Progesterone and Placental Hormone Actions on the Uterus: Insights from Domestic Animals1

Effect of steroids on HOXA10 mRNA and protein expression and prostaglandin production in the porcine endometrium

The homeobox A (HOXA) family of genes is responsible for segmental development of the female reproductive tract during embryogenesis. However, HOXA10 has been shown to be essential not only for uterus development, but also for implantation. Persistent expression and steroid-dependent regulation of this gene has been demonstrated in adult human, primate, murine and canine uteri. Moreover, HOXA10-dependent expression of prostaglandin H synthase-2 (PGHS-2), a key enzyme in prostaglandin production, has been previously detected. The role of the HOXA10 gene in the porcine uterus is not well established. Therefore, the present studies were undertaken to 1) examine the effect of E(2) and P(4) on HOXA10 mRNA and protein content in the endometrium collected on day 9 of the estrous cycle and 2) determine the PGHS-2 protein expression and PGE(2) and PGF(2α) secretion from endometrial tissue in response to steroid treatment. Endometrial explants collected from mature gilts on day 9 of the estrous cycle were incubated with E(2) (1-100 nM), P(4) (10-1000 nM) or E(2) (10 nM) and P(4) (100 nM) for 24 h. E(2) alone or E(2) in the presence of P(4) increased HOXA10 mRNA expression in the endometrium (P<0.05). The HOXA10 protein level was upregulated in response to E(2), P(4) and both steroids administered simultaneously (P<0.05). Moreover, E(2) and P(4) stimulated PGHS-2 protein expression in cultured endometrial explants. PGE(2), but not PGF(2α), secretion increased in the presence of E(2) (P<0.05). However, the release of both prostaglandins was decreased after treatment of endometrial explants with the highest dose of P(4) (P<0.01). These results demonstrate that E(2) and P(4) are important regulators of HOXA10 gene expression in the adult porcine endometrium during the mid-luteal phase of the estrous cycle. Additionally, the similar profiles of endometrial HOXA10 and PGHS-2 expression in the presence of E(2) and P(4) indicate that both genes are simultaneously regulated by steroids in the porcine uterus.

Placental development during early pregnancy in sheep: vascular growth and expression of angiogenic factors in maternal placenta

Placental vascular development (angiogenesis) is critical for placental function and thus for normal embryonic/fetal growth and development. Specific environmental factors or use of assisted reproductive techniques may result in poor placental angiogenesis, which may contribute to embryonic losses and/or fetal growth retardation. Uterine tissues were collected on days 14, 16, 18, 20, 22, 24, 26, 28, and 30 after mating and on day 10 after estrus (nonpregnant controls) to determine vascular development and expression of several factors involved in the regulation of angiogenesis in the endometrium. Compared with controls, several measurements of endometrial vascularity increased (P<0.001) including vascular labeling index (LI; proportion of proliferating cells), the tissue area occupied by capillaries, area per capillary (capillary size), total capillary circumference per unit of tissue area, and expression of factor VIII (marker of endothelial cells), but capillary number decreased (P<0.001). Compared with controls, mRNA for placental growth factor, vascular endothelial growth factor receptors, angiopoietins (ANGPT) 1 and 2, ANGPT receptorTEK, endothelial nitric oxide synthase, and hypoxia-inducible factor 1α increased (P<0.05) during early pregnancy. Vascular LI was positively correlated (P<0.05) with several measurements of vascularity and with mRNA expression of angiogenic factors. These data indicate that endometrial angiogenesis, manifested by increased vascularity and increased expression of several factors involved in the regulation of angiogenesis, is initiated very early in pregnancy. This more complete description of early placental angiogenesis may provide the foundation for determining whether placental vascular development is altered in compromised pregnancies.

Expression of extracellular matrix metalloproteinase inducer (EMMPRIN) and its related extracellular matrix degrading enzymes in the endometrium during estrous cycle and early gestation in cattle

BACKGROUND

Extracellular matrix metalloproteinase inducer (EMMPRIN) regulates several biological functions involving the modulation of cell behaviors via cell-cell and cell-matrix interactions. According to its diverse functions, we hypothesized that EMMPRIN may play an important role in endometrial remodeling and establishment of pregnancy in cow.

METHODS

In this study, endometrial tissues from the cyclic cows during before ovulation, after ovulation and middle of estrous cycle; and pregnant endometrial tissues from Day 19 to 35 of gestation have been used. Expression of mRNA was analyzed by RT-PCR, qPCR and in situ hybridization whereas protein expression by immunohistochemistry and western blot analysis.

RESULTS

EMMPRIN mRNA was expressed in both cyclic and pregnant endometrium and significantly higher in the endometrium at Day 35 of gestation than the cyclic endometrium. In Western blot analysis, an approximately 65 kDa band was detected in the endometrium, and approximately 51 kDa in the cultured bovine epithelial cells and BT-1 cells, respectively. Both in situ hybridization and immunohistochemistry data showed that EMMPRIN was primarily expressed in luminal and glandular epithelium with strong staining on Day 19 conceptus. At Day 19 of gestation, expression of EMMPRIN mRNA on luminal epithelium was decreased than that observed at middle of estrous cycle, however, on Day 30 of gestation, slightly increased expression was found at the site of placentation. Expression of matrix metalloproteinase-2 (MMP-2) and MMP-14 mRNA were mainly detected in stroma and their expression also decreased at Day 19 of gestation however it was also expressed at the site of placentation at Day 30 of gestation as observed for EMMPRIN. Expression of MMP-1 or -9 mRNA was very low and was below the detection limit in the cyclic and pregnant endometrium.

CONCLUSION

EMMPRIN from the luminal epithelium may regulate the expression of stromal MMP-2 and -14 suggesting its crucial role in adhesion and fusion of embryo to luminal epithelium by directly itself through physiological tissues remodeling and developmental process, and/or stimulating MMPs to compensate endometrial functions.

Uterine progesterone receptor and leukaemia inhibitory factor mRNA expression in canine pregnancy

The study investigated the expression of genes for progesterone receptor (PR) and for the cytokine leukaemia inhibitory factor (LIF) in the uterine tube and uterine horn tissues from pregnant and non-pregnant bitches. The aim was to study whether a relation existed between the likely biological effectiveness of progesterone (P(4)) and the change in the uterine expression of LIF mRNA during pregnancy, as has been described in primates. For this purpose, 20 pregnant bitches were ovariohysterectomized after being allotted to three groups according to gestational age (pre-implantation: days 10 to 12, n = 7; peri-implantation: days 18 to 25, n = 7; post-placentation: days 28 to 45, n = 7). Tissue samples were obtained from the uterine tubes, one uterine horn (including placentation sites and interplacental sites in bitches that had already implanted) and the corpus uteri, stored at -80 degrees C, and then analysed by qualitative and quantitative PCR for PR and LIF mRNA expression. From the pre-implantation to the placentation stage, a decrease in the relative expression of PR mRNA in uterine tissue was obvious and significant when expressed relative to beta-actin (11.2 +/- 6.8 vs 2.7 +/- 1.9; p < 0.05). However, over the same period, the relative expression of LIF mRNA increased (10.1 +/- 16.1 vs 50.0 +/- 32.3; p < 0.05). In addition, PR mRNA went from being detectable to no longer detectable in the uterine tube, and no longer detectable in interplacental-site uterine tissue. We conclude that LIF is important for the establishment of canine pregnancy; that decreased uterine PR mRNA expression may contribute to the increase in uterine LIF mRNA; and, that the ability of the embryo to preserve PR mRNA expression at implantation and placentation sites while expression is lost in the remainder of the uterus represent an effect important to the establishment and maintenance of pregnancy. We additionally propose that canine embryo secretory proteins have a regulatory effect on both PR and LIF before as well as at and after implantation.

