and action of these cytokines result in absolute or partial failure of implantation and abnormal placental formation in mice and humans. Members of the gp130 cytokine family, interleukin (IL)-11 and leukaemia inhibitory factor, the transforming growth factor-beta superfamily, colony-stimulating factors, and the IL-1 and IL-15 systems are all crucial for successful implantation. In addition, chemokines are important both in recruiting specific cohorts of leukocytes to the implantation site, and in trophoblast trafficking and differentiation. This review provides discussion on embryonic and uterine factors that are involved in the process of implantation in autocrine, paracrine and/or juxtacrine manners at hormonal, cellular, and molecular levels.

Secretory role for human uterodomes (pinopods): secretion of LIF

The differentiation of human endometrial epithelium is a dynamic event, which occurs throughout the menstrual cycle in preparation for pregnancy. The appearance of uterodomes (pinopods) in this regard was first introduced in rodents with an established pinocytotic function, whereas little evidence was available in humans in this context. This study was undertaken to identify the potential physiological roles of uterodomes in the implantation process. To address this, endometrial biopsies from early, mid- and late luteal phases of the menstrual cycle of 23 fertile female patients with regular menses were used. Scanning and transmission electron microscopies (SEM and TEM) as well as immunofluorescence and immunogold TEM were performed to study the morphological changes and the expression pattern of leukaemia inhibitory factor (LIF) at uterodomes. Our results illustrated a high level of LIF expression in the human uterodomes, which was colocalized with the well-known biochemical markers of exocytosis, including syntaxin-1, 25-kDa synaptosomal protein (SNAP-25) and vesicle-associated membrane protein-2 (VAMP-2). Our morphological and immunocytochemical findings illustrated a secretory function for human uterodomes for the first time. In conclusion, this novel function for uterodomes provides an important clue in detection of their physiological function(s) during the process of the plasma membrane transformation.

Cytokines, chemokines and growth factors in endometrium related to implantation

The complexity of the events of embryo implantation and placentation is exemplified by the number and range of cytokines with demonstrated roles in these processes. Disturbance of the normal expression or action of these cytokines results in complete or partial failure of implantation and abnormal placental formation in mice or humans. Of known importance are members of the gp130 family such as interleukin-11 (IL-11) and leukaemia inhibitory factor (LIF), the transforming growth factor beta (TGFbeta) superfamily including the activins, the colony-stimulating factors (CSF), the IL-1 system and IL-15 system. New data are also emerging for roles for a number of chemokines (chemoattractive cytokines) both in recruiting specific cohorts of leukocytes to implantation sites and in trophoblast differentiation and trafficking. This review focuses on those cytokines and chemokines whose expression pattern in the human endometrium is consistent with a potential role in implantation and placentation and for which some relevant actions are known. It examines what is known of their regulation and action along with alterations in clinically relevant situations.

Leukemia inhibitory factor triggers activation of signal transducer and activator of transcription 3, proliferation, invasiveness, and altered protease expression in choriocarcinoma cells

Extravillous trophoblast cells resemble cancer cells with regard to their intrinsic invasiveness. They invade decidual tissue, but, unlike tumor cells, shut down their invasive properties, when they become inappropriate. Stimuli involved in the modulation of invasion, as well as their underlying signaling mechanisms require further clarification. We were especially interested in discovering signals capable of stimulating invasion in otherwise low-invasive cells involved in reproduction. Using the choriocarcinoma cell line Jeg-3 as a model, we have addressed the potential role of cytokine/growth factor-driven activation of signal transducer and activator of transcription 3 (STAT3) in this process. Jeg-3 cells were treated with various factors known to induce trophoblast proliferation, differentiation, migration, or invasiveness (insulin-like-growth-factor-II (IGF-II), hepatocyte growth factor (HGF), interleukin-6 (IL-6), and leukemia inhibitory factor (LIF)). Only LIF elicited strong tyrosine phosphorylation and specific DNA-binding activity of STAT3. It induced a significant acceleration of cell proliferation and promoted the capability of Jeg-3 cells to invade into an artificial extracellular matrix. Moreover, LIF influenced the expression pattern of proteases and protease inhibitors with potential relevance for invasiveness (downregulation of mRNA for tissue inhibitor of metalloproteinase 1 (TIMP-1) and upregulation of mRNA for caspase-4). In conjunction with earlier work, in which we found that STAT3 DNA-binding activity was increased in invasive cells (choriocarcinoma, first trimester trophoblasts) and absent in non-invasive cells (term trophoblasts), these findings suggest a connection between LIF-driven STAT3 activity and invasiveness of choriocarcinoma and trophoblast cells.

