Presence of leukaemia inhibitory factor and interleukin 6 in porcine uterine secretions prior to conceptus attachment

The uterine secretome initiates growth of gynecologic tissues in ectopic locations

Endosalpingiosis (ES) and endometriosis (EM) refer to the growth of tubal and endometrial epithelium respectively, outside of their site of origin. We hypothesize that uterine secretome factors drive ectopic growth. To test this, we developed a mouse model of ES and EM using tdTomato (tdT) transgenic fluorescent mice as donors. To block implantation factors, progesterone knockout (PKO) tdT mice were created. Fluorescent lesions were present after oviduct implantation with and without WT endometrium. Implantation was increased (p<0.05) when tdt oviductal tissue was implanted with endometrium compared to oviductal tissue alone. Implantation was reduced (p<0.0005) in animals implanted with minced tdT oviductal tissue with PKO tdT endometrium compared to WT endometrium. Finally, oviductal tissues was incubated with and without a known implantation factor, leukemia inhibitory factor (LIF) prior to and during implantation. LIF promoted lesion implantation. In conclusion, endometrial derived implantation factors, such as LIF, are necessary to initiate ectopic tissue growth. We have developed an animal model of ectopic growth of gynecologic tissues in a WT mouse which will potentially allow for development of new prevention and treatment modalities.

Novel insights into conceptus-maternal signaling during pregnancy establishment in pigs

Pregnancy establishment in mammals, including pigs, requires coordinated communication between developing conceptuses (embryos with associated membranes) and the maternal organism. Porcine conceptuses signalize their presence by secreting multiple factors, of which estradiol-17β (E2) is considered the major embryonic signal initiating the maternal recognition of pregnancy. During this time, a limited supply of prostaglandin (PGF2α) to the corpora lutea and an increased secretion of luteoprotective factors (e.g., E2 and prostaglandin E2 [PGE2]) lead to the corpus luteum's maintained function of secreting progesterone, which in turn primes the uterus for implantation. Further, embryo implantation is related to establishing an appropriate proinflammatory environment coordinated by the secretion of proinflammatory mediators including cytokines, growth factors, and lipid mediators of both endometrial and conceptus origin. The novel, dual role of PGF2α has been underlined. Recent studies involving high-throughput technologies and sophisticated experimental models identified a number of novel factors and revealed complex relationships between these factors and those already established. Hence, it seems that early pregnancy should be regarded as a sequence of processes orchestrated by pleiotropic factors that are involved in redundancy and compensatory mechanisms that preserve the essential functions critical for implantation and placenta formation. Therefore, establishing the hierarchy between all molecules present at the embryo-maternal interface is now even more challenging.

STAT3 in porcine endometrium during early pregnancy induces changes in extracellular matrix components and promotes angiogenesis†

A molecular interaction between maternal endometrium and implanting conceptus can lead to activation of a variety of transcription factors that regulate expression of several genes necessary for the process of embryo implantation. While, signal transducer and activator of transcription 3 (STAT3) is responsible for decidualization and epithelial remodeling in humans and mice, its role in porcine endometrium has not been explored before. In the present study, we observed a pregnancy dependent increase in gene and protein expression of STAT3. Phosphorylated STAT3 was predominantly present in the endometrium of pregnant animals in luminal and glandular epithelium and in the endothelium of blood vessels with a weak staining in stromal cells. Interleukins, IL-1β and IL-6, and epidermal growth factor (EGF)-induced STAT3 expression and phosphorylation in endometrial explants collected on Day 13 of the estrous cycle. Biological significance of STAT3 was evaluated by blocking its phosphorylation with STAT3-specific inhibitor, Stattic. Using porcine extracellular matrix (ECM) and adhesion molecule array, EGF was shown to induce changes in gene expression of ECM components: MMP1, MMP3, MMP12, LAMA1, SELL, and ICAM1, which was abrogated in the presence of Stattic. Transcriptional activity of STAT3 was observed in promoter regions of MMP3 and MMP12. Additionally, IL-6-induced STAT3 phosphorylation upregulated VEGF and VCAM1 abundances in endometrial-endothelial cells (EEC). Moreover, IL-6 resulted in an increase in EEC proliferation and capillary formation which was reversed in the presence of Stattic. Results of present study reveal a role for STAT3 phosphorylation in regulating extracellular matrix remodeling and angiogenesis in porcine endometrium to facilitate embryo implantation.

Transcriptome regulation of extracellular vesicles derived from porcine uterine flushing fluids during peri-implantation on endometrial epithelial cells and embryonic trophoblast cells

The extracellular vesicles (EVs) in uterine fluids play a vital role in embryo implantation by mediating intrauterine communication between conceptus and maternal endometrium in pigs. However, the regulatory mechanism of EVs in uterine fluids is largely unclear. In order to understand the effect of EVs in uterine flushing fluids (UFs) during embryo implantation on endometrial epithelial cells (EECs) and embryonic trophoblast cells (PTr2 cells). The UFs-EVs on day 13 of pregnancy (D13) were added to the culture medium of EECs and PTr2 cells. It was found that PKH-67 labeled UFs-EVs could be taken up in EECs and PTr2 cells. Transcriptome sequencing analysis showed that a total of 1793 and 6279 genes were differentially expressed in the EECs and PTr2 cells after the treatment of UFs-EVs on D13, respectively. Among these genes, real-time quantitative PCR (RT-qPCR) results indicated that ID2, ITGA5, CXCL10 and CXCL11 genes were differentially expressed in both EECs and PTr2 cells after treatment. Bioinformatics analysis showed that the differentially expressed (DE) genes in EECs and PTr2 cells after treatment are involved in immune regulation, cell migration, cell adhesion and the secretion and uptake of EVs. Our research offers novel insight into the regulation mechanism of UFs-EVs on D13 in EECs and PTr2 cells.

Local action of cytokines and immune cells in communication between the conceptus and uterus during the critical period of early embryo development, attachment and implantation - Implications for embryo survival in cattle: A review

Early embryo development, implantation and pregnancy involve a complex dialogue between the embryo and mother. In cattle this dialogue starts as early as days 3-4 when the embryo is still in the oviduct, and it continues to implantation. Immunological processes involving cytokines, mast cells and macrophages form an important part of this dialogue. Amongst the cytokines, interleukin-6 (Il-6) and leukemia inhibitory factor (LIF) are secreted by both the embryo and uterine endometrium and form part of an ongoing and reciprocating dialogue. Mast cells and macrophages populate the uterine endometrium during embryo development and are involved in achieving the correct balance between inflammatory and anti-inflammatory reactions at the uterus that are associated with embryo attachment and implantation. Embryo loss is the major cause of reproductive wastage in cattle, and livestock generally. A deeper understanding of immunological processes during early embryo development will help to achieve the next step change in the efficiency of natural and assisted breeding.