Progesterone and interferon tau-regulated genes in the ovine uterine endometrium: identification of periostin as a potential mediator of conceptus elongation

During early pregnancy in ruminants, progesterone (P4) and interferon tau (IFNT) act on the endometrium to regulate genes hypothesized to be important for conceptus development and implantation. The present study was conducted to verify several candidate genes (actin α-2, smooth muscle, aorta (ACTA2), collagen, type III, α-1 (COL3A1), periostin (POSTN), secreted protein acidic cysteine-rich (SPARC), S100 calcium-binding protein A2 (S100A2),STAT5Aand transgelin (TAGLN)) regulated by pregnancy, P4, and/or IFNT in the endometrium determined using a custom ovine cDNA array.S100A2mRNA was detected primarily in endometrial epithelia and conceptuses.S100A2mRNA increased in endometrial epithelia from days 10 to 16 in cyclic ewes and from days 10 to 14 in pregnant ewes and declined thereafter. The abundance ofS100A2mRNA was less in endometrial luminal epithelium of IFNT-infused ewes receiving P4. Expression ofCOL3A1, SPARC, ACTA2, andTAGLNwas independent of pregnancy, P4, or IFNT.POSTNmRNA was detected primarily in compact stroma of intercaruncular and caruncular endometria, but not in the conceptus. EndometrialPOSTNmRNA increased between days 12 and 14 in pregnant but not cyclic ewes, andPOSTNmRNA was more abundant in uterine stroma of ewes treated with P4. POSTN protein was detected in uterine flushings of pregnant ewes and found to mediate attachment and stimulate migration of ovine trophectoderm cellsin vitro. These results support the ideas that POSTN and S100A2 are regulated by P4and IFNT respectively, and that POSTN is involved in conceptus elongation during early pregnancy.

Discovery of candidate genes and pathways in the endometrium regulating ovine blastocyst growth and conceptus elongation

Establishment of pregnancy in ruminants requires blastocyst growth to form an elongated conceptus that produces interferon tau, the pregnancy recognition signal, and initiates implantation. Blastocyst growth and development requires secretions from the uterine endometrium. An early increase in circulating concentrations of progesterone (P4) stimulates blastocyst growth and elongation in ruminants. This study utilized sheep as a model to identify candidate genes and regulatory networks in the endometrium that govern preimplantation blastocyst growth and development. Ewes were treated daily with either P4 or corn oil vehicle from day 1.5 after mating to either day 9 or day 12 of pregnancy when endometrium was obtained by hysterectomy. Microarray analyses revealed many differentially expressed genes in the endometria affected by day of pregnancy and early P4 treatment. In situ hybridization analyses revealed that many differentially expressed genes were expressed in a cell-specific manner within the endometrium. The Database for Annotation, Visualization, and Integrated Discovery (DAVID) was used to identify functional groups of genes and biological processes in the endometrium that are associated with growth and development of preimplantation blastocysts. Notably, biological processes affected by day of pregnancy and/or early P4 treatment included lipid biosynthesis and metabolism, angiogenesis, transport, extracellular space, defense and inflammatory response, proteolysis, amino acid transport and metabolism, and hormone metabolism. This transcriptomic data provides novel insights into the biology of endometrial function and preimplantation blastocyst growth and development in sheep.

Insulin-like growth factor binding protein-1 in the ruminant uterus: potential endometrial marker and regulator of conceptus elongation

Establishment of pregnancy in ruminants requires conceptus elongation and production of interferon-tau (IFNT), the pregnancy recognition signal that maintains ovarian progesterone (P4) production. These studies determined temporal and spatial alterations in IGF binding protein (IGFBP)-1 and IGFBP3 in the ovine and bovine uterus; effects of P4 and IFNT on their expression in the ovine uterus; and effects of IGFBP1 on ovine trophectoderm cell proliferation, migration, and attachment. IGFBP1 and IGFBP3 were studied because they are the only IGFBPs specifically expressed by the endometrial luminal epithelia in sheep. In sheep, IGFBP1 and IGFBP3 expression was coordinate with the period of conceptus elongation, whereas only IGFBP1 expression was coordinate with conceptus elongation in cattle. IGFBP1 mRNA in the ovine endometria was between 5- and 29-fold more abundant between d 12 and 16 of pregnancy compared with the estrous cycle and greater on d 16 of pregnancy than nonpregnancy in the bovine uterus. In sheep, P4 induced and IFNT stimulated expression of IGFBP1 but not IGFBP3; however, the effect of IFNT did not mimic the abundant increase observed in pregnant ewes. Therefore, IGFBP1 expression in the endometrium is regulated by another factor from the conceptus. IGFBP1 did not affect the proliferation of ovine trophectoderm cells in vitro but did stimulate their migration and mediate their attachment. These studies reveal that IGFBP1 is a common endometrial marker of conceptus elongation in sheep and cattle and most likely regulates conceptus elongation by stimulating migration and attachment of the trophectoderm.

HSD11B1, HSD11B2, PTGS2, and NR3C1 expression in the peri-implantation ovine uterus: effects of pregnancy, progesterone, and interferon tau

Establishment of pregnancy in ruminants requires conceptus elongation and production of interferon tau (IFNT), the pregnancy recognition signal that maintains the corpus luteum and progesterone (P4) secretion. The enzymes hydroxysteroid (11-beta) dehydrogenase 1 (HSD11B1) and HSD11B2 catalyze the interconversion of inactive cortisone and active cortisol, which is a biologically active glucorticoid and ligand for the receptor subfamily 3, group C, member 1 (glucocorticoid receptor) (NR3C1). The activity of HSD11B1 is stimulated by P4, prostaglandins, and cortisol. These studies determined the effects of pregnancy, P4, and IFNT on HSD11B1, HSD11B2, prostaglandin-endoperoxide synthase 2 (prostaglandin G/H synthase and cyclooxygenase) (PTGS2), and nuclear NR3C1 in the ovine uterus. Endometrial HSD11B1 mRNA levels were more abundant between Days 12 and 16 of pregnancy than the estrous cycle, and HSD11B1 and PTGS2 expression in the endometrial luminal and superficial glandular epithelia was coincident with conceptus elongation. HSD11B1 mRNA was very low in the conceptus, whereas HSD11B2 mRNA was abundant in the conceptus but not in the uterus. Treatment of ewes with P4 induced, and intrauterine infusions of IFNT modestly stimulated, HSD11B1 expression in the endometrial luminal and superficial glandular epithelia. In all of the studies, HSD11B1 and PTGS2 expression was coincident in the endometrial epithelia, and NR3C1 was present in all endometrial cell types. Collectively, these results support hypotheses that endometrial epithelial HSD11B1 expression is induced by P4 as well as stimulated by IFNT and PTGS2-derived prostaglandins and that HSD11B1-regenerated cortisol acts via NR3C1 to regulate ovine endometrial functions during early pregnancy.

Comparative aspects of implantation

Uterine receptivity to implantation of blastocysts in mammals includes hatching from zona pellucida, precontact with uterine luminal (LE) and superficial glandular (sGE) epithelia and orientation of blastocyst, apposition between trophectoderm and uterine LE and sGE, adhesion of trophectoderm to uterine LE/sGE, and, in some species, limited or extensive invasion into the endometrial stroma and induction of decidualization of stromal cells. These peri-implantation events are prerequisites for pregnancy recognition signaling, implantation, and placentation required for fetal-placental growth and development through the remainder of pregnancy. Although there is a range of strategies for implantation in mammals, a common feature is the requirement for progesterone (P(4)) to downregulate expression of its receptors in uterine epithelia and P(4) prior to implantation events. P(4) then mediates its effects via growth factors expressed by stromal cells in most species; however, uterine luminal epithelium may express a growth factor in response to P(4) and/or estrogens in species with a true epitheliochorial placenta. There is also compelling evidence that uterine receptivity to implantation involves temporal and cell-specific expression of interferon (IFN)-stimulated genes that may be induced directly by an IFN or induced by P(4) and stimulated by an IFN. These genes have many roles including nutrient transport, cellular remodeling, angiogenesis and relaxation of vascular tissues, cell proliferation and migration, establishment of an antiviral state, and protection of conceptus tissues from challenges by the maternal immune cells.

