Comparative aspects of conceptus signals for maternal recognition of pregnancy

Evolutionary Patterns of Maternal Recognition of Pregnancy and Implantation in Eutherian Mammals

The implantation of the embryo into the maternal endometrium is a complex process associated with the evolution of viviparity and placentation in mammals. In this review, we provide an overview of maternal recognition of pregnancy signals and implantation modes in eutherians, focusing on their diverse mechanisms and evolutionary patterns. Different pregnancy recognition signals and implantation modes have evolved in eutherian mammals, reflecting the remarkable diversity of specializations in mammals following the evolution of viviparity. Superficial implantation is the ancestral implantation mode in Eutheria and its major clades. The other modes, secondary, partially, and primary interstitial implantation have each independently evolved multiple times in the evolutionary history of eutherians. Although significant progress has been made in understanding pregnancy recognition signals and implantation modes, there is still much to uncover. Rodents and chiropterans (especially Phyllostomidae) offer valuable opportunities for studying the transitions among implantation modes, but data is still scarce for these diverse orders. Further research should focus on unstudied taxa so we can establish robust patterns of evolutionary changes in pregnancy recognition signaling and implantation modes.

RhoA/ROCK signaling antagonizes bovine trophoblast stem cell self-renewal and regulates preimplantation embryo size and differentiation

Exponential proliferation of trophoblast stem cells (TSC) is crucial in Ruminantia to maximize numerical access to caruncles, the restricted uterine sites that permit implantation. When translating systems biology of the undifferentiated bovine trophectoderm, we uncovered that inhibition of RhoA/Rock promoted self-renewing proliferation and substantially increased blastocyst size. Analysis of transcripts suppressed by Rock inhibition revealed transforming growth factor β1 (TGFβ1) as a primary upstream effector. TGFβ1 treatment induced changes consistent with differentiation in bTSCs, a response that could be replicated by induced expression of the bovine ROCK2 transgene. Rocki could partially antagonize TGFβ1 effects, and TGFβ receptor inhibition promoted proliferation identical to Rocki, indicating an all-encompassing upstream regulation. Morphological differentiation included formation of binucleate cells and infrequent multinucleate syncytia, features we also localize in the in vivo bovine placenta. Collectively, we demonstrate a central role for TGFβ1, RhoA and Rock in inducing bTSC differentiation, attenuation of which is sufficient to sustain self-renewal and proliferation linked to blastocyst size and preimplantation development. Unraveling these mechanisms augments evolutionary/comparative physiology of the trophoblast cell lineage and placental development in eutherians.

The involvement of peroxisome proliferator activated receptors (PPARs) in prostaglandin F2α production by porcine endometrium

In the present study, we investigated the in vitro effects of peroxisome proliferator activated receptor (PPAR) ligands on PGF2α secretion and mRNA expression of prostaglandin F synthase (PGFS) in porcine endometrial explants collected on days 10-12 and 14-16 of the estrous cycle or pregnancy. The explants were incubated for 6h with: PPARα ligands - WY-14643 (agonist) and MK 886 (antagonist); PPARβ ligands - l-165,041 (agonist) and GW 9662 (antagonist); PPARγ ligands - 15d-prostaglandin J2 (PGJ2, agonist), rosiglitazone (agonist) and T0070907 (antagonist). The expression of PGFS mRNA in the endometrium and the concentration of PGF2α in culture media were determined by real time RT-PCR and radioimmunoassay, respectively. During the estrous cycle (days 10-12 and 14-16), the agonists - WY-14643 (PPARα), l-165,041 (PPARβ), PGJ2 and rosiglitazone (PPARγ) - increased PGF2α secretion but did not affect PGFS mRNA abundance. During pregnancy (days 10-12 and 14-16), PPARα and PPARγ ligands did not change PGF2α release, whereas PPARβ agonist augmented PGF2α release on days 14-16 of pregnancy. In addition, WY-14643 and l-165,041 increased PGFS mRNA level in both examined periods of pregnancy. PPARγ agonist (PGJ2) and antagonist (T0070907) enhanced PGFS mRNA abundance in the endometrium on days 10-12 and 14-16 of pregnancy, respectively. The results indicate that PPARs are involved in the production of PGF2α by porcine endometrium, and that the sensitivity of the endometrium to PPAR ligands depends on reproductive status of animals.

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.

Maintenance or interruption of pregnancy by human chorionic gonadotrophin in adrenalectomized albino rats

In the present study, we investigated the efficacy of human chorionic gonadotrophin (HCG) in the maintenance of pregnancy in adrenalectomized rats. Holtzman's strain albino rats were adrenalectomized on day 8 of pregnancy and at the same time were laparotomized to observe the number of implantations. Adrenalectomy on day 8 caused abortions or fetal resorption in almost all rats. Administration of 5 or 50 IU HCG in adrenalectomized rats, from day 8 through 14 or 19, was not able to maintain gestation, resulting in fetal resorption with many placentomas and placental scars. However, a single injection of 5 IU or 1 IU HCG administered on day 8 only maintained the pregnancy to full term in adrenalectomized rats. Hence, the present experiment indicates that replacement therapy of a single dose of 5 IU or 1 IU HCG might be sufficient for maintaining pregnancy in adrenalectomized rats.