Allogeneic Embryos Disregulate Leukemia Inhibitory Factor (LIF) and Its Receptor in the Porcine Endometrium During Implantation

Despite its advantages for pig breeding, embryo transfer (ET) has a major handicap: high embryo mortality during the pre- and implantation period, probably caused by divergent phenomena of tolerance between the immunologically unrelated (i.e., allogeneic) embryos and the recipient sow. Thus, to reach a similar maternal tolerance as in conventional breeding by artificial insemination (AI) would be the key to ET-success. For this reason, we studied the expression of the leukemia inhibitory factor (LIF) cytokine and its receptor in the pig endometrium during the implantation period (days 18 and 24) in sows subjected to ET (AL group) vs. post-cervical-AI controls (Hemi-AL group). Quantification of expression was performed at both mRNA (rt-qPCR) and protein (WB) levels. The expression of endometrial LIF on day 24 was considerably lower in ET than in AI pregnancies. Correlations between endometrial mRNA levels of LIF and LIF-R showed that, contrary to early AI-pregnancies, ET-pregnancies lack an inverse relation between cytokine and receptor levels. In conclusion, ET-pregnancies lack sufficient endometrial levels of LIF to develop adequate immunotolerance mechanisms to prevent the rejection of allogeneic ET-embryos.

The In Vitro Effect of Prostaglandin E2 and F2α on the Chemerin System in the Porcine Endometrium during Gestation

Chemerin belongs to the group of adipocyte-derived hormones known as adipokines, which are responsible mainly for the control of energy homeostasis. Adipokine exerts its influence through three receptors: Chemokine-like receptor 1 (CMKLR1), G protein-coupled receptor 1 (GPR1), and C-C motif chemokine receptor-like 2 (CCRL2). A growing body of evidence indicates that chemerin participates in the regulation of the female reproductive system. According to the literature, the expression of chemerin and its receptors in reproductive structures depends on the local hormonal milieu. The aim of this study was to investigate the in vitro effect of prostaglandins E2 (PGE2) and F2α (PGF2α) on chemerin and chemerin receptor (chemerin system) mRNAs (qPCR) and proteins (ELISA, Western blotting) in endometrial tissue explants collected from early-pregnant gilts. Both PGE2 and PGF2α significantly influenced the expression of the chemerin gene, hormone secretion, and the expression of chemerin receptor genes and proteins. The influence of both prostaglandins on the expression of the chemerin system varied between different stages of gestation. This is the first study to describe the modulatory effect of PGE2 and PGF2α on the expression of the chemerin system in the porcine uterus during early gestation.

Spatial organization of endometrial gene expression at the onset of embryo attachment in pigs

BACKGROUND

During the preimplantation phase in the pig, the conceptus trophoblast elongates into a filamentous form and secretes estrogens, interleukin 1 beta 2, interferons, and other signaling molecules before attaching to the uterine epithelium. The processes in the uterine endometrium in response to conceptus signaling are complex. Thus, the objective of this study was to characterize transcriptome changes in porcine endometrium during the time of conceptus attachment considering the specific localization in different endometrial cell types.

RESULTS

Low-input RNA-sequencing was conducted for the main endometrial compartments, luminal epithelium (LE), glandular epithelium (GE), blood vessels (BV), and stroma. Samples were isolated from endometria collected on Day 14 of pregnancy and the estrous cycle (each group n = 4) by laser capture microdissection. The expression of 12,000, 11,903, 11,094, and 11,933 genes was detectable in LE, GE, BV, and stroma, respectively. Differential expression analysis was performed between the pregnant and cyclic group for each cell type as well as for a corresponding dataset for complete endometrium tissue samples. The highest number of differentially expressed genes (DEGs) was found for LE (1410) compared to GE, BV, and stroma (800, 1216, and 384). For the complete tissue, 3262 DEGs were obtained. The DEGs were assigned to Gene Ontology (GO) terms to find overrepresented functional categories and pathways specific for the individual endometrial compartments. GO classification revealed that DEGs in LE were involved in 'biosynthetic processes', 'related to ion transport', and 'apoptotic processes', whereas 'cell migration', 'cell growth', 'signaling', and 'metabolic/biosynthetic processes' categories were enriched for GE. For blood vessels, categories such as 'focal adhesion', 'actin cytoskeleton', 'cell junction', 'cell differentiation and development' were found as overrepresented, while for stromal samples, most DEGs were assigned to 'extracellular matrix', 'gap junction', and 'ER to Golgi vesicles'.

CONCLUSIONS

The localization of differential gene expression to different endometrial cell types provided a significantly improved view on the regulation of biological processes involved in conceptus implantation, such as the control of uterine fluid secretion, trophoblast attachment, growth regulation by Wnt signaling and other signaling pathways, as well as the modulation of the maternal immune system.

Association of Polymorphisms in Candidate Genes with the Litter Size in Two Sheep Breeds

Hu sheep and Small-tailed Han sheep are the most widely raised and most famous maternal sheep breeds in China, which are known for precocious puberty, perennial oestrus and high fecundity (1-6 lambs each parity). Therefore, it is crucial to increase litter size of these two breeds for intensive sheep industry. The objective of this study was to identify potential genetic markers linked with sheep litter size located at ten genes. This study collected blood sample of 537 Hu sheep and 420 Small-tailed Han sheep with litter size of first parity. The average litter sizes in Hu sheep and Small-tailed Han sheep were 2.21 and 1.93. DNA-pooling sequencing method was used for detecting the potential single nucleotide polymorphisms (SNPs) in ten genes related to follicle development and female reproduction. SNPscan® was used for individually genotyping. As a result, a total of 78 putative SNPs in nine out of ten candidate genes (except NOG) were identified. In total, 50 SNPs were successfully genotyped in Hu sheep and Small-tailed Han sheep. After quality control, a total of 42 SNPs in Hu sheep and 44 SNPs in Small-tailed Han sheep were finally used for further analysis. Association analysis revealed that nine SNPs within six genes (KIT: g.70199073A>G, KITLG: g.124520653G>C, ADAMTS1: g.127753565T>C, ADAMTS1: g.127754640G>T, NCOA1: g.31928165C>T, NCOA1: g.32140565G>A, LIFR: g.35862868C>T, LIFR: g.35862947G>T and NGF: g.91795933T>C) were significantly associated with litter size in Hu sheep or Small-tailed Han sheep. A combined haplotypes analysis of the two loci (LIFR: g.35862868C>T and LIFR: g.35862947G>T) revealed that H2H3 (CTTT) combined haplotypes had the largest litter size than the rest combined haplotypes and more than those with either mutation alone in Small-tailed Han sheep. Taken together, our study suggests that nine significant SNPs in six genes can be served as useful genetic markers for MAS in sheep.