Local and systemic effects of embryos on uterine tissues during early pregnancy in pigs

In the pig, the periimplantation period is critical for successful establishment of pregnancy. We studied the influence of embryos on oxytocin (OT) and progesterone (P(4)) regulated endometrial and myometrial secretion of 1) luteotrophic prostaglandin E(2) (PGE(2)) and 2) luteolytic prostaglandin F(2alpha) and its metabolite (PGFM) on days 12-14 of pregnancy in pigs. We used unilaterally pregnant pigs created by a surgical procedure in which one uterine horn remained intact and the second horn was cut transversely so that part of the horn was detached from the uterine body. The animals were divided into two groups, inseminated gilts (days 12-14 of pregnancy, n=6) and uninseminated cyclic gilts, which were used as controls (days 12-14 of estrous cycle, n=5). Embryos developed only in the patent part of the uterus and not in the occluded horn. The abundance of OTR mRNA was increased in the endometrium and decreased in the myometrium of the gravid uterine horn in the pregnant pigs compared with the non-gravid uterine horn or either uterine horn in the cyclic pigs, indicative of a local effect of the conceptus. The presence of embryos in the uterine horn during the periimplantation period determines endometrial metabolism of PGF(2alpha) and the local response of the endometrium to OT and P(4). OT stimulates PGF(2alpha) secretion and PGFM accumulation in endometrial cultures only from the non-gravid uterine horn and controls PGE(2) secretion from the endometrium and myometrium in the pregnant gilts. The results indicate a more systemic affect of pregnancy on the uterine response to OT and a possibly the local effect of the conceptus in promoting progesterone's inhibition of OT-stimulated PGE(2) secretion and uterine metabolism of PGF(2alpha).

Interferon regulatory factor 6 (IRF6) is expressed in the ovine uterus and functions as a transcriptional activator

Interferon tau (IFNT), the maternal recognition of pregnancy signal in sheep and other ruminants, is secreted by the conceptus and regulates the expression of a number of genes in a cell-specific manner within the uterus. The response of different endometrial cell types to IFNT appears to be specified by IFN regulatory factors (IRFs). IRF2, a potent repressor of gene transcription, is expressed only by luminal (LE) and superficial glandular epithelia (sGE), whereas IRF1 and IRF9, activators of gene transcription, are expressed only in GE and stromal cells of the uterus during early pregnancy. In the present study, IRF6 was found to be expressed in LE/sGE and middle GE of the ovine uterine endometrium as well as conceptus trophectoderm. IRF family members can regulate transcription via IFN-stimulated response elements (ISREs). Transient transfection analyses found that IRF6 enhanced basal activity of ISRE-containing promoters, but did not enhance IFNT stimulation of ISRE-containing promoters in variety of different cell types. Further, IRF6 did not cooperate with IRF1 or reduce IRF2 repression of ISRE-containing promoter activity. These results establish that IRF6 is a transcriptional activator that is preferentially expressed in the endometrial epithelia and conceptus trophectoderm. IRF6 is hypothesized to play critical roles in endometrial gene expression as well as in conceptus trophectoderm growth and differentiation.

Stanniocalcin 1 is a luminal epithelial marker for implantation in pigs regulated by progesterone and estradiol

Stanniocalcin 1 (STC1) is a glycoprotein that decreases calcium and increases phosphate in cells/tissues. This investigation examined endocrine regulation of STC1 in endometria of pigs during the estrous cycle and pregnancy. STC1 mRNA was present exclusively in luminal epithelium (LE) between d 12 and 15 of the estrous cycle, increased between d 12 and d 20, and was not detectable by d 30 of pregnancy. STC1 protein was also detected in uterine flushings. To determine effects of estrogen and progesterone, pigs were ovariectomized and treated with these hormones alone or together. Progesterone, but not estrogen, induced STC1 in LE. Cotreatment with progesterone and estrogen further stimulated STC1 over progesterone alone. To determine effects of pseudopregnancy, nonpregnant gilts were given daily injections of estradiol benzoate from d 11 to d 14. STC1 was not expressed in LE on d 90 of pseudopregnancy, suggesting that the estradiol given to induce pseudopregnancy and/or long-term exposure to progesterone are required for down-regulation of STC1. To determine effects of long-term progesterone, without effects of estradiol, pigs were ovariectomized on d 12, given daily injections of progesterone through d 39, and hysterectomized on d 40 after estrus. STC1 was expressed in LE of progesterone-treated pigs, suggesting that estrogen is involved in down-regulation of STC1. We conclude that STC1 is induced in LE by progesterone and further stimulated by estrogen, and its down-regulation in LE by d 25 likely requires exposure of the progestinized uterus to estrogen. The temporal and cell type-specific expression of STC1 makes this gene a unique marker for implantation in pigs.

Progesterone and interferon tau regulate leukemia inhibitory factor receptor and IL6ST in the ovine uterus during early pregnancy

The actions of leukemia inhibitory factor (LIF) via LIF receptor (LIFR) and its co-receptor, IL6 signal transducer (IL6ST), are implicated in uterine receptivity to conceptus implantation in a number of species including sheep. The present study determined the effects of the estrous cycle, pregnancy, progesterone (P4), and interferon tau (IFNT) on the expression of LIFR and IL6ST in the ovine uterus. LIFR mRNA and protein were localized to the endometrial luminal (LE) and superficial glandular epithelia (sGE), whereas IL6ST mRNA and protein were localized primarily in the middle to deep GE. Both LIFR and IL6ST mRNAs and protein were more abundant in pregnant than cyclic ewes and increased from days 10 to 20 of pregnancy. Treatment of ovariectomized ewes with P4 and/or infusion of ovine IFNT increased LIFR and IL6ST in endometrial LE/sGE and GE respectively. Co-expression of LIFR and IL6ST as well as phosphorylated STAT3 was observed only in the upper GE of the endometrium as well as in the conceptus trophectoderm on days 18 and 20. In mononuclear trophectoderm and GE cells, LIF elicited an increase in phosphorylated STAT3 and MAPK3/1 MAPK proteins. Collectively, these results suggest that LIFR and IL6ST are both stimulated by IFNT and regulated by P4 in a complex stage- and cell-specific manner, and support the hypothesis that LIF exerts effects on the endometrial GE as well as conceptus trophectoderm during early pregnancy in sheep. Thus, LIF and STAT3 may have biological roles in endometrial function and trophectoderm growth and differentiation.

Dynamic changes in messenger RNA profiles of bovine endometrium during the oestrous cycle

During the oestrous cycle, the bovine endometrium exhibits characteristic morphological and functional changes, which are mainly induced by progesterone (P(4)), oestrogens and oxytocin. We studied the response of the endometrium to this changing hormonal environment at the transcriptome level using a custom-made cDNA microarray. Endometrium samples were recovered from Simmental heifers on days 0 (oestrus), 3.5 (metoestrus), 12 (dioestrus) and 18. The latter group was divided into animals with high (late dioestrus) and low P(4) levels (preoestrus). Significance analysis of microarrays revealed 269 genes exhibiting significant changes in their transcript levels during the oestrous cycle in distinct temporal patterns. Two major types of expression profiles were observed, which showed the highest mRNA levels during the oestrus phase or the highest levels during the luteal phase respectively. A minor group of genes exhibited the highest mRNA levels on day 3.5. Gene ontology (GO) analyses revealed GO categories related to extracellular matrix remodelling, transport, and cell growth and morphogenesis enriched at oestrus, whereas immune response and particular metabolic pathways were overrepresented at dioestrus. Generation of gene interaction networks uncovered the genes possibly involved in endometrial remodelling (e.g. collagen genes, TNC, SPARC, MMP2, MEP1B, TIMP1, TIMP2, HTRA1), regulation of angiogenesis (e.g. ANGPTL2, TEK, NPY, AGT, EPAS1, KLF5 ), regulation of invasive growth (e.g. PCSK5, tight junction proteins, GRP, LGALS1, ANXA2, NOV, PLAT, MET, TDGF1, CST6, ITGB4), cell adhesion (e.g. MUC16, LGALS3BP) and embryo feeding (e.g. SLC1A1, SLC11A2, SLC16A1, SEPP1, ENPP1). Localisation of mRNA expression in the endometrium was analysed for CLDN4, CLDN10, TJP1, PCSK5, MAGED1, and LGALS1.