Expression of interleukin-11 receptor α and interleukin-11 protein in the endometrium of normal fertile women and women with recurrent miscarriage

Interleukin-11 (IL-11) is a member of the IL-6 family of cytokines. Previous studies have suggested that IL-11 may play a role in human endometrial function. In this study, we have used immunocytochemistry to compare endometrial IL-11Ralpha and IL-11 expression in precisely timed peri-implantation biopsies from 9 normal fertile women and 16 recurrent miscarriage (RM) women. Immunocytochemistry was semi-quantified by obtaining an H-score value, which showed increased expression of both IL-11 and IL-11Ralpha in epithelial cells compared to stromal cells in all biopsies. There was a significant (P<0.01) reduction in epithelial cell IL-11, but not stromal cell IL-11, expression in endometrium from RM women compared to normal fertile women. There were no significant differences in expression of IL-11Ralpha protein in both stromal and epithelial cells in endometrium from the two groups of women. This work shows the presence of IL-11 and IL-11Ralpha within the endometrium of RM women during the peri-implantation period. The decreased expression of IL-11 in epithelial endometrium in RM women suggests that this cytokine may play a role in preventing miscarriage.

Comparison in gene expression of secretory human endometrium using laser microdissection

BACKGROUND

The endometrium prepares for implantation under the control of steroid hormones. It has been suggested that there are complicated interactions between the epithelium and stroma in the endometrium during menstrual cycle. In this study, we demonstrate a difference in gene expression between the epithelial and stromal areas of the secretory human endometrium using microdissection and macroarray technique.

METHODS

The epithelial and stromal areas were microdissected from the human endometrium during the secretory phase. RNA was extracted and amplified by PCR. Macroarray analysis of nearly 1000 human genes was carried out in this study. Some genes identified by macroarray analysis were verified using real-time PCR.

RESULTS

In this study, changes in expression <2.5-fold in three samples were excluded. A total of 28 genes displayed changes in expression from array data. Fifteen genes were strongly expressed in the epithelial areas, while 13 genes were strongly expressed in the stromal areas. The strongly expressed genes in the epithelial areas with a changes >5-fold were WAP four-disulfide core domain 2 (44.1 fold), matrix metalloproteinase 7 (40.1 fold), homeo box B5 (19.8 fold), msh homeo box homolog (18.8 fold), homeo box B7 (12.7 fold) and protein kinase C, theta (6.4 fold). On the other hand, decorin (55.6 fold), discoidin domain receptor member 2 (17.3 fold), tissue inhibitor of metalloproteinase 1 (9 fold), ribosomal protein S3A (6.3 fold), and tyrosine kinase with immunoglobulin and epidermal growth factor homology domains (5.2 fold) were strongly expressed in the stromal areas. WAP four-disulfide core domain 2 (19.4 fold), matrix metalloproteinase 7 (9.7-fold), decorin (16.3-fold) and tissue inhibitor of metalloproteinase 1 (7.2-fold) were verified by real-time PCR.

CONCLUSIONS

Some of the genes we identified with differential expression are related to the immune system. These results are telling us the new information for understanding the secretory human endometrium.

