The placenta of the pig. II. The ultrastructure of the areolae

Morphology and Immunoexpression of Selenoproteins in Term Placenta of Alpaca (Vicugna pacos) from the Peruvian Andes

South American camelids inhabit high-altitude environments characterized by hypoxia, influencing embryonic, fetal, and placental development. This study examined the term placenta morphology of alpacas (Vicugna pacos, N = 12) and the immunoexpression of antioxidant selenoproteins (SP). We hypothesize that the placenta of alpacas, adapted to high altitudes, has characteristics with other species also adapted to altitude. Placentas were paraffin-embedded, sectioned (3-5 µm), stained with hematoxylin-eosin (H&E), Masson's trichrome, and picrosirius red, and analyzed via light and polarized light microscopy. The chorion showed simple cuboidal epithelium with binucleated cells, a subepithelial mesenchyme rich in blood capillaries (area: 124.90 ± 9.82 µm2), and type III collagen fibers. The chorionic villi measured 2740.22 ± 132.75 µm. The allantois contained a simple columnar epithelium and mesenchyme with type I collagen fibers. Immunohistochemistry localized SP-N, SP-P, Dio-3, and GPx-3 in the blood capillaries and mesenchymal tissue of the chorion but not in the allantois. These findings were compared to human and sheep placentas from different altitudes due to a lack of camelid data at low levels. The morphological features resembled adaptations to hypoxia observed in other species. This preliminary study suggests a potential role for selenoproteins in hypoxia adaptation, providing a basis for future functional studies.

The Research Progress of DNA Methylation in the Development and Function of the Porcine Placenta

The pig is the most widely consumed domestic animal in China, providing over half of the meat supply in food markets. For livestock, a key economic trait is the reproductive performance, which is significantly influenced by placental development. The placenta, a temporary fetal organ, is crucial for establishing maternal-fetal communication and supporting fetal growth throughout pregnancy. DNA methylation is an epigenetic modification that can regulate the gene expression by recruiting proteins involved in gene silencing or preventing transcription factor binding. To enhance our understanding of the molecular mechanisms underlying DNA methylation in porcine placental development, this review summarizes the structure and function of the porcine placenta and the role of DNA methylation in placental development.

Relevance of the regulation of the brain-placental axis to the nocturnal bottleneck of mammals

INTRODUCTION

Evolutionary theory suggests that the ancestors of all placental animals were nocturnal. Visual perceptive function of mammalian brain has evolved extensively, but nearly 70 % of today's mammals are still nocturnal. While placental influence on brain development is known, if placenta plays a role in the visual perceptive function of mammalian brain remains untested. The present study aims to test this hypothesis.

METHODS

In this study, single-nuclei RNA sequencing was performed to identify genes expressed in the pig placenta and fetal brain, and then compared with the orthologous genes expressed in the placenta and fetal brain cells of mouse. Differential gene expression analysis was performed to identify placental genes regulated differentially between nocturnal and diurnal animals. Phylogenetic modeling was performed to test correlated evolution between placenta type, and the nocturnal or diurnal activity among different mammals.

RESULTS

The results showed that genes differentially regulated in the fetal brain were related to visual perception whereas the placental genes were related to the nocturnal or diurnal activity in placental animals. Phylogenetic modeling of these genes in thirty-four diverse mammalian species showed evidence for evolutionary link between placenta and the nocturnal/diurnal activity in animals.

DISCUSSION

The findings of this study suggest that the placenta plays a role in the evolution of visual perceptive function of brain to shape the nocturnal or diurnal activity of placental animals.

Localization of peptide hormones in the placentas of Bryde's (Balaenoptera brydei), sei (B. borealis), and common minke (B. acutorostrata) whales

In this study, we examined the morphological features of the placentas from 3 species of rorqual whales (Balaenopteridae), namely Bryde's (Balaenoptera brydei), sei (B. borealis), and common minke (B. acutorostrata) whales, and verified the secretion of 2 placental-specific peptide hormones, placental lactogen (PL) and chorionic gonadotropin (CG). The placentas were collected in the second phase of the Japanese Whale Research Program under a special permit in the North Pacific (JARPN II) between 2009 and 2010. For all three species of rorqual whales, as the fetus grew, the interdigitation between the maternal endometrial folds and chorionic villi became more complicated, and many blood capillaries of chorionic villi and endometrium became larger and infiltrated the trophoblast cells and endometrial epithelial cells, respectively. In the immunohistochemical examination, the trophoblast cells (except for areolar trophoblast cells) showed immunoreactivities for the PL and luteinizing hormone (LH) antibodies, and this phenomenon was similar in the placentas of all 3 rorqual whale species. Our results suggest that PL and LH-like CG play roles in regulating pregnancy in the placenta of cetacean.