Progesterone regulates FGF10, MET, IGFBP1, and IGFBP3 in the endometrium of the ovine uterus

Progesterone (P4) is unequivocally required to maintain a uterine environment conducive to pregnancy. This study investigated the effects of P4 treatment on expression of selected growth factors (fibroblast growth factor 7 [FGF7], FGF10, hepatocyte growth factor [HGF], and insulin-like growth factors [IGF1 and IGF2]), their receptors (MET, FGFR2(IIIB), and IGF1R), and IGF binding proteins (IGFBPs) in the ovine uterus. Ewes received daily injections of corn oil vehicle (CO) or 25 mg of P4 in vehicle from 36 h after mating (Day 0) to hysterectomy on Day 9 or Day 12. Another group received P4 to Day 8 and 75 mg of mifepristone (RU486, a P4 receptor antagonist) from Day 8 through Day 12. Endometrial FGF10 mRNA levels increased between Day 9 and Day 12 and in response to P4 on Day 9 in CO-treated ewes, which had larger blastocysts, and were substantially reduced in P4+RU486-treated ewes, which had no blastocysts on Day 12. Endometrial FGF7 or HGF mRNA levels were not affected by day or reduced by RU486 treatment, but MET mRNA levels were higher in P4-treated ewes on Day 9 and Day 12. Levels of IGF1, IGF2, and IGF1R mRNA in the endometria were not affected by early P4 treatment. Although stromal IGFBPs were unaffected by P4, levels of IGFBP1 and IGFBP3 mRNA in uterine luminal epithelia were increased substantially between Day 9 and Day 12 of pregnancy in CO-treated ewes and on Day 9 in early P4-treated ewes. Therefore, FGF10, MET, IGFBP1, and IGFBP3 are P4-regulated factors within the endometrium of the ovine uterus that have potential effects on endometrial function and peri-implantation blastocyst growth and development.

Progesterone and placentation increase secreted phosphoprotein one (SPP1 or osteopontin) in uterine glands and stroma for histotrophic and hematotrophic support of ovine pregnancy

Secreted phosphoprotein one (SPP1, osteopontin) may regulate conceptus implantation and placentation. We investigated effects of progesterone (P(4)) and the conceptus on expression and localization of SPP1 in the ovine uterus. Steady-state levels of SPP1 mRNA in the endometrium of unilaterally pregnant ewes did not differ significantly between nongravid and gravid horns within their respective days of pregnancy; however, levels did increase as pregnancy progressed. SPP1 mRNA was detectable in the glandular epithelium (GE) of both nongravid and gravid horns via in situ hybridization. SPP1 protein was localized to the apical surface of the luminal epithelium of both nongravid and gravid uterine horns. Gravid horns exhibited extensive stromal SPP1 on Days 40 through 120, whereas SPP1 was markedly lower in the stroma of nongravid uterine horns through Day 80 of pregnancy. By Day 120, stromal expression of SPP1 between nongravid and gravid horns was similar. Long-term P(4) treatment of ovariectomized ewes induced SPP1 in the uterine stroma and GE. A bioactive 45-kDa SPP1 fragment was purified from uterine secretions and promoted ovine trophectoderm cell attachment in vitro. Interestingly, increased stromal cell expression of SPP1 was positively associated with vascularization as assessed by von Willebrand factor staining. Finally, ovine uterine artery endothelial cells produced SPP1 during outgrowth into three-dimensional collagen matrices in an in vitro model system that recapitulates angiogenesis. Collectively, P(4) induces and the conceptus further stimulates SPP1 in uterine GE and stroma, where SPP1 likely influences histotrophic and hematotrophic support of conceptus development.

Gastrin-releasing peptide (GRP) in the ovine uterus: regulation by interferon tau and progesterone

Gastrin-releasing peptide (GRP) is abundantly expressed by endometrial glands of the ovine uterus and processed into different bioactive peptides, including GRP1-27, GRP18-27, and a C-terminus, that affect cell proliferation and migration. However, little information is available concerning the hormonal regulation of endometrial GRP and expression of GRP receptors in the ovine endometrium and conceptus. These studies determined the effects of pregnancy, progesterone (P4), interferon tau (IFNT), placental lactogen (CSH1), and growth hormone (GH) on expression of GRP in the endometrium and GRP receptors (GRPR, NMBR, BRS3) in the endometrium, conceptus, and placenta. In pregnant ewes, GRP mRNA and protein were first detected predominantly in endometrial glands after Day 10 and were abundant from Days 18 through 120 of gestation. Treatment with IFNT and progesterone but not CSH1 or GH stimulated GRP expression in the endometrial glands. Western blot analyses identified proGRP in uterine luminal fluid and allantoic fluid from Day 80 unilateral pregnant ewes but not in uterine luminal fluid of either cyclic or early pregnant ewes. GRPR mRNA was very low in the Day 18 conceptus and undetectable in the endometrium and placenta; NMBR and BRS3 mRNAs were undetectable in ovine uteroplacental tissues. Collectively, the present studies validate GRP as a novel IFNT-stimulated gene in the glands of the ovine uterus, revealed that IFNT induction of GRP is dependent on P4, and found that exposure of the ovine uterus to P4 for 20 days induces GRP expression in endometrial glands.

Progesterone and interferon tau regulate hypoxia-inducible factors in the endometrium of the ovine uterus

In ruminants, progesterone (P4) from the ovary and interferon tau (IFNT) from the elongating blastocyst regulate expression of genes in the endometrium that are hypothesized to be important for uterine receptivity and blastocyst development. These studies determined effects of the estrous cycle, pregnancy, P4, and IFNT on hypoxia-inducible factor (HIF) expression in the ovine uterus. HIF1A mRNA, HIF2A mRNA, and HIF2A protein were most abundant in the endometrial luminal and superficial glandular epithelia (LE and sGE, respectively) of the uterus and conceptus trophectoderm. During the estrous cycle, HIF1A and HIF2A mRNA levels were low to undetectable on d 10 in the endometrial LE/sGE, increased between d 10 and 14, and then declined on d 16. Both HIF1A and HIF2A mRNA were more abundant in the endometrial LE/sGE of pregnant ewes. However, HIF3A, HIF1B, HIF2B, and HIF3B mRNA abundance was low in most cell types of the endometria and conceptus. Treatment of ovariectomized ewes with P4 induced HIF1A and HIF2A in the endometrial LE/sGE, and intrauterine infusion of ovine IFNT further increased HIF2A in P4-treated ewes, but not in ewes treated with P4 and the antiprogestin ZK 136,317. HIF3A, HIF1B, HIF2B, and HIF3B mRNA abundance was not regulated by either P4 or IFNT. Two HIF-responsive genes, carboxy-terminal domain 2 and vascular endothelial growth factor A, were detected in both the endometrium and conceptus. These studies identified new P4-induced (HIF1A and HIF2A) and IFNT-stimulated (HIF2A) genes in the uterine LE/sGE, and implicate the HIF pathway in regulation of endometrial epithelial functions and angiogenesis, as well as peri-implantation blastocyst development.

Genes involved in conceptus–endometrial interactions in ruminants: insights from reductionism and thoughts on holistic approaches

This review summarizes new knowledge on expression of genes and provides insights into approaches for study of conceptus–endometrial interactions in ruminants with emphasis on the peri-implantation stage of pregnancy. Conceptus–endometrial interactions in ruminants are complex and involve carefully orchestrated temporal and spatial alterations in gene expression regulated by hormones from the ovary and conceptus. Progesterone is the hormone of pregnancy and acts on the uterus to stimulate blastocyst survival, growth, and development. Inadequate progesterone levels or a delayed rise in progesterone is associated with pregnancy loss. The mononuclear trophectoderm cells of the elongating blastocyst synthesize and secrete interferon-τ (IFNT), the pregnancy recognition signal. Trophoblast giant binucleate cells begin to differentiate and produce hormones including chorionic somatomammotropin 1 (CSH1 or placental lactogen). A number of genes, induced or stimulated by progesterone, IFNT, and/or CSH1 in a cell-specific manner, are implicated in trophectoderm adhesion to the endometrial luminal epithelium and regulation of conceptus growth and differentiation. Transcriptional profiling experiments are beginning to unravel the complex dynamics of conceptus–endometrial interactions in cattle and sheep. Future experiments should incorporate physiological models of pregnancy loss and be complemented by metabolomic studies of uterine lumen contents to more completely define factors required for blastocyst survival, growth, and implantation. Both reduction and holistic approaches will be important to understand the multifactorial phenomenon of recurrent pregnancy loss and provide a basis for new strategies to improve pregnancy outcome and reproductive efficiency in cattle and other domestic animals.