Endometrial glands as a source of nutrients, growth factors and cytokines during the first trimester of human pregnancy: a morphological and immunohistochemical study

BACKGROUND

The maternal circulation to the human placenta is not fully established until 10-12 weeks of pregnancy. During the first trimester the intervillous space is filled by a clear fluid, in part derived from secretions from the endometrial glands via openings in the basal plate. The aim was to determine the activity of the glands throughout the first trimester, and to identify components of the secretions.

METHODS

Samples of human decidua basalis from 5-14 weeks gestational age were examined by transmission electron microscopy and immunohistochemically. An archival collection of placenta-in-situ samples was also reviewed.

RESULTS

The thickness of the endometrium beneath the implantation site reduced from approximately 5 mm at 6 weeks to 1 mm at 14 weeks of gestation. The glandular epithelium also transformed from tall columnar cells, packed with secretory organelles, to a low cuboidal layer over this period. The lumens of the glands were always filled with precipitated secretions, and communications with the intervillous space could be traced until at least 10 weeks. The glandular epithelium reacted strongly for leukaemia inhibitory factor, vascular endothelial growth factor, epidermal growth factor, transforming growth factor beta, alpha tocopherol transfer protein, MUC-1 and glycodelin, and weakly for lactoferrin. As gestation advanced uterine natural killer cells became closely approximated to the basal surface of the epithelium. These cells were also immunopositive for epidermal growth factor.

CONCLUSIONS

Morphologically the endometrial glands are best developed and most active during early human pregnancy. The glands gradually regress over the first trimester, but still communicate with the intervillous space until at least 10 weeks. Hence, they could provide an important source of nutrients, growth factors and cytokines for the feto-placental unit. The endometrium may therefore play a greater role in regulating placental growth and differentiation post-implantation than previously appreciated.

Growth-associated gene expression profiles by microarray analysis of trophoblast of molar pregnancies and normal villi

We used microarray analysis to investigate expression profiles of 589 known genes committed to cell growth control to characterize regulatory circuitry for cell proliferation in complete moles (CMs). CMs are characterized by hyperplastic trophoblast and have a high propensity to give rise to choriocarcinoma. Characteristic alterations in gene expression profiles were observed when compared with normal villi. Fifty-seven genes were significantly up-regulated in CMs and involved the Ras-Map kinase 3, Jak-STAT5, and Wnt signal pathways, implicating growth factor or cytokine-mediated signal pathways in the trophoblastic hyperplasia of CMs. Several genes associated with anti-apoptosis, cell structuring, and/or cell attachment were also up-regulated in CMs. In contrast, relatively fewer genes were down-regulated and these involved IGFBPs, versican, interleukin-1, tumor necrosis factor receptor, CD44, and RAD52. Genes identified in this study may elucidate regulation mechanisms of trophoblastic proliferation and mechanisms causing a pathological phenotype in CMs.

Tolerance to the foeto-placental 'graft': ten ways to support a child for nine months

Tolerance to the foetal 'allograft' has been extensively studied in the past few years, providing interesting new insights. In addition to a potential role for HLA-G, which has been widely discussed, there are hypotheses suggesting roles for several other molecules or cells: leukemia inhibitory factor and its receptor; indoleamine 2. 3-dioxygenase; the Th1/Th2 balance; suppressor macrophages; hormones such as progesterone or the placental growth hormone; CD95 and its ligand; and, as recently proposed, annexin II. Tolerance of the foetal allograft is probably the consequence of a wide panel of mechanisms that may or may not be pregnancy-specific, that are of major or secondary importance and that may be interconnected.