Insights into the Regulation of Implantation and Placentation in Humans, Rodents, Sheep, and Pigs

Precise cell-specific spatio-temporal molecular signaling cascades regulate the establishment and maintenance of pregnancy. Importantly, the mechanisms regulating uterine receptivity, conceptus apposition and adhesion to the uterine luminal epithelia/superficial glandular epithelia and, in some species, invasion into the endometrial stroma and decidualization of stromal cells, are critical prerequisite events for placentation which is essential for the appropriate regulation of feto-placental growth for the remainder of pregnancy. Dysregulation of these signaling cascades during this critical stage of pregnancy can lead to pregnancy loss, impaired growth and development of the conceptus, and alterations in the transplacental exchange of gasses and nutrients. While many of these processes are conserved across species, significant variations in the molecular mechanisms governing maternal recognition of pregnancy, conceptus implantation, and placentation exist. This review addresses the complexity of key mechanisms that are critical for the establishment and maintenance of a successful pregnancy in humans, rodents, sheep, and pigs. Improving understanding of the molecular mechanisms governing these processes is critical to enhancing the fertility and reproductive health of humans and livestock species.

Decreased tight junction protein intensity in the placenta of porcine reproductive and respiratory syndrome virus-2 infected fetuses

INTRODUCTION

Existing strategies to control porcine reproductive and respiratory syndrome (PRRS) are not completely effective and require alternative approaches. Although intrauterine growth restricted (IUGR) fetuses are more resilient to transplacental PRRS virus-2 (PRRSV2) infection compared to normal fetuses, the exact mechanisms are unknown. The objective of this research was to assess abundance and localization of a subset of tight junction (TJ) proteins in the maternal-fetal interface and any alterations that may affect the movement of nutrients or PRRSV2 across the epitheliochorial placenta.

METHODS

Paraffin-embedded samples of placenta from non-infected control (CTRL) and PRRSV2 infected fetuses (IUGR, non(N)-IUGR, meconium-stained (MEC) (n = 6 per group) were randomly selected from a large challenge trial and immunostained for claudins (CLDN) 1, 3, 4, 7 and tight junction protein 1 (TJP1). Immunostaining intensity was semi-subjectively scored by region.

RESULTS

Intensity of CLDN1 was lower in placenta of IUGR, MEC, and N-IUGR fetuses compared to CTRL, mainly in fetal epithelium and maternal endothelial cells (MECL). CLDN4 intensity was lower in MECL of IUGR compared to CTRL and MEC fetuses. TJP1 intensity was lower in maternal and fetal epithelia of placenta within IUGR, MEC, and N-IUGR fetuses versus CTRL.

DISCUSSION

Differences were mainly observed between PRRSV2 infected and non-infected groups indicating TJ integrity was affected by PRRSV2 infection. These results provide insights into the potential mechanisms of transplacental transmission of PRRSV2; however, since only CLDN4 differed amongst the infected groups, PRRSV2 induced changes in TJ integrity do not appear to explain variation in fetal outcomes after infection.

[Assessment of immunogenic activity of the cloned human rotavirus A WA strain.]

INTRODUCTION

Rotovirus infection (RVI) caused by the dsRNA-containing virus from genus Rotavirus, Reoviridae family, belonging to group A (RVA), is the cause of severe diarrhea in human and other mammalian species. Vaccination is the most effective way to reduce the incidence of RVI. At present, the effectiveness of using gnotobiotic piglets as a universal model for reproducing human rotavirus infection and assessing the quality of RVI vaccine preparations has been experimentally proven.

OBJECTIVES

Evaluation of immunogenic activity of the cloned RVA Wa strain in the new-born Vietnamese potbellied piglets trial.

MATERIAL AND METHODS

Development of viral preparations of the cloned human Wa strain PBA, development of human RVA rVP6, ELISA, polymerase chain reaction with reverse transcription, immunization and experimental infection of newborn piglets.