Pluripotency and X chromosome dynamics revealed in pig pre-gastrulating embryos by single cell analysis

High-resolution molecular programmes delineating the cellular foundations of mammalian embryogenesis have emerged recently. Similar analysis of human embryos is limited to pre-implantation stages, since early post-implantation embryos are largely inaccessible. Notwithstanding, we previously suggested conserved principles of pig and human early development. For further insight on pluripotent states and lineage delineation, we analysed pig embryos at single cell resolution. Here we show progressive segregation of inner cell mass and trophectoderm in early blastocysts, and of epiblast and hypoblast in late blastocysts. We show that following an emergent short naive pluripotent signature in early embryos, there is a protracted appearance of a primed signature in advanced embryonic stages. Dosage compensation with respect to the X-chromosome in females is attained via X-inactivation in late epiblasts. Detailed human-pig comparison is a basis towards comprehending early human development and a foundation for further studies of human pluripotent stem cell differentiation in pig interspecies chimeras.

Lineage segregation from conception to gastrulation has been mapped at the single cell level in mouse, human and monkey. Here, the authors provide a comprehensive analysis of porcine preimplantation development using single cell RNA-seq; mapping metabolic changes, X chromosome inactivation and signalling pathways.

Expression of leukaemia inhibitory factor at the conceptus?maternal interface during preimplantation development and in the endometrium during the oestrous cycle in the mare

Leukaemia inhibitory factor (LIF) plays a critical role in blastocyst development and implantation in several species. The present study investigated mRNA and protein expression for LIF, as well as the low-affinity LIF receptor (LIFR) and interleukin-6 signal transducer (IL6ST), in equine endometrium, trophoblast and histotroph during early pregnancy and in the endometrium during the oestrous cycle. Endometrial LIF mRNA expression was upregulated after Day 21 of pregnancy, whereas LIF immunoreactivity increased in the endometrium on Day 28. Expression of LIF mRNA in the yolk sac membrane increased from Day 21 of pregnancy, whereas LIF immunoreactivity increased from Day 28 in the trophoblast. LIFR and IL6ST mRNA was expressed in the endometrium during both the oestrous cycle and early pregnancy and, although LIFR and IL6ST protein were localised to the glandular epithelium during the cycle and first 14 days of pregnancy, from Day 21 they were located in the luminal epithelium. Trophoblast expression of LIFR and IL6ST increased as pregnancy proceeded. In conclusion, LIF expression increased at the conceptus-maternal interface during capsule attenuation. Because contemporaneous upregulation of both LIFR and IL6ST was also observed in the trophoblast, we propose that LIF plays an important role in the development of endometrial receptivity for trophoblast growth, apposition and adhesion in mares.

MicroRNAome of porcine conceptuses and trophoblasts: expression profile of micrornas and their potential to regulate genes crucial for establishment of pregnancy

Tightly coordinated, reciprocal embryo-maternal interactions affect gene expression during early pregnancy. Recently, microRNAs (miRNAs) have emerged as new players in the fine tuning of embryo development and implantation in mammals via posttranscriptional gene regulation mechanisms. Here, we integrated transcriptomic and computational approaches to profile miRNAs and miRNA synthesis and transport-related genes at different developmental stages of porcine conceptuses and trophoblast during early pregnancy in the pig. Using semiquantitative RT-PCR, we examined mRNA levels of 10 genes encoding proteins involved in miRNA synthesis and transport: DROSHA, DGCR8, XPO5, DICER1, TARBP2, TNRC6A, AGO1, AGO2, AGO3, and AGO4. Custom, multispecies microarrays were used to profile miRNAs. Prediction algorithms of miRNA-mRNA interactions allowed identification of target transcripts for the analyzed miRNAs. These included VEGF, LIF, PTGS2, and IL-6R, known to be crucial components of embryo-maternal interactions in the pig. Two selected miRNAs, miR-26a and miR-125b, were tested for the presence in the extracellular vesicles isolated from uterine luminal flushings during pregnancy. Results of in vitro study demonstrated that miRNAs, such as miR-125b, can regulate expression of genes crucial for embryo development and implantation in porcine endometrial luminal epithelial cells. For the first time, expression profiles of miRNAs and related genes in porcine conceptuses and trophoblast during maternal recognition of pregnancy and embryo implantation in the pig were described. Altogether, our results indicate potential roles of these small, noncoding RNAs in the early development of embryos and embryo-maternal cross-talk during early pregnancy in the pig.

Cytokines from the pig conceptus: roles in conceptus development in pigs

Establishment of pregnancy in pigs involves maintaining progesterone secretion from the corpora lutea in addition to regulating a sensitive interplay between the maternal immune system and attachment of the rapidly expanding trophoblast for nutrient absorption. The peri-implantation period of rapid trophoblastic elongation followed by attachment to the maternal uterine endometrium is critical for establishing a sufficient placental-uterine interface for subsequent nutrient transport for fetal survival to term, but is also marked by the required conceptus release of factors involved with stimulating uterine secretion of histotroph and modulation of the maternal immune system. Many endometrial genes activated by the conceptus secretory factors stimulate a tightly controlled proinflammatory response within the uterus. A number of the cytokines released by the elongating conceptuses stimulate inducible transcription factors such as nuclear factor kappa B (NFKB) potentially regulating the maternal uterine proinflammatory and immune response. This review will establish the current knowledge for the role of conceptus cytokine production and release in early development and establishment of pregnancy in the pig.

Global gene expression profiling of porcine endometria on Days 12 and 16 of the estrous cycle and pregnancy

The objective of the study was to investigate transcriptomic profile of pig endometrium on Days 12 and 16 of pregnancy in comparison with the respective days of the estrous cycle. Labeled complementary DNA was hybridized to Porcine Long Oligo microarray containing 13,297 oligonucleotide probes, which represented complementary DNA and expressed sequence tags. Statistical analysis revealed 110 differentially expressed genes (DEGs) on Day 12 of pregnancy and 179 DEGs on Day 16 of pregnancy. In silico analysis of gene function and functionality networks revealed links between genes implicated in cell death and survival, protein synthesis, lipid metabolism, cellular movement, tissue development, and cell-to-cell signaling. On Day 12 of pregnancy, estrogen, transforming growth factor (TGF) β1, and fibroblast growth factor (FGF) 2, and on Day 16 of pregnancy, epidermal growth factor (EGF), insulin, interleukin 11 (IL-11), and FGF family members were indicated as possible upstream regulators of several DEGs. Obtained results showed changes in global endometrial gene expression at the time of maternal recognition of pregnancy and embryo implantation. Additionally, these data revealed signaling molecules, which together with E2, may evoke molecular changes in the uterus, leading to successful pregnancy establishment.