Changes in uterine expression of leukemia inhibitory factor receptor gene during pregnancy and its up-regulation by prolactin in the western spotted skunk

The multifunctional cytokine leukemia inhibitory factor (LIF) is presumed to participate in preparing the uterus for blastocyst implantation. Increased production of LIF is positively correlated with termination of embryonic diapause and preparation for implantation in the spotted skunk. This study examined changes in the expression, localization, and hormonal regulation of LIF receptor (LIFRbeta) gene expression in the uterus of the skunk. Changes in the uterine concentration of LIFRbeta mRNA during pregnancy or in response to hormones after ovariectomy were determined by Northern hybridization analysis and reverse-transcriptase polymerase chain reaction. The skunk uterus produces two LIFRbeta transcripts, the levels of which increase in concentration when the blastocysts resume their development but then decline somewhat during the latter stage of blastocyst activation. Ovariectomy significantly reduced uterine LIFRbeta expression. Estradiol and/or progesterone failed to significantly elevate LIFRbeta mRNA levels in ovariectomized animals. Prolactin significantly increased uterine concentrations of LIFRbeta mRNA to greater than those of ovariectomized controls, but these levels were not comparable to those observed during preimplantation. The LIFRbeta mRNA was predominately localized to stromal cells surrounding the uterine glands and in yolk sac endoderm, syncytiotrophoblast, and cytotrophoblast of postimplantation embryos.

Leukemia-inhibitory factor-neuroimmune modulator of endocrine function

Leukemia-inhibitory factor (LIF) is a pleiotropic cytokine expressed by multiple tissue types. The LIF receptor shares a common gp130 receptor subunit with the IL-6 cytokine superfamily. LIF signaling is mediated mainly by JAK-STAT (janus-kinase-signal transducer and activator of transcription) pathways and is abrogated by the SOCS (suppressor-of cytokine signaling) and PIAS (protein inhibitors of activated STAT) proteins. In addition to classic hematopoietic and neuronal actions, LIF plays a critical role in several endocrine functions including the utero-placental unit, the hypothalamo-pituitary-adrenal axis, bone cell metabolism, energy homeostasis, and hormonally responsive tumors. This paper reviews recent advances in our understanding of molecular mechanisms regulating LIF expression and action and also provides a systemic overview of LIF-mediated endocrine regulation. Local and systemic LIF serve to integrate multiple developmental and functional cell signals, culminating in maintaining appropriate hormonal and metabolic homeostasis. LIF thus functions as a critical molecular interface between the neuroimmune and endocrine systems.

Uterine leukocytes: key players in pregnancy

In species with hemochorial placentation, which includes humans, mice and rats, antigen-specific T and B lymphocytes which are responsible for acquired immunity are virtually absent from the maternal-fetal interface. In contrast, non-antigen specific natural killer cells and macrophages which provide innate immunity are abundant and highly specialized. Autocrine/paracrine factors such as steroid and polypeptide hormones, prostaglandins and anti-inflammatory cytokines that are present in the uterine environment during pregnancy re-program their secretory profiles. Recent studies using transgenic mice and other approaches indicate that these environmentally modified leukocytes have major pregnancy-associated functions that include facilitation of implantation, modulation of the maternal uterine vasculature, supply of growth factors to the placenta, promotion of trophoblast differentiation and facilitation of parturition.

Embryo-maternal interactions at the implantation site: a delicate equilibrium

Blastocyst implantation and successful establishment of pregnancy require delicate interactions between the embryo and the maternal environment. During preimplantation, maternal/embryo communication is mediated by the trophectoderm. In the late luteal phase, physiological changes occur in the endometrium to allow blastocyst implantation. The "window of implantation" represents the period of maximum uterine receptivity for implantation. In response to signals from the embryo, pregnancy-specific proteins are released in maternal serum and a series of morphological, biochemical and immunological changes occur in the uterine environment. These systemic and local modifications can be considered to constitute "the maternal recognition of pregnancy". The human hemochorial placenta arises primarily through proliferation, migration and invasion of the endometrium and its vasculature by the embryonic trophoblast. The complex invasive processes accompanying implantation of the embryo are controlled at the embryo-maternal interface by factors from decidualized endometrium and the trophoblast itself. An inflammatory reaction and a proper maternal immune response allow survival and development of the feto-placental unit. In this review, we focus on interactions between trophoblast and uterine tissues and on cellular mechanisms and molecular signals involved in the closely regulated process of implantation.