Progesterone regulation of the endometrial WNT system in the ovine uterus

WNT signalling regulates cell proliferation, differentiation, polarity and organisation. The present study investigated the effects of progesterone (P4) on the endometrial WNT system in relation to blastocyst development and growth in sheep. Ewes received daily intramuscular injections of either corn oil (CO) vehicle or 25 mg P4 from 36 h after mating (Day 0) until hysterectomy on Day 9 or 12. Another group received P4 until Day 8 and 75 mg mifepristone (RU486) from Day 8 to Day 12. Early P4 treatment increased blastocyst growth on Days 9 and 12, whereas no blastocysts were recovered from P4 + RU486-treated ewes. Levels of WNT2 mRNA in the stroma and WNT11 and WNT7A mRNAs in the endometrial luminal epithelia (LE) were reduced in P4 + RU486-treated ewes on Day 9, whereas WNT11 mRNA was reduced in the endometria of both P4- and P4 + RU486-treated ewes on Day 12. On Day 12, WNT2 mRNA was increased in the stroma, WNT7A mRNA was increased in the LE and WNT5A mRNA was increased in the LE and stroma of P4 + RU486- compared with P4-treated ewes. DKK1 mRNA was absent in the endometrial stroma of P4 + RU486-treated ewes. Expression of transcription factor 7 like-2 (TCF7L2) was transiently increased in endometrial epithelia of P4-treated ewes on Day 9, but decreased in these ewes on Day 12. MSX1 mRNA was decreased by P4 treatment on Day 9 and levels of both MSX1 and MSX2 mRNA were higher in P4 + RU486-treated ewes on Day 12. Thus, P4 modulates the endometrial WNT system and elicits a transient decline in selected WNT pathways and signalling components, which is hypothesised to alter tight and adherens junctions, thereby stimulating blastocyst growth and development.

Ovarian follicular cells have innate immune capabilities that modulate their endocrine function

Oestrogens are pivotal in ovarian follicular growth, development and function, with fundamental roles in steroidogenesis, nurturing the oocyte and ovulation. Infections with bacteria such as Escherichia coli cause infertility in mammals at least in part by perturbing ovarian follicle function, characterised by suppression of oestradiol production. Ovarian follicle granulosa cells produce oestradiol by aromatisation of androstenedione from the theca cells, under the regulation of gonadotrophins such as FSH. Many of the effects of E. coli are mediated by its surface molecule lipopolysaccharide (LPS) binding to the Toll-like receptor-4 (TLR4), CD14, MD-2 receptor complex on immune cells, but immune cells are not present inside ovarian follicles. The present study tested the hypothesis that granulosa cells express the TLR4 complex and LPS directly perturbs their secretion of oestradiol. Granulosa cells from recruited or dominant follicles are exposed to LPS in vivo and when they were cultured in the absence of immune cell contamination in vitro they produced less oestradiol when challenged with LPS, although theca cell androstenedione production was unchanged. The suppression of oestradiol production by LPS was associated with down-regulation of transcripts for aromatase in granulosa cells, and did not affect cell survival. Furthermore, these cells expressed TLR4, CD14 and MD-2 transcripts throughout the key stages of follicle growth and development. It appears that granulosa cells have an immune capability to detect bacterial infection, which perturbs follicle steroidogenesis, and this is a likely mechanism by which ovarian follicle growth and function is perturbed during bacterial infection.

Galectin 15 (LGALS15): A Gene Uniquely Expressed in the Uteri of Sheep and Goats that Functions in Trophoblast Attachment1

Galectins are a family of secreted animal lectins with biological roles in cell adhesion and migration. In sheep, galectin 15 (LGALS15) is expressed specifically in the endometrial luminal (LE) and superficial glandular (sGE) epithelia of the uterus in concert with blastocyst elongation during the peri-implantation period. The present study examined LGALS15 expression in the uterus of cattle, goats, and pigs. Although the bovine genome contains an LGALS15-like gene, expressed sequence tags encoding LGALS15 mRNA were found only for sheep, and full-length LGALS15 cDNAs were cloned only from endometrial total RNA isolated from pregnant sheep and goats, but not pregnant cattle or pigs. Ovine and caprine LGALS15 were highly homologous at the mRNA (95%) and protein (91%) levels, and all contained a conserved carbohydrate recognition domain and RGD recognition sequence for integrin binding. Endometrial LGALS15 mRNA levels increased after Day 11 of both the estrous cycle and pregnancy, and were considerably increased after Day 15 of pregnancy in goats. In situ hybridization detected abundant LGALS15 mRNA in endometrial LE and sGE of early pregnant goats, but not in cattle or pigs. Immunoreactive LGALS15 protein was present in endometrial epithelia and conceptus trophectoderm of goat uteri and detected within intracellular crystal structures in trophectoderm and LE. Recombinant ovine and caprine LGALS15 proteins elicited a dose-dependent increase in ovine trophectoderm cell attachment in vitro that was comparable to bovine fibronectin. These results support the hypothesis that LGALS15 is uniquely expressed in Caprinae endometria and functions as an attachment factor important for peri-implantation blastocyst elongation.

Secretion of estradiol-17beta by porcine endometrium and myometrium during early pregnancy and luteolysis

Past studies of the source of estrogens secreted during maternal recognition of pregnancy in pigs have focused on embryonic rather than uterine origin of these steroids. The present study documents: (1) the expression of the gene CYP 17, encoding cytochrome P450 17alpha-hydroxylase/C(17-20) lyase and (2) the synthesis and secretion of estradiol-17 beta (E(2)) in endometrial and myometrial tissues in gilts. The expression of CYP 17 gene was shown in porcine endometrium and myometrium. Basal endometrial secretion of E(2) was higher in pregnant gilts than in cyclic gilts (days 14-16). The myometrium secreted more E(2) during the expected time of luteolysis compared to early pregnancy. Basal secretion of E(2) during pregnancy was higher from the endometrium than from the myometrium. Conversely, during luteolysis E(2) secretion was higher from the myometrium and lower from the endometrium. In pregnant and cyclic gilts (days 14-16), progesterone (P(4), 10(-5)M) in vitro significantly increased E(2) secretion regardless of reproductive status. Oxytocin (OT, 10(-7)M) had no influence on E(2) secretion and did not change the stimulatory effect of P(4) in both tissues examined. In conclusions: (1) the CYP 17 gene transcript is present in porcine endometrium and myometrium; (2) porcine endometrium and myometrium release E(2) in vitro; (3) the endometrium releases more E(2) than the myometrium during early pregnancy; (4) the myometrium releases E(2) mainly during luteolysis; (5) the endometrium and myometrium can increase E(2) release in vitro if substrate (P(4)) is provided during early pregnancy and luteolysis. These data suggest active estrogen production by the myometrium and endometrium as an alternative source for this signal for recognition of pregnancy in the pig.

Comparative implantation and placentation

In all placental mammals, the establishment of an intimate contact between the embryo and the mother follows a succession of common critical steps whose chronology and timing may considerably vary from species to species. These processes present a great diversity based on the anatomy and the histology of the uterus, the developmental stage of the embryo at the time of implantation, and the endocrine and molecular interactions between the uterine and the embryonic tissues. This paper provides an overview of the general mechanical, endocrinological and cellular aspects involved in implantation in mammals with an emphasis on domestic species.

Galectin 15 (LGALS15) functions in trophectoderm migration and attachment

Galectin 15 (LGALS15) is expressed specifically by the endometrial luminal epithelium (LE) of the ovine uterus in concert with blastocyst growth, elongation, and implantation. LGALS15 contains a predicted carbohydrate recognition domain (CRD) as well as LDV and RGD recognition sequences for integrin binding. Studies tested the hypothesis that LGALS15 is a secreted regulator of blastocyst development, as well as growth, migration, adhesion, and apoptosis of trophoblast. Bovine embryos were produced in vitro by standard conditions, and putative zygotes were cultured in the presence of recombinant ovine LGALS15. Rates of embryo cleavage and blastocyst formation were not affected by LGALS15. LGALS15 moderately increased proliferation of ovine trophectoderm (oTr) cells. Staurosporine elicited apoptosis of oTr cells, which could be partially inhibited by LGALS15. Migration of oTr cells was stimulated by LGALS15 that was dependent on Jun N-terminal kinase (JNK). A dose-dependent increase in oTr cell attachment to LGALS15 was found that could be inhibited by cyclic GRGDS, but not GRADS, peptides. Mutation of the LDVRGD integrin binding sequence of LGALS15 to LADRAD decreased its ability to promote oTr cell attachment, whereas mutation of the CRD had little effect. LGALS15 induced formation of robust focal adhesions in oTr cells that was abolished by mutation of the LDVRGD sequence. Collectively, these results support the hypothesis that LGALS15 stimulates trophectoderm cell migration and attachment via integrin binding and activation which are critical to blastocyst elongation and implantation.