Expression patterns of sirtuin genes in porcine preimplantation embryos and effects of sirtuin inhibitors on in vitro embryonic development after parthenogenetic activation and in vitro fertilization

We examined the expression patterns of porcine sirtuin 1 to 3 (Sirt1-3) genes in preimplantation embryos derived from parthenogenetic activation (PA), in vitro fertilization (IVF) and somatic cell nuclear transfer (SCNT). We also investigated the effects of sirtuin inhibitors (5 mM nicotinamide [NAM] and 100 μM sirtinol) on embryonic development of PA and IVF embryos under in vitro culture (IVC). The expression patterns of Sirt1-3 mRNA in preimplantation embryos of PA, IVF, and SCNT were significantly (P < 0.05) decreased from metaphase stage of oocyte to blastocyst stage. Especially, the expressions of Sirt1-3 in SCNT blastocysts were significantly (P < 0.05) lower and Sirt2 in PA blastocyst was significantly higher compared with the IVF blastocysts. Treatment with sirtuin inhibitors during IVC resulted in significantly (P < 0.05) decreased blastocyst formation and total cell number of blastocyst derived from PA (NAM: 29.4% and 29.6, sirtinol: 31.0% and 30.3, and control: 40.9% and 41.7, respectively) and IVF embryos (NAM: 10.4% and 30.9, sirtinol: 6.3% and 30.5, and control: 16.7% and 42.8, respectively). There was no significant difference in cleavage rate in both PA and IVF embryos. The early and expanded blastocyst formations at Day 7 were significantly lower in the sirtuin inhibitors-treated groups than the control. It was demonstrated that sirtuin inhibitor (NAM) influenced the percentage of blastocyst formation and total cell number of PA derived blastocyst when NAM was added during day 4 to 7 (22.1% and 32.4) or day 0 to 7 (23.1% and 31.6) of IVC compared with the control (41.8% and 41.5). No significant difference in cleavage rates appeared among the groups. The blastocysts derived from PA embryos treated with sirtuin inhibitors showed lower (P < 0.05) expressions of POU5F1 and Cdx2 genes. Also, Sirt2 mRNA expression was significantly decreased in sirtinol treated group and Sirt3 mRNA expression was also significantly decreased in both NAM and sirtinol treated groups compared with the control. In conclusion, these results suggest that sirtuins may have a physiological and important role in embryonic development of porcine preimplantation embryos by regulating essential gene expressions of developing embryos. These findings could have implications for understanding the role of sirtuins during embryo development and for improving SCNT and related techniques.

Regulation of expression and role of leukemia inhibitory factor and interleukin-6 in the uterus of early pregnant pigs

Cytokines, which are generally involved in the process of inflammation, may also play a critical role in conceptus implantation. We examined: (1) the expression profiles of leukemia inhibitory factor (LIF) and interleukin (IL)-6 mRNA and their protein content in the endometrium of cyclic and pregnant gilts on Days 10 to 18 after estrus; (2) the effect of conceptus-exposed medium on LIF and IL-6 synthesis in the endometrium; (3) the profiles of IL6R and LIFR mRNA expression in pig conceptuses collected on Days 10 to 18 of pregnancy; and (4) the effect of LIF and IL-6 on the attachment and proliferation of porcine trophoblast cells. The expression of LIF mRNA in the endometrium increased between Days 10 and 12 in both cyclic and pregnant gilts, and tended to be higher in Day 12 pregnant animals compared with nonpregnant ones. The LIF protein content in the uterine lumen peaked on Day 12 of pregnancy, and was higher than on Day 12 of the estrous cycle. Endometrial IL-6 mRNA expression was upregulated on Day 12 in pregnant gilts compared with nonpregnant animals. Moreover, a higher content of IL-6 protein was observed in pregnant than in cyclic gilts. The addition of conceptus-exposed medium resulted in up-regulation of LIF and IL6 mRNA expression, and increased IL-6 content in endometrial slices. In conceptuses, increased mRNA expression was detected on Days 10 to 14 for IL6R and on Day 14 for LIFR, when compared with other days studied. LIF and IL-6 stimulated the attachment and proliferation of trophoblast cells in vitro. In summary, LIF and IL-6 are important components of embryo-uterine interactions during early pregnancy in the pig, and may contribute to successful conceptus implantation.

Variability of mRNA abundance of leukemia inhibitory factor gene (LIF) in porcine ovary, oviduct and uterus tissues

The leukemia inhibitory factor (LIF) gene encodes a pleiotropic cytokine which is produced by the endometrium and plays an important role in implantation and early embryonic development. Because of its function, LIF gene is considered as a candidate gene for litter size in many mammalian species including pig. The aim of present study was to evaluate the expression of LIF gene in the porcine ovary, oviduct and two regions of uterus (corpus uteri, cornu uteri) in prepubertal and pubertal gilts. In order to precise estimation of LIF transcript abundance we evaluated the stability of expression for several candidate housekeeping genes in investigated tissues across different breeds and different stage of oestrus cycle. The geNorm analysis indicated that the most stable reference genes across analyzed tissues were: OAZ1 and RPL27. The analysis conducted separately for each tissue confirmed that the most stable gene was OAZ1 in all tissues expect oviduct (the most stable was RPL27 gene). In prepubertal pigs, the highest level of the LIF expression was obtained in both regions of uterus compare to ovary and oviduct tissues (P < 0.01). A similar trend in LIF expression pattern was observed in follicular phase-the significantly highest transcript level was obtained in cornu uteri, it was about ninefold higher than in ovary (P < 0.05). In luteal stage the highest expression was in corpus uteri. In pig, the high expression in luteal phases suggested that, LIF may be mainly secreted in respond to the increased of progesterone concentration and it can be connected with the preparation of the uterus for implantation.

Porcine granulocyte-macrophage colony-stimulating factor improves the in vitro development of cloned porcine embryos

We examined the effects of porcine granulocyte-macrophage colony-stimulating factor (pGM-CSF) on the in vitro development of porcine embryos produced by somatic cell nuclear transfer (SCNT) for the first time. We evaluated the effects of pGM-CSF on SCNT-derived blastocyst formation and investigated gene expression. A total of 522 cloned embryos in 6 replicates were treated with 10 ng/ml pGM-CSF during in vitro culture (IVC). This treatment significantly (P<0.05) increased blastocyst formation and total cell number in blastocysts compared with the control (12.3% and 41.4 vs. 9.0% and 34.7, respectively). However, there was no effect on cleavage rate. The numbers of cells in the inner cell mass and trophectoderm were significantly higher in the pGM-CSF treatment group (6.0 and 43.0, respectively) compared with the control (4.4 and 31.9, respectively). Treatment with 10 ng/ml pGM-CSF significantly increased POU5F1 and Cdx2 mRNA expression in blastocysts. In addition, Bcl-2, Dnmt1 and proliferating cell nuclear antigen (PCNA) mRNA expression were upregulated in blastocysts in the pGM-CSF supplemented group compared with the control. These results suggest that pGM-CSF improves the quality and developmental viability of porcine SCNT embryos by regulating transcription factor expression.