Functional map of a placenta-specific enhancer of the human leukemia inhibitory factor receptor gene

We recently reported a placenta-specific enhancer in the human leukemia inhibitory factor receptor (LIFR) gene and now show detailed characterization of the 226-base pair enhancer (-4625/-4400 nucleotides). Four of twenty-two mutants in linker analysis showed reduced promoter activities to 45, 30, 10, and 10%, respectively. Specific binding of region A (-4617/-4602) with nuclear extract was competed by a known Oct-1 oligo and supershifted by Oct-1 antibody. Specific binding of region B (-4549/-4535) was competed by a GATA oligo, but could not be supershifted by four GATA antibodies. Nevertheless, mutagenesis showed that critical bases in region B were identical to the GATA core motif, indicating that region B may bind to a novel GATA family transcription factor. The other two adjacent regions designated as region C (-4464/-4445) showed no known consensus binding sites, and their specific placental JEG-3 nuclear extract binding was not evident in nonplacental nuclear extracts and was not competed by a trophoblast specific element (TSE), indicating that region C is a novel placenta-specific element (PSE, CATTTCCTGAACTAGTTTTT). Footprinting localized the binding boundary of PSE-binding protein (PSEB), and three Gs were found to be important for specific PSE binding. UV cross-linking showed that PSEB had a molecular mass of approximately 160 kDa, substituting the PSE with two previously reported placenta elements TSE or chorionic somatomammotropin enhancer factor 1 (CSEF-1) motifs resulted in markedly different promoter activities, indicating that PSEB is indeed different from TSE binding protein or CSEF-1. These results are the first demonstration that a novel PSE is the major element for placenta-specific enhancer activity in human LIFR gene.

Cloning of leukemia inhibitory factor (LIF) and its expression in the uterus during embryonic diapause and implantation in the mink (Mustela vison)

Leukemia inhibitory factor (LIF) is essential for embryo implantation in mice. Whether LIF plays a role in termination of embryonic diapause and initiation of implantation in carnivores, especially in species with obligate delayed implantation such as the mink, is not known. The objectives of this study were to clone the LIF coding sequence in the mink and determine its mRNA abundance in the uterus through embryonic diapause, implantation, and early postimplantation. We show that the mink LIF cDNA contains 609 nt encoding a deduced protein of 203 amino acids. The homologies are 80.6, 90, 88.2, 87.6, and 86.8% in coding sequence and 79.2, 90.1, 91, 90.1 and 85.4% in amino acid sequence with mouse, human, pig, cow, and sheep respectively. Glycosylation sites and disulfide bonds present in other species are generally conserved in the mink LIF sequence. Quantitation by polymerase chain reaction amplification indicates that LIF mRNA is expressed in mink uterus just prior to implantation and during the first two days after implantation, but not during diapause or later after implantation pregnancy. The abundance of LIF mRNA was significantly higher in the uterus at the embryo expansion stage (P < 0.05) than at days 1-2 of postimplantation. By immunohistochemical localization it was shown that LIF is expressed in the uterine epithelial glands at time of embryonic expansion and in early postimplantation. The coincidence of LIF expression with implantation in this species suggests that LIF is involved in the implantation process, and may be a maternal signal which terminates obligate embryonic diapause.

Defective production of both leukemia inhibitory factor and type 2 T-helper cytokines by decidual T cells in unexplained recurrent abortions

Leukemia inhibitory factor is essential for embryo implantation, and a shift from type 1 T-helper to type 2 T-helper response at the fetal-maternal interface may contribute to successful pregnancy. We show that LIF production is associated with type 2 T-helper cells, is upregulated by IL-4 and progesterone and is downregulated by IL-12, IFN-gamma and IFN-alpha. We also show a decreased production of LIF, IL-4 and IL-10 by decidual T cells of women with unexplained recurrent abortions in comparison with that of women with normal gestation. The defective production of LIF and/or type 2 T-helper cytokines may contribute to the development of unexplained recurrent abortions.