RESULTS

The article presents the results of the experiment on double immunization of newborn piglets with native virus preparations with the infection activity 5.5 lg TCID₅₀/ml, 3 cm³ per dose, HRV with adjuvant 500 µg per dose and mock preparation (control group) followed with experimental inoculation of all animals with virulent virus strain Wa G1P[8] human RVA with infectious activity of 5.5 lg TCID₅₀/ml in 5 cm³ dose. Development of clinical signs of disease and animal death were observed only in control group. RT-PCR system to detect RVA RNA in rectal swabs, samples of small intestine and peripheral lymph nodes was developed. ELISA based on obtained human RVA rVP6 was developed and results on RVA-specific IgG-antibodies in serum samples of experimental piglets are presented.

CONCLUSION

In the course of the research, a high immunogenic activity of the native and purified virus of the cloned Wa RVA strain Wa was established and the possibility of its use as the main component of the RVI vaccine was confirmed. The possibility of using conventional newborn pigs instead of gnotobiotic piglets as an experimental model was demonstrated.

Breed differences in placental development during late gestation between Chinese Meishan and White crossbred gilts in response to intrauterine crowding

The objective of this study was to evaluate placental development during late gestation (day 100) between Chinese Meishan (CM; n = 7) and White crossbred (WC; n = 5) gilts following intrauterine crowding induced by unilaterally hysterectomy-ovariectomy. Gross placental morphology and areolae density as well as histological morphology (i.e., folded bilayer and placental stroma) were analyzed using computer-assisted morphometry for placentas of the smallest and largest fetuses within each litter. There was a breed by fetal size interaction (P <  0.01) for areolae density in which placentas for large CM fetuses had greater areolae density compared to small CM fetuses, but the density of areolae was greater for CM fetuses compared to WC fetuses, irrespective of fetal size. The width of the folded bilayer was greater (P <  0.01) in placentas for WC gilts compared to CM gilts, irrespective of fetal size. Placentas for small fetuses had greater (P <  0.01) folded bilayer width compared to large fetuses, irrespective of breed. The placental stromal width was greater (P < 0.01) in placentas for large fetuses compared to small, irrespective of breed. The difference between stromal width in placentas between divergent-sized littermates, however, was greater (P =  0.05) in WC gilts compared to CM gilts, indicating there was a limited response to intrauterine crowding in CM gilts. These results indicate there is an altered placental development during late gestation in CM compared to WC gilts, thus, there are likely different mechanisms for responding to intrauterine crowding between breeds.

The Early Stages of Implantation and Placentation in the Pig

Pregnancy in pigs includes the events of conceptus (embryo/fetus and placental membranes) elongation, implantation, and placentation. Placentation in pigs is defined microscopically as epitheliochorial and macroscopically as diffuse. In general, placentation can be defined as the juxtapositioning of the endometrial/uterine microvasculature to the chorioallantoic/placental microvasculature to facilitate the transport of nutrients from the mother to the fetus to support fetal development and growth. Establishment of epitheliochorial placentation in the pig is achieved by: (1) the secretions of uterine glands prior to conceptus attachment to the uterus; (2) the development of extensive folding of the uterine-placental interface to maximize the surface area for movement of nutrients across this surface; (3) increased angiogenesis of the vasculature that delivers both uterine and placental blood and, with it, nutrients to this interface; (4) the minimization of connective tissue that lies between these blood vessels and the uterine and placental epithelia; (5) interdigitation of microvilli between the uterine and placental epithelia; and (6) the secretions of the uterine glands, called histotroph, that accumulate in areolae for transport though the placenta to the fetus. Placentation in pigs is not achieved by invasive growth of the placenta into the uterus. In this chapter, we summarize current knowledge about the major events that occur during the early stages of implantation and placentation in the pig. We will focus on the microanatomy of porcine placentation that builds off the excellent histological work of Amoroso and others and provide a brief review of some of the key physiological, cellular, and molecular events that accompany the development of "implantation" in pigs.