Embryo-maternal communication: signalling before and during placentation in cattle and pig

Communication during early pregnancy is essential for successful reproduction. In this review we address the beginning of the communication between mother and developing embryo; including morphological and transcriptional changes in the endometrium as well as epigenetic regulation mechanisms directing the placentation. An increasing knowledge of the embryo-maternal communication might not only help to improve the fertility of our farm animals but also our understanding of human health and reproduction.

Interaction of the conceptus and endometrium to establish pregnancy in mammals: role of interleukin 1β

Implantation and the establishment of pregnancy in mammals involves an intricate interplay of hormones, cytokines, growth factors, proteins, lipids, ions and the extracellular matrix between the uterine epithelium, stroma, immune cells and the conceptus trophectoderm. The divergent nature of implantation in the mouse, human and pig provides not only an interesting contrast in the establishment of pregnancy and early embryonic development but also intriguing similarities with regard to early endometrial-conceptus signaling. An interesting pro-inflammatory cytokine expressed in a number of mammalian species during the period of implantation is interleukin-1β (IL1B). The presence of IL1B might be involved with immunotolerance at the maternal-placental interface and has been proposed as one of the mediators in placental viviparity. The production of IL1B and other proinflammatory cytokines might play a role in establishing pregnancy through modulation of the nuclear factor kappa-B (NFKB) system in a number of species. A model for the regulation of cellular progesterone receptor expression and NFKB activation for endometrial receptivity and conceptus attachment is continuing to evolve and is discussed in the present review.

Effects of porcine granulocyte-macrophage colony-stimulating factor on porcine in vitro-fertilized embryos

This study investigated the effects of porcine granulocyte-macrophage colony-stimulating factor (pGM-CSF) on the developmental potential of porcine in vitro-fertilized (IVF) embryos in chemically and semidefined (with BSA) medium. In experiment 1, zygotes were treated with different concentrations of pGM-CSF (0, 2, 10, 100 ng/mL). The results indicated that 10 ng/mL pGM-CSF significantly (P < 0.05) increased blastocyst development and total cell number (15.1% and 53.5, respectively) compared with the control (6.1%, and 38.8, respectively). Comparing blastocyst formation, early and expanded blastocyst formation was significantly higher in the 10 ng/mL-pGM-CSF group than in the control on Days 6 and 7 of the culture period. However, there was no significant difference in cleavage rate. Experiment 2 demonstrated that pGM-CSF influenced the percentage of blastocyst formation and total cell number when pGM-CSF was added during Days 4 to 7 (14.6% and 53.9, respectively) or Days 0 to 7 (15.2% and 54.0, respectively) compared with the control (7.8% and 43.1, respectively) and compared with Days 0 to 3 (8.7% and 42.5, respectively). Similarly, early blastocyst formation rates were significantly higher at Days 4 to 7 than in the control, and expanded blastocyst formation was significantly higher at Days 4 to 7 or Days 0 to 7. No significant difference in cleavage rates appeared among the groups. In experiment 3, in the presence of BSA, pGM-CSF also increased the percentage of embryos that developed to the blastocyst stage and the total cell number (20.3% and 59.8, respectively) compared with the control (14.9% and 51.4, respectively), whereas there was no significant difference in cleavage rate. Experiment 4 found that the total cell number and the number of cells in the inner cell mass (ICM) were significantly increased compared with the control when zygotes were cultured in either porcine zygotic medium (PZM)-3 or PZM-4 supplemented with 10 ng/mL pGM-CSF. The number of trophectoderm (TE) cells was significantly higher in PZM-3 medium supplemented with pGM-CSF than in the control, and the number tended to increase (P = 0.058) in PZM-4 medium supplemented with pGM-CSF. The ratio of inner cell mass to trophectoderm cells was significantly higher in PZM-4 supplemented with 10 ng/mL pGM-CSF, but not in PZM-3. In experiment 5, it was found that the male pronuclear formation rate, monospermic penetration and sperm/oocyte were 95.4%, 37.2%, and 2.4, respectively. Together, these results suggest that pGM-CSF may have a physiological role in promoting the development of porcine preimplantation embryos and regulating cell viability and that addition of pGM-CSF to IVC medium at Days 4 to 7 or 0 to 7 improves the developmental potential of porcine IVF embryos.

Embryo implantation is blocked by intraperitoneal injection with anti-LIF antibody in mice

Leukemia inhibitory factor (LIF) is essential for embryo implantation in mice and plays an important role in other mammals including humans. Intraperitoneal (i.p.) injections with anti-LIF antibody (7.5 µg/g body weight, 3 times) between D3 (D1 = day of vaginal plug detection) and D4 effectively blocked embryo implantation; complete inhibition was achieved in C57BL/6J mice, and implantation was dramatically reduced in ICR mice (reduced to 27%). Normal rabbit IgG used as the control did not disturb embryo implantation. Anti-LIF antibody was localized not only in the stroma, but also in the luminal epithelium and the glandular lumen after i.p. injections. Growth-arrested blastocysts were recovered from the uterus without any implantation sites in both strains. Blastocysts made contact with the LE on the antimesometrial side; however, uterine stromal cells did not undergo secondary decidual reaction, and the uterine lumen was open, even at D7. Several regions of decidualization in ICR mice treated with anti-LIF antibody were smaller than those of the control, and development of blastocysts was delayed. The expression of LIF-regulated genes, such as immune-responsive gene-1 and insulin-like growth factor binding protein-3, was significantly decreased in C57BL/6J mice treated with anti-LIF antibody compared with the control, but not in ICR mice. The present study demonstrated that simple ip injections of an antibody are sufficient to block one of the important factors involved in embryo implantation in mice, and this method should also be easily applicable to the investigation of other factors involved in implantation.