Technical Note: Bovine Oviduct and Endometrium Array Version 1: A Tailored Tool for Studying Bovine Endometrium Biology and Pathophysiology

Fertility problems are the main reason for slaughter of high-performance milk cows, because elongated calving intervals result in financial losses for the farmer and retard genetic progress. Genetic improvement of fertility would be of great benefit, but functional traits for effective selection are missing. Recent advances in functional genomics tools like DNA microarrays could be the key to identify gene expression patterns in the endometrium that correlate with maternal fertility. Therefore, a first version of a bovine oviduct and endometrium cDNA array was established that contains a set of 1,440 cDNA clones and long oligonucleotides representing 950 different genes. The major part of these genes has been identified in a series of differential gene expression studies in endometrium (different stages of the estrous cycle, d 18 pregnant vs. nonpregnant) and in oviduct epithelial cells (different stages of the estrous cycle) using a combination of subtracted cDNA libraries and cDNA array hybridization. Furthermore, cDNA clones of genes, which showed no changes in their mRNA levels in the analyzed tissues, were added as controls. Reproducibility of the array hybridization, a comparison with the Affymetrix bovine genome array, and confirmation of differential gene expression with reverse transcription-quantitative PCR is shown. Potential future applications include systematic studies of interactions between metabolic status and functionality of the endometrium to identify genes that could be used for differential diagnosis of fertility problems. Further, endometrium transcriptome profiles may serve as novel traits to improve fertility by genetic selection.

Pig conceptuses secrete estrogen and interferons to differentially regulate uterine STAT1 in a temporal and cell type-specific manner

Conceptus trophectoderm and uterine luminal epithelial cells interact via endocrine, paracrine, and autocrine modulators to mediate pregnancy recognition and implantation. Pig conceptuses not only release estrogens for pregnancy recognition but also secrete interferons during implantation. Because interferon-stimulated genes are increased by interferons secreted for pregnancy recognition in ruminants, we asked whether the interferon-stimulated gene, STAT1, is up-regulated in pig endometrium by conceptus estrogens and/or interferons. STAT1 expression in response to day of pregnancy, estrogen injection, and intrauterine infusion of conceptus secretory proteins in pigs indicated 1) estrogen increases STAT1 in luminal epithelial cells, 2) conceptus secretory proteins that contain interferons increase STAT1 in stroma, 3) STAT1 increases in close proximity to the conceptus, and 4) early estrogen results in conceptus death and no STAT1 in stroma. The interactions of estrogen and interferons to regulate cell-type-specific expression of STAT1 highlight the complex interplay between endometrium and conceptus for pregnancy recognition and implantation.

Pregnancy and interferon tau regulate RSAD2 and IFIH1 expression in the ovine uterus

Radical S-adenosyl methionine domain containing 2 (RSAD2) encodes a cytoplasmic antiviral protein induced by interferons (IFN). Interferon-induced with helicase C domain 1 (IFIH1) is a RNA helicase involved in innate immune defense against viruses, growth suppression, and apoptosis. Interferon tau (IFNT), a Type I IFN produced by the peri-implantation ruminant conceptus, acts on the uterine endometrium to signal pregnancy recognition and promote receptivity to implantation. Transcriptional profiling identified RSAD2 and IFIH1 as IFNT regulated genes in the ovine uterine endometrium. This study tested the hypothesis that RSAD2 and IFIH1 were induced in the endometrium in a cell type-specific manner by IFNT from the conceptus during early pregnancy. Endometrial RSAD2 and IFIH1 mRNA increased between days 12 and 16 of pregnancy, but not of the estrous cycle. In pregnant ewes, RSAD2 and IFIH1 mRNAs increased in endometrial glands, and stroma and immune cells, but not in the luminal epithelium. Neither gene was expressed in the trophectoderm of day 18 or 20 conceptuses. Progesterone (P4) treatment of ovariectomized ewes did not induce expression RSAD2 or IFIH1 mRNA in the endometrium; however, intrauterine injections of IFNT induced expression of RSAD2 and IFIH1 mRNA in endometria of ewes treated with P4, as well as in ewes treated with P4 and the progesterone receptor antagonist, ZK 136,317. These results indicate that conceptus IFNT induces both RSAD2 and IFIH1 in a P4-independent manner in the ovine uterine endometrium. These two IFNT-stimulated genes are proposed to have biological roles in the establishment of uterine receptivity to the conceptus during implantation through induction of an antiviral state and modulation of local immune cells in the endometrium.

Tight and adherens junctions in the ovine uterus: differential regulation by pregnancy and progesterone

In species with noninvasive implantation by conceptus trophectoderm, fetal/maternal communications occur across the endometrial epithelia. The present studies identified changes in junctional complexes in the ovine endometrium that regulate paracellular trafficking of water, ions, and other molecules, and the secretory capacity of the uterine epithelia. Distinct temporal and spatial alterations in occludin, tight junction protein 2, and claudin 1-4 proteins were observed in the endometrium of cyclic and early pregnant ewes. Dynamic changes in tight junction formation were characterized by an abundance of tight junction proteins on d 10 of the estrous cycle and pregnancy that substantially decreased by d 12. Early progesterone administration advanced conceptus development on d 9 and 12 that was associated with loss of tight-junction-associated proteins. Pregnancy increased tight-junction-associated proteins between d 14-16. Cadherin 1 and beta-catenin, which form adherens junctions, were abundant in the endometrial glands, but decreased after d 10 of pregnancy in the luminal epithelium and then increased by d 16 with the onset of implantation. Results support the ideas that progesterone elicits transient decreases in tight and adherens junctions in the endometrial luminal epithelium between d 10-12 that increases selective serum and tissue fluid transudation to enhance blastocyst elongation, which is subsequently followed by an increase in tight and adherens junctions between d 14-16 that may be required for attachment and adherence of the trophectoderm for implantation. The continuous presence of tight and adherens junctions in the uterine glands would allow for vectorial secretion of trophic substances required for conceptus elongation and survival.

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.

Regulation of Expression of Fibroblast Growth Factor 7 in the Pig Uterus by Progesterone and Estradiol1

Fibroblast growth factor 7 (FGF7) stimulates cell proliferation, differentiation, migration and angiogenesis. The consensus is that FGF7, expressed by mesenchymal cells, binds FGF receptor 2IIIb (FGFR2) on epithelia, thereby mediating epithelial-mesenchymal interactions. The pig uterus is unique in that FGF7 is expressed by the luminal epithelium (LE) and FGFR2 is expressed by the LE, glandular epithelium (GE), and trophectoderm to effect proliferation and differentiated cell functions during conceptus development and implantation. FGF7 expression by the uterine LE of pigs increases between Days 9 and 12 of the estrus cycle and pregnancy, as circulating concentrations of progesterone increase, progesterone receptors (PGR) in the uterine epithelia decrease, and the conceptuses secrete estradiol-17beta (E(2)), for pregnancy recognition. Furthermore, E(2) increases the expression of FGF7 in pig uterine explants. The present study investigates the relationships between progesterone, E(2), and their receptors and the expression of FGF7 in the pig uterus in vivo. Pigs were ovariectomized on Day 4 of the estrus cycle and injected i.m. daily from Day 4 to Day 12 with either corn oil (CO), progesterone (P4), P4 and ZK317,316 (PZK), E(2), P4 and E(2) (PE), or P4 and ZK and E(2) (PZKE). All gilts (n = 5/treatment) were hysterectomized on Day 12. The results suggest that: 1) P4 is permissive to FGF7 expression by down-regulating PGR in LE; 2) P4 stimulates PGR-positive uterine stromal cells to release an unidentified progestamedin that induces FGF7 expression by LE; 3) E(2) and P4 can induce FGF7 when PGR are rendered nonfunctional by ZK; and 4) E(2) from conceptuses interacts via estrogen receptor alpha, but not estrogen receptor beta in LE to induce maximal expression of FGF7 in LE on Day 12 of pregnancy in pigs.