Steroids Regulate SLC2A1 and SLC2A3 to Deliver Glucose Into Trophectoderm for Metabolism via Glycolysis

The conceptuses (embryo/fetus and placental membranes) of pigs require energy to support elongation and implantation, and amounts of glucose and fructose increase in the uterine lumen during the peri-implantation period. Conceptuses from day 16 of pregnancy were incubated with either 14C-glucose or 14C-fructose and amounts of radiolabeled CO2 released from the conceptuses measured to determine rates of oxidation of glucose and fructose. Glucose and fructose both transport into conceptuses, and glucose is preferentially metabolized in the presence of fructose, whereas fructose is actively metabolized in the absence of glucose and to a lesser extent in the presence of glucose. Endometrial and placental expression of glucose transporters SLC2A1, SLC2A2, SCL2A3, and SLC2A4 were determined. SLC2A1 messenger RNA (mRNA) and protein, and SLC2A4 mRNA were abundant in the uterine luminal epithelium of pregnant compared to cycling gilts, and increased in response to progesterone and conceptus-secreted estrogen. SLC2A2 mRNA was expressed weakly by conceptus trophectoderm on day 15 of pregnancy, whereas SLC2A3 mRNA was abundant in trophectoderm/chorion throughout pregnancy. Therefore, glucose can be transported into the uterine lumen by SLC2A1, and then into conceptuses by SLC2A3. On day 60 of gestation, the cell-specific expression of these transporters was more complex, suggesting that glucose and fructose transporters are precisely regulated in a spatial-temporal pattern along the uterine-placental interface of pigs to maximize hexose sugar transport to the pig conceptus/placenta.

EVALUATION OF THE MOLECULAR-BIOLOGICAL PROPERTIES OF HUMAN ROTAVIRUS A STRAIN WA

Introduction. Rоtaviruses are amоng the leading causes of severe diarrhea in children all over the Wоrld. Vaccination is considered to be the mоst effective way to cоntrоl the disease. Currently available vaccines for prevention of rоtavirus infection are based on live attenuated rotavirus strains human оr animal origin. Objectives and purposes. The aim of this investigation was to study the biological and genetic properties of an actual epidemic human rotavirus A (RVA) strain Wa G1P[8] genotype. Material and methods. RVA Wa reproduction in a monolayer continuous cell lines, purification and concentration of RVA antigen, PAAG electrophoresis and Western-Blot, electrophoresis of viral genomic RNA segments, sequencing. Results. Human RVA G1P[8] Wa strain biological and molecular genetic properties were assessed in the process of the adaptation to MARC145 continuous cell line. Cell cultured RVA antigen was purified, concentrated and then characterized by the method of PAAG electrophoresis and immunoblot. To verify RVA Wa genome identity, electrophoresis of viral genomic RNA segments was performed. The lack of accumulation of changes in the RVA Wa genome during adaptation to various cell cultures and during serial passages was demonstrated by sequencing fragments of the viral genome. Conclusion. RVA Wa strain is stable, it possesses high biological activity: it has been successfully adapted to the MARC145 cell line and RVA Wa virus titer after the adaptation reached 7,5-7,7 lg TCID50/ml. The identity of the cultivated RVA to the original strain Wa G1P[8] was confirmed.

Development and Function of Uterine Glands in Domestic Animals

All mammalian uteri contain glands that synthesize or transport and secrete substances into the uterine lumen. Uterine gland development, or adenogenesis, is uniquely a postnatal event in sheep and pigs and involves differentiation of glandular epithelium from luminal epithelium, followed by invagination and coiling morphogenesis throughout the stroma. Intrinsic transcription factors and extrinsic factors from the ovary and pituitary as well as the mammary gland (lactocrine) regulate uterine adenogenesis. Recurrent pregnancy loss is observed in the ovine uterine gland knockout sheep, providing unequivocal evidence that glands and their products are essential for fertility. Uterine gland hyperplasia and hypertrophy during pregnancy are controlled by sequential actions of hormones from the ovary and/or pituitary as well as the placenta. Gland-derived histotroph is transported by placental areolae for fetal growth. Increased knowledge of uterine gland biology is expected to improve pregnancy outcomes, as well as the health and productivity of mothers and their offspring.