Effect of dietary beta-carotene on the early embryonic development and uterine fluid composition of gilts

The role of beta-carotene in reproduction was investigated in gilts assigned to three dietary supplementations: VA (4000 IU vitamin A); VA + VA (4000 IU + 8300 IU); VA + BC (4000 IU + 100 mg beta-carotene) per kg diet for 14 weeks. Gilts were slaughtered at day 12 of gestation. In the VA + BC group, number of corpora lutea was lowest, but the number of embryos was greatest, resulting in a non-significant decreased prenatal mortality (p<0.07). The proportion of less developed spherical and tubular embryos compared with filamentous was greatest in the VA + BC group (p<0.01). No differences were observed for vitamin A and retinal binding protein (RBP) in the uterine fluid. When animals were grouped according to the development of blastocysts, vitamin A and RBP levels were higher in the VA + BC group with only filamentous embryos (p<0.01). This indicates that the supplementation of beta-carotene to gilts might affect embryonic losses possibly because of slower alterations in the uterine environment, resulting in a higher and less variable number of embryos, despite an apparently more heterogeneous development.

Immunohistochemical Studies on Oestrogen Receptor Alpha (ERα) and the Proliferative Marker Ki-67 in the Sow Uterus at Oestrus and Early Pregnancy

Oestrogen receptor alpha (ERalpha), the main subtype in the uterus, is involved in the regulation of uterine growth/proliferation. A relationship between ERalpha and proliferative activity has been shown in the cyclic sow uterus, but to our knowledge, no study has been carried out on early pregnant sows. Therefore, by means of immunohistochemistry and use of mouse monoclonal antibodies to ERalpha and a proliferative marker, Ki-67, the localization of these proteins was investigated in the sow uterus during early pregnancy. Eighteen crossbred multiparous sows were artificially inseminated once at 20-15 h before expected ovulation. After artificial insemination (AI), they were slaughtered at five different times: at oestrus, 5-6 h after AI (n = 4), 20-25 h after ovulation (n =4), 70 h after ovulation (n = 4), on day 11 (the first day of standing oestrus = day 1, n = 3) and on day 19 (n = 3). Immediately after slaughter, uterine samples were collected at the mesometrial side of the uteri, fixed in 10% formaldehyde and embedded in paraffin. Immunohistochemistry was performed by using mouse monoclonal antibodies to ERalpha (C-311) and Ki-67 (MM1). All sows slaughtered after ovulation were pregnant. In general, positive immunostaining for ERalpha and Ki-67 was found in the nuclei. Variations in staining intensity and proportion of positive nuclei were observed in different uterine compartments and stages of early pregnancy. The highest level of ERalpha presence in the surface epithelium and myometrium was found at oestrus (5-6 h after AI), and low levels of ERalpha in these compartments were observed as early as 20-25 h after ovulation. In the glandular epithelia, presence of ERalpha was highest at 70 h after ovulation. The largest number of ERalpha-positive cells in the stroma was observed at oestrus and early after ovulation. Low proliferation was observed, and with no significant difference in tissue compartments except in the glandular epithelium. High proliferative activity in the glandular epithelium at 70 h after ovulation indicated involvement in preparation for secretory activity and growth during pregnancy establishment. Significant positive correlation was found between the number of ERalpha-positive cells in the stroma and Ki-67-positive cells in the surface epithelium. In conclusion, the present study showed differences in immunolocalization of ERalpha and the proliferative marker Ki-67 in different tissue compartments of the sow uterus at oestrus and early pregnancy. In some uterine compartments, the patterns of ERalpha and Ki-67 immunostaining seemed to be influenced by insemination and the presence of embryos, in addition to the effects of steroid hormones.

The role of essential trace elements in embryonic and fetal development in livestock

This review addresses the concept that essential trace minerals play a vital role in many enzymatic and metabolic pathways that are critical for conceptus development during pregnancy in livestock species. The conceptus relies entirely on the maternal system for a sufficient supply of trace minerals and other nutrients needed for normal development. If this supply is inadequate, growth and/or health of the conceptus can be affected adversely, and many of these effects carry over into the neonatal period. Information, accumulated in our laboratory and presented herein, indicates that zinc, copper and manganese are among the trace minerals that have the greatest impact on reproduction. For example, levels of zinc, copper and manganese were several fold greater in the conceptus than in other reproductive tissues, indicating that the conceptus preferentially accumulates these minerals, an action that may be important for conceptus development, growth and survival. Moreover, some recent results indicate that increasing the biological availability of zinc, copper and manganese, by attachment to short peptide chains (i.e., proteinated trace minerals) can enhance reproductive performance of swine. Mineral concentrations in conceptuses from female pigs consuming proteinated trace minerals were greater than those from females that consumed only inorganic mineral salts. Elucidating the mechanisms whereby conceptus development and survival are enhanced by essential trace minerals may lead to development of specific feeding programs to increase the number and health of offspring at parturition, thereby allowing for further improvements in production efficiency in animal agriculture.