Pregnancy recognition and conceptus implantation in domestic ruminants: roles of progesterone, interferons and endogenous retroviruses

The present review highlights new information on pregnancy recognition and conceptus development and implantation in sheep with respect to regulation by progesterone, interferons and endogenous retroviruses. After formation of the corpus luteum, progesterone acts on the endometrium and stimulates blastocyst growth and elongation to a filamentous conceptus (embryo/fetus and associated extra-embryonic membranes). The envelope of endogenous retroviruses related to Jaagsiekte sheep retroviruses appears to intrinsically regulate mononuclear trophectoderm cell proliferation and differentiation into trophoblast giant binucleate cells. The mononuclear trophectoderm cells of elongating sheep conceptuses secrete interferon-tau, which acts on the endometrium to prevent development of the luteolytic mechanism by inhibiting transcription of the gene for the oestrogen receptor alpha in the luminal and superficial ductal glandular epithelia. These actions prevent oestrogen-induced transcription of the oxytocin receptor gene and, therefore, oxytocin-induced luteolytic pulses of prostaglandin F2alpha. Progesterone down regulation of its receptors in luminal and glandular epithelia correlates temporally with a reduction in anti-adhesive mucin land induction of secreted galectin 15 (LGALSI5) and secreted phosphoprotein 1, which are proposed to regulate trophectoderm proliferation and adhesion. Interferon-c acts on the endometrial lumenal epithelium to induce WNT7A and to stimulate LGALS 15, cathepsin L and cystatin C, which are candidate regulators of conceptus development and implantation. The number of potential contributors to maternal recognition and establishment of pregnancy continues to grow and this highlights our limited appreciation of the complexity of the key molecules and signal transduction pathways that intersect during these key developmental processes. The goal of improving reproductive efficiency by preventing embryonic losses that occur during the peri-implantation period of pregnancy in domestic ruminants provides the challenge to increase our knowledge of endometrial function and conceptus development.

Human early placental development: potential roles of the endometrial glands

There is strong evidence that the endometrial glands play a key role in regulating placental development in many domestic species, but their contribution in the human has largely been ignored once implantation is complete. Here we re-evaluate their role during the first trimester. Connections between the glands and the intervillous space have been observed from day 17 post-conception through to the end of the first trimester. In the absence of a maternal arterial supply to the early placenta it is believed that the carbohydrate- and lipid-rich secretions represent an important source of nutrients during the first trimester, and possibly the beginning of the second trimester. The secretions also contain a variety of growth factors that may regulate placental morphogenesis since their receptors are present on villous and extravillous trophoblast, and villous endothelial cells. Other components of the secretions may modulate immune responses and trophoblast invasion at the materno-fetal interface. We speculate that lactogenic hormones secreted by decidual cells and the syncytiotrophoblast may act in concert with human chorionic gonadotropin to stimulate the secretory activity of glandular epithelial cells during the first trimester. There is circumstantial evidence, but as yet no conclusive proof, that deficient glandular activity is associated with pregnancy failure in the human.

Developmental regulation of prostacyclin synthase and prostacyclin receptors in the ovine uterus and conceptus during the peri-implantation period

This study documents the expression of prostacyclin (PGI2) synthase (PTGIS) and PGI2 receptors in the trophoblast and uterus of the ewe at the time of maternal recognition of pregnancy (i.e. days 7, 9, 12, 14 and 17). The membrane receptor for PGI2 (PTGIR) and the nuclear receptors, i.e. peroxisome proliferator-activated receptors (PPAR) and their heterodimer partners the retinoid X receptors (RXR), were analysed. In the endometrium, PTGIS transcript and protein were expressed at day 9 of pregnancy and levels declined from days 12 to 17. Immunohistochemistry and in situ hybridization indicated that PTGIS was mainly located in the luminal epithelium of the endometrium. Endometrial PTGIR, PPARA, PPARG and RXRG expression was regulated during the peri-implantation period whereas PPARD, RXRA and RXRB were consistently expressed. In the trophoblast, PTGIS transcript levels rose as development progressed and peaked at day 17. PTGIR and PPARA transcripts peaked before day 12 and then declined and became nearly undetectable by day 17, whereas PPARD and PPARG transcript levels rose steadily from days 12 to 17. Because the PPARs and the RXRs display different expression profiles, we suggest that different heterodimers may form and support distinct functions as development proceeds. Our results also underline the importance of PTGIS and PPARD in the trophoblast and PTGIR in the uterus, suggesting that PGI2 is of both uterine and trophoblastic origin and is involved in a complex signalling pathway at around the time of implantation in the ewe.

Progesterone Regulation of Preimplantation Conceptus Growth and Galectin 15 (LGALS15) in the Ovine Uterus1

Peri-implantation conceptus (embryo/fetus and associated extraembryonic membranes) growth and development are primarily regulated by secretions from the uterus. This study investigated the effects of progesterone on preimplantation conceptus development and endometrial galectin 15 (LGALS15). Ewes received daily injections of either corn oil (CO) vehicle or 25 mg progesterone (P4) from 36 h postmating to hysterectomy. Treatment with P4 increased blastocyst diameter by 220% on Day 9 and advanced time of elongation of blastocysts to a filamentous conceptus on Day 12. Effects of P4 treatment on blastocyst development were blocked by administration of RU486, a progesterone receptor antagonist. Consistent with early elongation of blastocysts, interferon tau (IFNT) protein was about 50-fold greater in uterine flushes from Day 12 in ewes receiving P4 compared with those receiving CO. Expression of cathepsin L (CTSL) and radical S-adenosyl methionine domain containing 2 (RSAD2), both IFNT-stimulated genes, was increased in endometria of Day 12 P4-treated ewes. LGALS15 mRNA, expressed only in the endometrial luminal epithelium and superficial glands, was detected between Days 9 and 12 and was more abundant in ewes receiving P4 than in those receiving CO on both Days 9 and 12. RU486 treatment ablated P4 induction of LGALS15 mRNA in the endometrial epithelia. LGALS15 protein in uterine flushings was not different on Day 9 but tended to be greater in P4-treated ewes than in those receiving CO on Day 12. The advanced development of blastocysts in P4-treated ewes is hypothesized to involve early induction of specific genes in the endometrial epithelia, such as LGALS15, and undoubtedly components of uterine histotroph.

Progesterone and interferon-tau regulate cystatin C in the endometrium

Cystatin C (CST3) is a secreted inhibitor of lysosomal cysteine proteases cathepsins B (CTSB) and CTSL, which are abundant in the ovine endometrium and conceptus. In mice, cathepsins and cystatins play important roles in implantation and placentation. This study determined effects of the estrous cycle, pregnancy, progesterone (P4), and interferon-tau (IFNT) on CST3 in the ovine uterus. In cyclic ewes, CST3 mRNA was low on d 10, increased about 12-fold by d 12, and declined thereafter. In early pregnant ewes, CST3 mRNA was low on d 10 and increased about 130-fold from d 10 to d 20. CST3 mRNA and protein were abundant in the endometrial luminal epithelium (LE) and glandular epithelium and also in conceptus trophectoderm. In uterine flushes from pregnant ewes, CST3 protein was not detected on d 10 but was abundant on d 12, 14, and 16. In another study, treatment of ovariectomized, cyclic ewes with P4 induced a 14-fold increase in endometrial CST3 mRNA, and IFNT stimulated an additional 2-fold increase in CST3 mRNA in P4-treated ewes but not in ewes treated with P4 and the antiprogestin ZK 136,317. CST3 mRNA and protein were abundant in the endometrial luminal epithelium and superficial glandular epithelium of P4-treated ewes but were very low or not detectable in endometria of P4- and ZK-treated ewes. These results indicate that CST3 is a novel P4-induced and IFNT-stimulated gene expressed only in the epithelial cells of the ovine endometrium and implicate CST3 in regulation of uterine cathepsin activity during conceptus implantation.