Interactions between human microbiome, diet, enteric viruses and immune system: Novel insights from gnotobiotic pig research

Studies over the past few decades demonstrated that gnotobiotic (Gn) pigs provide an unprecedented translational model to study human intestinal health and diseases. Due to the high degree of anatomical, physiological, metabolic, immunological, and developmental similarity, the domestic pig closely mimics the human intestinal microenvironment. Also, Gn piglets can be efficiently transplanted with human microbiota from infants, children and adults with resultant microbial profiles remarkably similar to the original human samples, a feat consistently not achievable in rodent models. Finally, Gn and human microbiota-associated (HMA) piglets are susceptible to human enteric viral pathogens (including human rotavirus, HRV) and can be fed authentic human diets, which further increases the translational potential of these models. In this review, we will focus on recent studies that evaluated the pathophysiology of protein malnutrition and the associated dysbiosis and immunological dysfunction in neonatal HMA piglets. Additionally, we will discuss studies of potential dietary interventions that moderate the effects of malnutrition and dysbiosis on antiviral immunity and HRV vaccines in HMA pigs. Such studies provide novel models and novel mechanistic insights critical for development of drug interventions.

Expression of progesterone receptor in the porcine uterus and placenta throughout gestation: correlation with expression of uteroferrin and osteopontin

Progesterone (P4) stimulates production and secretion of histotroph, a mixture of hormones, growth factors, nutrients, and other substances required for growth and development of the conceptus (embryo or fetus and placental membranes). Progesterone acts through the progesterone receptor (PGR); however, there is a gap in our understanding of P4 during pregnancy because PGR have not been localized in the uteri and placentae of pigs beyond day 18. Therefore, we determined endometrial expression of PGR messenger RNA (mRNA) and localized PGR protein in uterine and placental tissues throughout the estrous cycle and through day 85 of pregnancy in pigs. Further, 2 components of histotroph, tartrate-resistant acid phosphatase 5 (ACP5; uteroferrin) and secreted phosphoprotein 1 (SPP1; osteopontin) proteins, were localized in relation to PGR during pregnancy. Endometrial expression of PGR mRNA was highest at day 5 of the estrous cycle, decreased between days 5 and 11 of both the estrous cycle and pregnancy, and then increased between days 11 and 17 of the estrous cycle (P < 0.01), but decreased from days 13 to 40 of pregnancy (P < 0.01). Progesterone receptor protein localized to uterine stroma and myometrium throughout all days of the estrous cycle and pregnancy. PGR were expressed by uterine luminal epithelium (LE) between days 5 and 11 of the estrous cycle and pregnancy, then PGR became undetectable in LE through day 85 of pregnancy. During the estrous cycle, PGR were downregulated in LE between days 11 and 15, but expression returned to LE on day 17. All uterine glandular epithelial (GE) cells expressed PGR from days 5 to 11 of the estrous cycle and pregnancy, but expression decreased in the superficial GE by day 12. Expression of PGR in GE continued to decrease between days 25 and 85 of pregnancy; however, a few glands near the myometrium and in close proximity to areolae maintained expression of PGR protein. Acid phosphatase 5 protein was detected in the GE from days 12 to 85 of gestation and in areolae. Secreted phosphoprotein 1 protein was detected in uterine LE in apposition to interareolar, but not areolar areas of the chorioallantois on all days examined, and in uterine GE between days 35 and 85 of gestation. Interestingly, uterine GE cells adjacent to areolae expressed PGR, but not ACP5 or SPP1, suggesting these are excretory ducts involved in the passage, but not secretion, of histotroph into the areolar lumen and highlighting that P4 does not stimulate histotroph production in epithelial cells that express PGR.

Relationships of CD163 and CD169 positive cell numbers in the endometrium and fetal placenta with type 2 PRRSV RNA concentration in fetal thymus

Several routes of porcine reproductive and respiratory virus PRRSV transmission across the porcine diffuse epitheliochorial placentation have been proposed, but none have been proven. The objectives of this study were to investigate associations between numbers of CD163 and CD169 positive macrophages, cathepsin positive areolae, and type 2 PRRSV load at the maternal-fetal interface in order to examine important factors related to transplacental infection. On gestation day 85 ± 1, naïve pregnant gilts were inoculated with PRRSV (n = 114) or were sham inoculated (n = 19). At 21 days post-inoculation (dpi), dams and their litters were humanely euthanized and necropsied. Samples of the maternal-fetal interface (uterus with fully attached placenta) and fetal thymus were collected for analysis by RT-qPCR to quantify PRRSV RNA concentration. The corresponding paraffin-embedded uterine tissue sections were subjected to immunohistochemistry for PRRSV nucleocapsid N protein, CD163, CD169, and cathepsin. Our findings confirm significant increases in the numbers of PRRSV, CD163 and CD169 positive cells at the maternal-fetal interface during type 2 PRRSV infection in pregnant gilts. PRRSV load in fetal thymus was positively related to CD163(+) cell count in endometrium and negatively related to CD163(+) cell count in placenta, but unrelated to CD169 counts or cathepsin positive areolae. The endometrium:placenta ratio of CD163 cells, and to a lesser extent CD169 cells, was significantly associated with an increase fetal viral load in thymus. These findings suggest a more important role for CD163(+) cells following trans-placental PRRSV infection, but dichotomous responses in endometrium and placenta for both CD163 and CD169 cells.