Endometrial and conceptus expression of HoxA10, transforming growth factor beta1, leukemia inhibitory factor, and prostaglandin H synthase-2 in early pregnant pigs with gonadotropin-induced estrus

This study was conducted to evaluate the effect of estrus induction with gonadotropins on endometrial and conceptus expression of HoxA10, transforming growth factor (TGF) beta1, leukemia inhibitory factor (LIF), and prostaglandin H synthase-2 (PGHS-2) during early pregnancy in pigs. Twenty-four prepubertal gilts received 750 IU of pregnant mare serum gonadotropin (PMSG) and 500 IU of human chorionic gonadotropin (hCG) 72h later. Gilts in the control group (n=23) were observed daily for estrus behavior. Endometrial tissue samples, conceptuses, blood serum, and uterine luminal flushings (ULFs) were collected on days 10, 11, 12, and 15 after insemination. There was no effect of estrus induction on estradiol content in ULFs, or on ovulation and fertilization rates in studied gilts. However, the content of progesterone in the blood serum was greater in naturally ovulated gilts in comparison to gonadotropin-treated animals on day 12 of pregnancy (P<0.05). HoxA10 expression was up-regulated in the endometrium of pregnant gilts, with natural ovulation on days 12 (P<0.05) and 15 (P<0.001) in comparison to days 10 and 11. When compared to control gilts, administration of PMSG/hCG resulted in decreased expression of endometrial HoxA10, TGFbeta, LIF, and PGHS-2 on day 12 of pregnancy (P<0.05). Conceptus expression of studied factors was not affected by gonadotropin treatment. Overall, these results suggest improper endometrial preparation for implantation in prepubertal gilts induced to ovulate with PMSG/hCG.

Activation of the transcription factor, nuclear factor kappa-B, during the estrous cycle and early pregnancy in the pig

Establishment and maintenance of pregnancy in the pig involves intricate communication between the developing conceptuses and the maternal endometrium. This process occurs during trophoblast elongation which is spaciotemporally associated with conceptus synthesis and release of IL1B concomitant with pregnancy-specific endometrial up-regulation of IL-1 receptors, providing the potential for activation of the transcription factor, NFKB. The objective of the current investigation was to determine changes in expression and cellular localization of NFKB and associated factors during the estrous cycle and early pregnancy in the pig. In situ hybridization was used to localize changes in PGR, ESR1, and TNFRSF11A during the peri-implantation period. Quantitative RT-PCR was utilized to demonstrate gene expression changes for NFKB1, RELA, TNFRSF11A, TLR4, NFKBIA and NFKBIB. Transcription factor ELISA demonstrated an overall increase in RELA during the peri-implantation period in both cyclic and pregnant gilts. While the presence of TNFSF11A and TLR4 were both detected, TLR4 expression changes were temporally associated with NFKB expression and activation. Collectively, these data demonstrate that NFKB activation may occur during the period of uterine receptivity in both the cyclic and pregnant endometrium.

Effect of polymorphism in the leukemia inhibitory factor gene on litter size in Large White pigs

DNA polymorphism of the porcine leukemia inhibitory factory (LIF) was investigated and used to study the effects on litter size in Large White pigs. A total of 2,167 litter records from 420 sows genotyped at two SNP loci (LIF1 and LIF2) within LIF gene were analyzed to determine whether LIF influenced total number born (TNB) and number born alive (NBA). The results indicated that B allele at LIF1 locus and A allele at LIF2 locus seem to have advantageous effects on litter size. However, the combined analyzed results demonstrated that genotype AAAA, ABBB, and BBBB are better than genotype AAAB, AABB, and ABAB for TNB and NBA in either third to eighth parity or all parities. In all parities, the sows with AAAA genotype had an advantage of 1.76 piglets (P < 0.001) for TNB and 1.44 piglets (P < 0.01) for NBA per litter over the AAAB sows, respectively. The results in this study demonstrated that LIF gene was significantly associated with litter size in pigs.

Effect of polymorphisms in the genes for LIF and RBP4 on litter size in two German pig lines

The association of two diallelic polymorphisms in the porcine genes for leukaemia inhibitory factor (LIF) and retinol-binding protein 4 (RBP4) with number of piglets born alive (NBA) in two German pig lines was studied. The investigated single nucleotide polymorphism (SNP) in the porcine LIF gene has been located in the 3'-untranslated region of its third exon, whereas the SNP in the RBP4 gene genotyped in this study is intronic. At the LIF locus the allele frequencies were 0.613 for the A allele and 0.387 for the B allele in German Landrace (GL) and 0.276 for A and 0.724 for B in German Large White (GW). At the RBP4 locus, the allele frequencies were 0.586 for the A allele and 0.414 for the B allele in GL and 0.733 for A and 0.267 for B in GW. There was a significant additive effect of the LIF B allele on NBA in GW over all parities (p <or= 0.05) and a significant positive dominance effect of 0.69 +/- 0.22 (p = 0.002) was observed for first parity on NBA in GL. For RBP4, no association of genotypes and NBA was detected in GW but a significant additive effect of the A allele of 0.24 +/- 0.11 (p = 0.027) and a significant dominance effect of 0.31 +/- 0.13 (p = 0.020) were found in GL over all parities and confirmed through the evaluations by parity.

Evidence of a new leukemia inhibitory factor-associated genetic marker for litter size in a synthetic pig line

The association of a diallelic polymorphism in the leukemia inhibitory factor (LIF) gene with reproductive, growth, and carcass traits was studied in a German synthetic pig line. The diallelic SNP has been located in the 3'-untranslated region of the third exon of the porcine LIF gene. Information on 955 litter records from 273 genotyped sows was used in the analyses with respect to the number of piglets born alive. To identify possible pleiotropic marker effects, the growth and carcass traits ADG and backfat thickness were tested for associations with the SNP within the LIF gene in this population. At the LIF locus, the allele frequencies were 0.27 for the A allele and 0.73 for the B allele. There was an indication of an additive effect on the number of piglets born alive, and a significant dominance effect of the B allele was observed for first, second, and third to 10th parities (P = 0.044). The dominance effect for the first parity amounted to -0.73 +/- 0.36 (P = 0.047). No associations were detected between the marker alleles and the growth and carcass traits.

Pleiotropy and Redundancy of STAT Proteins in Early Pregnancy

Signal transducers and activators of transcription (STATs) are a group of proteins involved in signal transduction from numerous bioactive substances. Hormones and cytokines such as leukaemia inhibitory factor, interferon-tau and prolactin, which play key roles during early pregnancy, activate the Janus kinase (JAK)/STAT signalling pathway. The STATs are thus involved in the regulation of implantation, establishing uterine receptivity and regulation of the maternal immune response. It seems that STATs can orchestrate signals from hormones and cytokines in different cell types and may therefore generate numerous biological effects, despite the relatively small number of receptors activating the JAK/STAT pathway. This review summarizes the participation of STATs in the main processes of early pregnancy, especially regarding their pleiotropy and redundancy.