Multiplicity of Progesterone's Actions and Receptors in the Mammalian Ovary1

This minireview summarizes the role that progesterone (P4) plays in regulating granulosa and luteal cell function. These actions include the stimulation of P4 synthesis and the inhibition of estrogen synthesis, mitosis, and apoptosis. P4 also plays a key role in the ovulatory process. Although P4's actions are well documented, the mechanism or mechanisms that mediate all of these actions have not been defined. In addition to P4-induced gene transcription that is mediated by the nuclear P4 receptors (PGR-A and PGR-B), three other receptor/signal transduction pathways could account for P4's intraovarian actions. These pathways could be mediated by 1) the PGR localizing at or near the plasma membrane and activating SRC family kinases, 2) a membrane progestin receptor that responds to P4 by lowering intracellular cAMP and increasing MAPK 3/1 activity, and 3) a membrane receptor complex composed of serpine 1 mRNA binding protein (also known as PAIRBP1 or RDA288) and progesterone receptor membrane component 1. Ligand activation of this complex likely leads to an increase in protein kinase G activity, the maintenance of low basal intracellular free calcium, and the inhibition of granulosa and luteal cell mitosis and apoptosis. Given the complexity of P4's actions within the ovary, it is likely that all of these receptor/signal transduction pathways influence some aspect of ovarian function with the specific P4 response dependent on 1) the expression pattern of these putative P4 receptors, 2) the P4 binding affinity of each receptor system, and 3) the amount of available P4.

Trophoblast cells of ruminant placentas—A minireview

The ruminant placenta is classified as cotyledonary and synepitheliochorial on the basis of its gross anatomical features and histological characteristics, respectively. The richly vascularized embryonic chorioallantois is lined on its external surface by cells of the trophectodermal epithelium. These cells which assume specialized functions are referred to as trophoblast cells. Two morphologically and functionally distinct cell types have been recognized in the trophectoderm of the placenta of ruminant animals. These are the mononucleate trophoblast cells and the binucleate trophoblast cells. The occurrence, morphological characteristics, and specialized functions of these trophoblast cells, in relation to conceptus nutrition and survival in utero are discussed in this review.

Stanniocalcin (STC) in the Endometrial Glands of the Ovine Uterus: Regulation by Progesterone and Placental Hormones1

Stanniocalcin (STC) is a hormone in fish that regulates calcium levels. Mammals have two orthologs of STC with roles in calcium and phosphate metabolism and perhaps cell differentiation. In the kidney and gut, STC regulates calcium and phosphate homeostasis. In the mouse uterus, Stc1 increases in the mesometrial decidua during implantation. These studies determined the effects of pregnancy and related hormones on STC expression in the ovine uterus. In Days 10-16 cyclic and pregnant ewes, STC1 mRNA was not detected in the uterus. Intriguingly, STC1 mRNA appeared on Day 18 of pregnancy, specifically in the endometrial glands, increased from Day 18 to Day 80, and remained abundant to Day 120 of gestation. STC1 mRNA was not detected in the placenta, whereas STC2 mRNA was detected at low abundance in conceptus trophectoderm and endometrial glands during later pregnancy. Immunoreactive STC1 protein was detected predominantly in the endometrial glands after Day 16 of pregnancy and in areolae that transport uterine gland secretions across the placenta. In ovariectomized ewes, long-term progesterone therapy induced STC1 mRNA. Although interferon tau had no effect on endometrial STC1, intrauterine infusions of ovine placental lactogen (PL) increased endometrial gland STC1 mRNA abundance in progestinized ewes. These studies demonstrate that STC1 is induced by progesterone and increased by a placental hormone (PL) in endometrial glands of the ovine uterus during conceptus (embryo/fetus and extraembryonic membranes) implantation and placentation. Western blot analyses revealed the presence of a 25-kDa STC1 protein in the endometrium, uterine luminal fluid, and allantoic fluid. The data suggest that STC1 secreted by the endometrial glands is transported into the fetal circulation and allantoic fluid, where it is hypothesized to regulate growth and differentiation of the fetus and placenta, by placental areolae.

Sex steroid receptor expression in the oviduct and uterus of sheep with estrus synchronized with progestagen or prostaglandin analogues

The objective of this study was to investigate differences in the expression of estrogen receptor-alpha (ERalpha), progesterone receptor (PR) and the proliferative indexes (Ki-67), in the uterus and oviduct of sheep with estrus synchronized either by prostaglandin analogues (Group PA, n=27) or by treatment with progestagens (Group P, n=29) on days 4 and 7 (day 0=estrus), when the embryos were collected. Immunohistochemical methods were used to quantify ERalpha, PR and Ki-67 in six superficial and deep compartments in the uterus and oviduct. The expression of ERalpha was significantly (P<0.01) lower in progestagen treated ewes than in prostaglandin analogues treated group in the luminal epithelium, superficial glands and superficial stroma in the uterus on day 4. The expression of PR was significantly lower in progesterone treated ewes than in the PA Group in the superficial gland (P<0.05) in both days studied. The lowest expression of PR was observed in the luminal caruncular epithelium and superficial glands in both treatments, obtaining the lowest levels on day 4 (P<0.05). There were significant differences between days 4 and 7 in the Ki-67 immunostaining in the luminal epithelium (P<0.01) and superficial glands (P<0.05). A higher cell proliferation was observed in the uterine epithelium (P<0.05) on day 4 in the animals treated with progestagens. Results indicate that sheep with synchronization of estrus with progestagens showed a reduction of ERalpha and PR protein expression in most of oviductal and uterine cells.

Estrogen regulates transcription of the ovine oxytocin receptor gene through GC-rich SP1 promoter elements

Establishment of pregnancy in ruminants results from paracrine signaling by interferon tau (IFNT) from the conceptus to uterine endometrial luminal epithelia (LE) that prevents release of luteolytic prostaglandin F(2alpha) pulses. In cyclic and pregnant ewes, progesterone down-regulates progesterone receptor (PGR) gene expression in LE. In cyclic ewes, loss of PGR allows for increases in estrogen receptor alpha (ESR1) and then oxytocin receptor (OXTR) gene expression followed by oxytocin-induced prostaglandin F(2alpha) pulses. In pregnant ewes, IFNT inhibits transcription of the ESR1 gene, which presumably inhibits OXTR gene transcription. Alternatively, IFNT may directly inhibit OXTR gene transcription. The 5' promoter/enhancer region of the ovine OXTR gene was cloned and found to contain predicted binding sites for activator protein 1, SP1, and PGR, but not for ESR1. Deletion analysis showed that the basal promoter activity was dependent on the region from -144 to -4 bp that contained only SP1 sites. IFNT did not affect activity of the OXTR promoter. In cells transfected with ESR1, E2, and ICI 182,780 increased promoter activity due to GC-rich SP1 binding sites at positions -104 and -64. Mutation analyses showed that the proximal SP1 sites mediated ESR1 action as well as basal activity of the promoter. In response to progesterone, progesterone receptor B also increased OXTR promoter activity. SP1 protein was constitutively expressed and abundant in the LE of the ovine uterus. These results support the hypothesis that the antiluteolytic effects of IFNT are mediated by direct inhibition or silencing of ESR1 gene transcription, thereby precluding ESR1/SP1 from stimulating OXTR gene transcription.

Placental function in development and disease

The placenta is an organ that clinicians and embryologists would all agree is important for pregnancy success. Unfortunately, however, they too often ignore it when they are exploring causes for embryonic, fetal and perinatal complications. The core function of the placenta is to mediate the transport of nutrients between the maternal and fetal circulation, but it also has critical endocrine functions that alter different maternal physiological systems in order to sustain pregnancy. Both its development and ongoing functions can be dynamically regulated by environmental factors, including nutrient status and tissue oxygenation. In recent years, mainstream attention has begun to shift onto the placenta and it is now becoming clear that placental pathology is associated with several complications in human and animal pregnancies, including embryonic lethality, fetal growth restriction, pre-eclampsia and the high rates of fetal deaths observed after nuclear transfer (cloning).