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.

Immunocytochemical localization of growth factors and intermediate filaments during the establishment of the porcine placenta

The immunocytochemical localization of insulin-like growth factor I (IGF-I) and platelet-derived growth factor A (PDGF-A) chain ligands, PDGF-chain receptors, and the intermediate filaments cytokeratin, desmin, and vimentin in the tissue reorganization and development during the establishment of the porcine epitheliochorial placenta was studied at light and electron microscopic levels in sections of endometrium and/or placenta of gilts during early pregnancy up to day 40 postmating. The endometrial epithelia (surface and glandular) as well as the trophoblast showed PDGF-A and IGF-I labelling. The only temporal difference was seen regarding IGF-I labelling, this being more uniform in the glands during precontact and early contact stages (days 7-12) compared to later stages. Cytokeratin labelling was conspicuous in all epithelia, including the trophoblast. The endometrial stroma showed strong labelling for the PDGF receptors and the intermediate filament vimentin, staining being enhanced along with the increase in the vascular bed during the establishment of the placenta. The maternal endothelium immunoreacted to IGF-I, to both PDGF-A and PDGF receptors, to vimentin and to von Willebrand factor (Factor VIII). Desmin was also expressed in the capillary bed underneath the maternal surface epithelium. In larger blood vessels, desmin was detected in the smooth muscle layer but not in the endothelium. The vascular smooth muscle also reacted with IGF-I, PDGF-A, and PDGF-receptor antibodies. The results suggest the involvement of both growth factors, IGF-I and PDGF, in the early nutrition of the pig embryo and the tissue reorganization that encompasses placentation. IGF-I appears to be related to the secretory tissue compartment (formation of histotrophe), whereas PDGF might play a role in the reorganization of the stroma, particularly during placental angiogenesis. Desmin and von Willebrand factor immunolabelling appears to be useful to monitor the development of the subepithelial capillary bed in the porcine placenta.

Transfer of heterologous immunoglobulin into the uterine lumen of pigs

Transfer of circulating heterologous immunoglobulin G (IgG) into the uterine lumen of pigs has not been reported. The present study determined if ovine IgG (oIgG) could be transferred into the uterine lumen of pigs. Six gilts (nonparous female pigs) were injected i.v. with either immune sheep serum (25 or 50 ml) to porcine uteroferrin (Uf) or non-immune sheep serum (50 ml) on days 9, 11 and 13 of the estrous cycle. Serum was collected daily from days 9 to 15 and uterine flushings were collected at hysterectomy on day 15. An ELISA detecting oIgG was used to determine levels of oIgG in pig sera and uterine flushings. High oIgG levels in serum (ranging from 87 +/- 11 to 141 +/- 14 micrograms/ml) were maintained by injecting the gilts at 48 h intervals with ovine antiserum to porcine Uf. Serum concentrations of oIgG did not differ (P > 0.05) regardless of whether immune or non-immune sera or different doses of immune serum were injected. oIgG in uterine flushings (2 +/- 1 micrograms/uterine flushing) was detectable when the samples were concentrated 40-fold, but were lower (P < 0.01) than serum levels of oIgG (107 +/- 10 micrograms/ml). Results indicate that small amounts of circulating heterologous IgG can be transferred into the uterine lumen of pigs. However, passive immunization may not result in titers high enough to examine in vivo functions of proteins secreted into the uterine lumen of pigs.

Developmentally regulated expression of interleukin-1 beta by peri-implantation conceptuses in swine

Interleukin-1 beta (IL-1 beta) is one of the critical inflammatory cytokines involved in many physiological processes. This study investigated the temporal expression of IL-1 beta in pig conceptuses. A human IL-1 beta cDNA probe and a anti-human IL-1 beta antibody were used to examine IL-1 beta gene and protein expression in pig conceptuses on days 11, 12, 13, 14, 15, 20, 30, 45, 60, 75, 90, 105 and 112 of pregnancy using Northern, Slot and Western blot analyses. A human cell line (A375.S2) was used to determine IL-1 activity in pig conceptuses. High levels of IL-1 beta mRNA were detected in days 11, 12 and 13 conceptuses. IL-1 beta protein was also detected in conceptuses on days 11, 12, 13, and 14, but not in conceptuses recovered after day 15 of pregnancy. IL-1 beta biological activity was demonstrated in days 11 and 12 conceptus homogenates, but not in homogenates of days 112 allantochorion. Low levels of IL-1 beta mRNA were detected by Northern blot analysis in Day 15 conceptuses, endometrium and myometrium only when poly(A+) RNA was used. The production of IL-1 beta by peri-implantation pig conceptuses was temporally associated with maternal recognition of pregnancy. The results suggest that conceptus IL-1 beta may be important for conceptus development and establishment of pregnancy.