Leukaemia inhibitory factor enhances sheep fertilization in vitro via an influence on the oocyte

LIF is twice transiently expressed in the mouse uterus, first at the time of ovulation and again just prior to implantation, and studies have demonstrated a beneficial influence of this cytokine on embryo development in several species. We have investigated the effect of LIF on gametes in vitro, on the hypothesis that the ovulatory peak of LIF can exert an influence on gametes present within the oviduct. We also investigated the effect of LIF on in vitro fertilization and embryo development, in oocytes from adult sheep and from prepubertal lambs that lack the preovulatory hormone surge and that are unable to sustain early embryonic development. A higher rate of pronuclear-stage embryos derived from both, adult and prepubertal female, was obtained when in vitro fertilization was performed in the presence of LIF, and there was an improved cleavage of parthenogenetic embryos when incubated with LIF immediately following activation. In contrast, LIF was found to have no influence on the viability of ram semen. In vitro fertilized two-cell stage embryos from adult sheep and prepubertal lambs, cultured in defined medium enriched with LIF, both reached the blastocyst stage at similar rates to control embryos. However, LIF exerted a positive influence on the quality of the blastocysts as revealed by significantly higher number of ICM cells and total number of cells. Together, these data demonstrate that LIF exerts a beneficial effect on sheep oocytes and embryos in vitro, but only at stages concomitant with steroid hormones surges.

Genetic approaches to the improvement of fertility traits in the pig

One of the major determinants for litter size in pigs is prenatal mortality. It occurs most frequently during the first few weeks of gestation and can be attributed to abnormalities in developmental processes during embryogenesis including trophoblastic elongation and blastocyst implantation. Improvement of litter size has been attempted by means of phenotypic selection. However, another promising approach in pursuit of this aim has been the use of genotypic information. Reproductive traits in general are well-suited for application of marker-assisted selection (MAS). The possibility of exerting selection criteria at the molecular level shortens the generation interval as the selection decision can take place early in the life of an animal. Moreover, in consideration of the sex-limited nature of reproductive traits, genotypic information allows for selection in the gender in which the trait cannot be directly observed. Accordingly, there has been considerable interest in mapping and identifying genes involved in the regulation of reproductive traits and in elucidating their expression patterns. This review offers a comprehensive, if not exhaustive, account of the efforts being made and the approaches currently used in this field. One approach has been to choose candidate genes a priori because of the physiological importance of the proteins they encode and their role in the reproduction of other mammals. The usefulness of candidate genes is then examined by association studies between genetic polymorphisms identified in the respective candidate genes and the phenotypic reproductive traits. The other approach discussed uses pre-existing or designed families for linkage analyses in order to map the location of quantitative trait loci (QTL) for the reproductive trait of interest. The results reported were not consistent among different studies but the QTL regions detected may be useful for identification of positional candidate genes in further molecular genetic studies. However, a better understanding of porcine reproduction requires that these functional genomic approaches are merged and integrated with detailed analyses of the proteome to establish linkages between predisposition and physiology.

Characterization of the interleukin-1beta system during porcine trophoblastic elongation and early placental attachment

Conceptus-uterine communication is established during trophoblastic elongation when the conceptus synthesizes and releases estrogen, the maternal recognition signal in the pig. Interleukin-1beta (IL-1beta) is a differentially expressed gene during rapid trophoblastic elongation in the pig. The current investigation determined conceptus and endometrial changes in gene expression for IL-1beta, IL-1 receptor antagonist (IL-1Rant), IL-1 receptor type 1 (IL-1RT1), and IL-1 receptor accessory protein (IL-1RAP) in developing peri- and postimplantation conceptuses as well as uterine endometrium collected from cyclic and pregnant gilts. Conceptus IL-1beta gene expression was enhanced during the period of rapid trophoblastic elongation compared with earlier spherical conceptuses, followed by a dramatic decrease in elongated Day 15 conceptuses. IL-1RT1 and IL-1RAP gene expression was greater in Day 12 and 15 filamentous conceptuses compared with earlier morphologies while IL-1Rant gene expression was unchanged by conceptus development. The uterine lumenal content of IL-1beta increased during the process of trophoblastic elongation on Day 12. Uterine IL-1beta content declined on Day 15, reaching a nadir by Day 18 of pregnancy. IL-1beta gene expression in porcine conceptuses was temporally associated with an increase in endometrial IL-1RT1 and IL-1RAP gene expression in pregnant gilts. Endometrial IL-1beta and IL-1Rant gene expression were lowest during Days 10-15 of the estrous cycle and pregnancy. The temporal expression of IL-1beta during conceptus development and the initiation of conceptus-uterine communication suggests conceptus IL-1beta synthesis plays an important role in porcine conceptus elongation and the establishment of pregnancy in the pig.

Dual control of LIF expression and LIF receptor function regulate Stat3 activation at the onset of uterine receptivity and embryo implantation

Leukemia inhibitory factor (LIF) expression in the uterus is essential for embryo implantation in mice. Here we describe the spatial and temporal regulation of LIF signaling in vivo by using tissues isolated from uteri on different days over the implantation period. During this time, LIF receptors are expressed predominantly in the luminal epithelium (LE) of the uterus. Isolated epithelium responds to LIF by phosphorylation and nuclear translocation of signal transducer and activator of transcription (Stat) 3, but not by an increase in mitogen-activated protein kinase levels. The related cytokines Il-6, ciliary neurotrophic factor, as well as epidermal growth factor, do not activate Stat3, although epidermal growth factor stimulates mitogen-activated protein kinase. In vivo Stat3 activation is induced by LIF alone, resulting in the localization of Stat3 specifically to the nuclei of the LE coinciding with the onset of uterine receptivity. The responsiveness of the LE to LIF is regulated temporally, with Stat activation being restricted to day 4 of pregnancy despite the presence of constant levels of LIF receptor throughout the preimplantation period. Uterine receptivity is therefore under dual control and is regulated by both the onset of LIF expression in the endometrial glands and the release from inhibition of receptor function in the LE.

Preimplantation development of the mammalian embryo and its regulation by growth factors

Preimplantation development in mammals involves both the development of the embryo and the preparation of the uterus in anticipation of blastocysts implantation. Preparation of the uterus for implantation is primarily under the control of the ovarian sex steroids, estrogen and progesterone. Increasing evidence is revealing that their effects on cell proliferation and differentiation in the uterus are medicated by locally produced growth factors and cytokines. In contrast, preimplantation development of the embryo to the blastocyst stage appears to be independent of exogenous growth factors. Implantation, the point at which the blastocyst forms a more intimate association with the maternal tissues, is regulated by the uterine expression of leukemia inhibitory factor (LIF). LIF is required both to promote embryo attachment and for decidualization of the uterus. In the absence of LIF, neither of these events occur. Uterine expression of LIF at the time of implantation has been described in many species, suggesting that LIF may be of general significance in regulating embryo implantation in mammals.