The evolution of the placenta

The very apt definition of a placenta is coined by Mossman, namely apposition or fusion of the fetal membranes to the uterine mucosa for physiological exchange. As such, it is a specialized organ whose purpose is to provide continuing support to the developing young. By this definition, placentas have evolved within every vertebrate class other than birds. They have evolved on multiple occasions, often within quite narrow taxonomic groups. As the placenta and the maternal system associate more intimately, such that the conceptus relies extensively on maternal support, the relationship leads to increased conflict that drives adaptive changes on both sides. The story of vertebrate placentation, therefore, is one of convergent evolution at both the macromolecular and molecular levels. In this short review, we first describe the emergence of placental-like structures in nonmammalian vertebrates and then transition to mammals themselves. We close the review by discussing the mechanisms that might have favored diversity and hence evolution of the morphology and physiology of the placentas of eutherian mammals.

Structure and functions of the placenta in common minke (Balaenoptera acutorostrata), Bryde's (B. brydei) and sei (B. borealis) whales

The structure and functions of placentas were examined in 3 species of rorqual whales, common minke (Balaenoptera acutorostrata), Bryde's (B. brydei) and sei (B. borealis) whales, with the aim of confirming the structural characteristics of the chorion, including the presence of the areolar part, and clarifying steroidogenic activities and fetomaternal interactions in the placentas of these whales. Placentas were collected from the second phase of the Japanese Whale Research Program under Special Permit in the North Pacific (JARPN II). Histological and ultrastructural examinations revealed that these whale placentas were epitheliochorial placentas with the interdigitation of chorionic villi lined by monolayer uninucleate cells (trophoblast cells) and endometrial crypts as well as folded placentation by fold-like chorionic villi. Moreover, well-developed pouch-like areolae were observed in the placentas, and active absorption was suggested in the chorionic epithelial cells of the areolar part (areolar trophoblast cells). Berlin blue staining showed the presence of ferric ions (Fe(3+)) in the uterine glandular epithelial cells and within the stroma of chorionic villi in the areolar part. An immunohistochemical examination revealed tartrate-resistant acid phosphatase (TRAP; known as uteroferrin in uteri) in the cytoplasm of glandular cells and areolar trophoblast cells. This result suggested that, in cetaceans, uteroferrin is used to supply iron to the fetus. Furthermore, immunoreactivity for P450scc and P450arom was detected in trophoblast cells, but not in areolar trophoblast cells, suggesting that trophoblast cells synthesize estrogen in whale placentas. Therefore, we herein immunohistochemically revealed the localization of aromatase and uteroferrin in cetacean placentas during pregnancy for the first time.

Environmental factors affecting pregnancy: endocrine disrupters, nutrients and metabolic pathways

Uterine adenogenesis, a unique post-natal event in mammals, is vulnerable to endocrine disruption by estrogens and progestins resulting in infertility or reduced prolificacy. The absence of uterine glands results in insufficient transport of nutrients into the uterine lumen to support conceptus development. Arginine, a component of histotroph, is substrate for production of nitric oxide, polyamines and agmatine and, with secreted phosphoprotein 1, it affects cytoskeletal organization of trophectoderm. Arginine is critical for development of the conceptus, pregnancy recognition signaling, implantation and placentation. Conceptuses of ungulates and cetaceans convert glucose to fructose which is metabolized via multiple pathways to support growth and development. However, high fructose corn syrup in soft drinks and foods may increase risks for metabolic disorders and increase insulin resistance in adults. Understanding endocrine disrupters and dietary substances, and novel pathways for nutrient metabolism during pregnancy can improve survival and growth, and prevent chronic metabolic diseases in offspring.