Effect of human chorionic gonadotropin on cytokine production from human endometrial cells in vitro

PROBLEM

To examine whether human chorionic gonadotropin (hCG) is involved in the regulation of interleukin (IL)-6, tumor necrosis factor (TNF)-alpha, and leukemia inhibitory factor (LIF) secretion from cultured human endometrial cells.

METHOD OF STUDY

A mixed population of endometrial cells from six in vitro fertilization/embryo transfer patients was cultured and incubated with various doses of hCG (0, 1, 10, 50, 100, and 500 IU/ml) for 24 hr. IL-6, TNF-alpha, and LIF levels in the culture medium were measured with enzyme-linked immunosorbent assay.

RESULTS

IL-6 and TNF-alpha levels were stimulated by hCG in a dose-dependent manner. Stimulation of IL-6 and TNF-alpha levels by 500 IU/ml of hCG increased their production by 3.7- and 2.8-fold, respectively (P < 0.05). Stimulation of IL-6 by 100 IU/ml of hCG was also significant (P < 0.05). However, there was no significant effect of hCG on LIF secretion by endometrial cells (P = 0.31).

CONCLUSIONS

hCG is involved in the regulation of endometrial cytokine production from human endometrial cells in vitro. This finding supports the recently emerging notion that hCG could have important local roles within the uterus besides its well-known luteotrophic role on the corpus luteum for maintenance of pregnancy.

Leukemia inhibitory factor in human reproduction

PROBLEM

Leukemia inhibitory factor (LIF) is a pleiotropic cytokine of the interleukin-6 family and has different biological actions in various tissue systems. Although named for its ability to inhibit proliferation of a myeloid leukemic cell line by inducing differentiation, it also regulates the growth and differentiation of embryonic stem cells, primordial germ cells, peripheral neurons, osteoblasts, adipocytes, and endothelial cells. LIF is crucial for successful implantation of the embryo in mice. Currently, there is an accumulation of data about the role of LIF in human reproduction.

METHOD OF STUDY

This review of the literature and of our studies focuses on the expression, regulation, and effects of LIF in the human endometrium, fallopian tube, and ovarian follicle.

RESULTS

Human endometrium expresses LIF in a menstrual cycle-dependent manner. Maximal expression is observed between days 19 and 25 of the menstrual cycle, coinciding with the time of implantation. Various cytokines and growth factors induce endometrial LIF expression in vitro. LIF receptor is expressed in endometrial tissue throughout the menstrual cycle and on human blastocysts in a stage-dependent manner. Affecting the trophoblast differentiation pathway toward the adhesive phenotype, LIF plays a role in implantation. LIF is also expressed and secreted by the epithelial cells of the fallopian tube. Its increased expression in the tubal stromal cell cultures by the inflammatory cytokines suggests a link between salpingitis and ectopic implantation in the tube. The rising follicular fluid LIF level around the time of ovulation indicates that LIF may play a role in ovulatory events, early embryonic development, and implantation.

CONCLUSIONS

There is growing evidence that LIF may be one of the entities that plays a role in human reproduction.

Leukemia inhibitory factor (LIF) production by human decidua and its relationship with pregnancy hormones