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.

Pregnancy-dependent expression of leukaemia inhibitory factor (LIF), LIF receptor-beta and interleukin-6 (IL-6) messenger ribonucleic acids in the porcine female reproductive tract

Leukaemia inhibitory factor (LIF) and interleukin-6 (IL-6) are candidate embryo-maternal signalling molecules which are present within the uterine luminal micro-environment. We examined the relative expression of the mRNAs encoding LIF and IL-6, as well as the LIF-binding subunit (LIFR-beta) of the LIF receptor and, as a potential downstream cytokine-responsive gene, beta(2)-microglobulin (beta(2)m), in porcine peri-implantation conceptuses, and in placenta and endometrium during early and mid-pregnancy. Peri-implantation spherical and filamentous conceptuses expressed LIFR-beta and beta(2)m mRNAs with no LIF mRNA present. Rapid development in days 11/12 spherical conceptuses to the filamentous stage was accompanied by transiently increased IL-6 gene expression. The corresponding endometrium, in contrast, expressed LIF in addition to these other mRNAs. LIFR-beta, IL-6 and beta(2)m, but not LIF mRNAs, were expressed in the Jag-1 cell line, an in vitro model for porcine day 14 trophoblast. The greatest steady-state amounts of LIF, LIFR-beta and IL-6 mRNAs in both the endometrium and placenta were evident at the post-implantation stages (days 30 and 60>day 18 of pregnancy). Treatment of porcine endometrial explants with human recombinant (hr)LIF or hrIL-6 resulted in no change in, or diminished, the presence of endometrial beta(2)m mRNA, respectively. Addition of LIF to peri-implantation conceptus explant cultures, in contrast, induced beta(2)m mRNA synthesis. These results highlight the potential importance of both the endometrium and placenta as sources, as well as targets, of these cytokines throughout pregnancy. Cytokine modulation of beta(2)m, a known in vitro mitogen, may constitute one mechanism for local control of trophoblast and endometrial proliferation.

Interleukin-6 and tumor necrosis factor-alpha concentrations in the intrauterine cavity of postmenopausal women using an intrauterine delivery system releasing progesterone. A possible mechanism of action of the intrauterine device

Intrauterine devices (IUD) provide effective contraception. The current study evaluates the concentration of interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-alpha) in the intrauterine fluid of postmenopausal women using an intrauterine delivery system releasing progesterone (IDS-P). Intrauterine fluid was obtained by lavage, and IL-6 and TNF-alpha were analyzed using an enzyme-linked immunosorbent assay (ELISA). Statistical analysis was performed with a one-way analysis of variance (ANOVA). Intrauterine fluid IL-6 levels were 33.6 vs 6.09 pg/sample IDS-P vs no IDS-P (p = 0.0301). Intrauterine TNF-alpha levels for women using the IDS-P were higher than in nonusers, but the differences did not reach statistical significance. IL-6 and TNF-alpha levels were increased in the intrauterine cavity of postmenopausal women with an IDS-P. These data suggest that secreted cytokines could be a potential mechanism of IUD contraceptive efficacy.

Changes in uterine expression of leukemia inhibitory factor during pregnancy in the Western spotted skunk

Mutation of the leukemia inhibitory factor (LIF) gene results in reproductive failure in LIF -/- mice due to an inability to implant their blastocysts. This condition is reversed by infusion of LIF or by transferral of embryos to pseudopregnant, wild-type mice. This led us to hypothesize that embryonic diapause in the spotted skunk is due to insufficient uterine expression of LIF whereas resumption of development and implantation are associated with increased LIF expression. We also investigated the hormonal control of LIF expression. Uterine concentrations of LIF mRNA were determined by quantitative reverse transcription-polymerase chain reaction. Changes in cell-specific localization of LIF mRNA and protein were determined by in situ hybridization and immunocytochemistry. LIF mRNA was detected but was not abundant during embryonic diapause; it then increased when blastocysts resumed development and remained elevated prior to implantation. LIF mRNA and protein could not be localized in the uterus during embryonic diapause but were quite apparent in luminal and glandular epithelium during blastocyst activation. Prolactin, progesterone, and estradiol failed to increase uterine concentrations of LIF mRNA above those in ovariectomized controls. These data are consistent with the initial hypothesis and suggest that LIF may somehow be involved in preparing the uterus for implantation in the spotted skunk.

Paracrine inducers of uterine endometrial spermidine/spermine N1-acetyltransferase gene expression during early pregnancy in the pig

The endogenous factors that underlie the transient induction of the gene encoding spermidine/spermine N1-acetyltransferase (SSAT), the rate-limiting enzyme in cellular polyamine catabolism, in pig uterine endometrium during periimplantation are not known. The present study examined a number of peptide growth factors and regulatory molecules that are present within the uterine environment at early pregnancy, coincident with maximal SSAT gene expression, for their ability to manifest endogenous SSAT gene-inducing activity. Basal SSAT expression in luminal epithelial cells was higher (p < 0. 01) than that for glandular epithelial (GE) or stromal (ST) cells. Recombinant human insulin-like growth factor-I (IGF-I; 50 ng/ml) had no effect on steady-state SSAT mRNA levels, but it increased mitogenesis in all three cell types. In contrast, IGF-I caused a marked induction (p < 0.01) of SSAT mRNA levels in the human endometrial carcinoma cell line Hec-1-A. Uterine explants incubated with interleukin-6, transforming growth factor alpha, epidermal growth factor (each at 1, 10, and 100 ng/ml), retinoic acid and retinol (each at 0.01, 0.1, and 1 microM), and estradiol-17beta (10 nM) had SSAT mRNA levels similar to controls. By contrast, leukemia inhibitory factor (LIF; at 10 and 100 ng/ml) caused a modest, but significant (p < 0.05), increase in SSAT mRNA levels over those of untreated explants. This effect of LIF, however, did not approach the level of induction observed in GE or ST cells after addition of medium conditioned by Day 12 or 17 porcine conceptuses and in endometrial explants supplemented with medium conditioned by Day 21 porcine conceptuses or a continuous cell line (Jag-1) derived from Day 14 porcine trophoblast. We suggest that transient induction of endometrial SSAT gene expression at implantation is mediated by the functional interactions of specific conceptus-derived regulatory factors, distinct from estrogen, with endometrial-derived factor(s) such as LIF. These complex interactions are probably requisite for the transient, yet dramatic, induction of SSAT gene expression and may be critical for successful implantation.

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.