The expression of leukemia inhibitory factor (LIF) by murine uterus was shown to be regulated by maternal hormones and was not dependent on the presence of an embryo. The objective of this study was to investigate whether in humans the secretion of LIF during early pregnancy is under maternal control and whether its production is correlated with pregnancy hormones, progesterone and beta-human chorionic gonadotropin (beta hCG). To exclude the possibility of paracrine interaction of decidua with trophoblast, we examined the secretion of LIF in women with extrauterine pregnancy. The present study was designed as a prospective, blinded, clinical and immunobiochemical study. The endometrial biopsies were performed on 12 women during surgery for ectopic pregnancy. On the same day, the level of progesterone and beta hCG in maternal plasma was examined. LIF concentration was determined in supernatants taken from cultured decidual explants. LIF production by decidual culture explants was found in all women with an ectopic pregnancy (Median 5015 pg, range 1389-19,304 pg). There was no correlation between the LIF production and the term of pregnancy, or with the level of circulated beta hCG (p > 0.05). However, when the concentration of progesterone in circulating plasma was less than 5 ng/ml, the secretion of LIF was 2.3-fold higher as compared to women who had progesterone levels of more than 5 ng/ml (p < 0.01). Therefore, we conclude that LIF is actively produced by human decidua and that the production of this cytokine does not depend on the presence of fetotrophoblast. This study demonstrates for the first time that progesterone downregulates the secretion of LIF in the decidua during early pregnancy.

Identification of an upstream enhancer within a functional promoter of the human leukemia inhibitory factor receptor gene and its alternative promoter usage

Knockout of the leukemia inhibitory factor receptor (LIFR) gene results in disrupted placental architecture, imbalanced bone development, and losses of functional neurons. We here report the identification of an enhancer in a functional human LIFR gene promoter and alternative promoter usage by this gene. A single transcription start site was identified in placental JEG-3 cells and a genomic clone containing 4876-nucleotide upstream sequences was found to have promoter activity in JEG-3 cells. However, in osteogenic sarcoma U-2 OS cell, Northern blot using a probe of the first exon detected in JEG-3 cells failed to detect LIFR transcripts. 5'-Rapid amplification of cDNA ends (RACE) revealed an alternative first exon and a 0.6-kilobase pair (kb) 5'-flanking region possessed promoter activity in U-2 OS cells. For the 4.8-kb promoter active in placental cells, a minimal promoter was localized within -162 nucleotides. Three regions increased and one inhibited promoter activity. Subcloning of an activation region (-4876 to -3453 nucleotides) into SV40 promoter either upstream or downstream in either orientation to the luciferase reporter resulted in 10-35-fold luciferase induction, demonstrating the characteristics of an enhancer. Transfections into nine cell lines of different tissue origin indicated that the cloned promoter and enhancer in the 4.8-kb fragment was placental tissue-specific. A 226-base pair fragment (-4625 to -4400 nucleotides) was further localized as the minimal enhancer region, in which deletion of either element A (-4625 to -4581 nucleotides) or element B (-4418 to -4400 nucleotides) resulted in the loss of enhancer activity. Electrophoretic mobility shift assay confirmed that these two elements bind to specific nuclear proteins individually. In the middle region between element A and B, disruption of enhancer integrity also led to a loss of enhancer activity, although two SP1 and three NF-kappaB/c-Rel binding sites did not contribute to enhancer function. These results demonstrate a complex regulation of the human LIFR gene, including alternative promoter usage and tissue-specific elements at the transcription level.

Complementary tissue-specific expression of LIF and LIF-receptor mRNAs in early mouse embryogenesis

The maintenance of pluripotential embryonic stem (ES) cells is dependent on the cytokine LIF. This report documents the mRNA expression profiles of LIF and the two components of the LIF-receptor complex, LIF-R and gp130, during early mouse embryogenesis. These mRNAs were undetectable in 1- or 2-cell embryos, but all were present by the blastocyst stage. LIF transcripts were localised in the differentiated trophectoderm, and were absent from the pluripotential inner cell mass. In contrast, LIF-R mRNA was found in the inner cell mass but not in the trophectoderm. This complementary pattern of expression is suggestive of a paracrine coupling between stem cells and differentiated progeny at the earliest stage of mammalian development. After implantation, transcripts for all components were down-regulated in the embryo. High levels of LIF-R and gp130 mRNAs were observed in the deciduum, however. These dynamic, tissue-specific expression patterns are consistent with regulatory roles for LIF or related cytokines, both in the maintenance of pluripotency in the mouse embryo, and in development of the foeto-maternal interface.