Areolae of the placenta in the Antarctic minke whale (Balaenoptera bonaerensis)

In this study, we examined the existence and structure of areolae and the steroidogenesis of areolar trophoblast cells in the Antarctic minke whale placenta morphologically and immunohistochemically. Placentas were collected from the 15th, 16th and 18th Japanese Whale Research Program under Special Permit in the Antarctic (JARPA) and 1st JARPA II organized by the Institute of Cetacean Research in Tokyo, Japan. The opening and cavity of fetal areolae formed by taller columnar trophoblast cells (areolar trophoblast cells) with long microvilli and a bright cytoplasm, as compared with the trophoblast cells of the chorionic villi interdigitating with the endometrial crypts, were recognized in observations of serial sections. The opening of the areolar cavity was hidden by chorionic villi with areolar trophoblast cells. Furthermore, a closed pouch-like structure lined by tall columnar cells similar to areolar trophoblast cells within the stroma of chorionic villi was noticed and continued to the areolar cavity, with the opening seen on serial sections. In a surface investigation of the chorion and endometrium by SEM, maternal (endometrial) areolae irregularly surrounded by endometrial folds were obvious. Moreover, we distinguished areolar trophoblast cells with long microvilli attached with many blebs from trophoblast cells. In our immunohistochemical observations, a steroidogenic enzyme, cytochrome P450 side chain cleavage enzyme (P450scc), was detected with strong immunoreactivity in trophoblast cells. However, areolar trophoblast cells showed weak or no immunoreactivity for P450scc.

Evolutionary transformations of fetal membrane characters in Eutheria with special reference to Afrotheria

Analysis of molecular data sets has provided new insights into higher-level relationships of living Eutheria, including the recognition of Afrotheria as a novel taxon. This offers an opportunity to take a fresh look at the evolution of organ systems, including some that are little used in traditional systematics. In the present study, we attempted a reconstruction of the evolution of characters associated with placentation, the fetal membranes and the female reproductive tract. The evolutionary history of 21 characters has been traced, based on a current hypothesis of eutherian relationships, by applying the computer program MacClade. Accordingly, the analysis provides a first comprehensive interpretation of the stem species pattern of Eutheria. Of particular note, this pattern includes an endotheliochorial chorioallantoic placenta. The reconstructed pattern of Eutheria does not change in the basal nodes of the group. Thus, no character transformations occur on the stem lineages of Laurasiatheria or Euarchontoglires, and even Afrotheria has mostly plesiomorphic character conditions. However, two character transformations occur on the common stem lineage of Afrotheria and its sister taxon Xenarthra, i.e., amniogenesis by cavitation instead of folding and the precocial state of the newborn. In addition, we recognized one character transformation on the stem lineage of Afrotheria, i.e., the occurrence of a four-lobed allantoic sac. Thus, contrary to previous assertions, it is possible to identify morphological characters that could be synapomorphic for this novel taxon.

Development of the Areola in the Early Placenta of the One-humped Camel (Camelus dromedarius): A Light, Scanning and Transmission Electron Microscopical Study

This study aimed to elucidate development of the areola in the early dromedary placenta in comparison with that of the pig and mare. Placental tissues from 25 pregnant camels were obtained from Cairo abattoir and prepared for light, scanning and transmission electron microscopy by routine methods. Vascular casts were made by injection of 4 : 1 liquid plastic mixture of mercox and methylmethacrylate. Areolar formation was first observed at 4.5 cm curved-crown-rump CVR length, while by 5-9 cm CVR length, the endometrial surface was uneven and studded with numerous uterine gland openings, where corresponding foetal areolae were barely detectable and the foetal areolar cells were of variable appearance and covered with long microvilli. At 10-13 cm CVR length the uterine gland openings developed irregular folds and the maternal areolar cells showed numerous apical blebs. At 14-29 cm CVR length the foetal areolae showed a great increase in height at the expense of their width. At 30-34 cm (CVR) length the maternal areolae appeared discoid and sharply demarcated from the surrounding inter-areolar tissues and the foetal areolae were rounded to irregular in shape with well-developed areolar rims. The vascular casts showed a widely meshed capillary network on the maternal areola, connecting with the pre- and post-capillary vessels, whereas the foetal side showed a relatively dense capillary meshwork. These studies indicate that the areola in the placenta of the one-humped camel is of the regular type like in the pig, and is poorly vascularized.

Ultrastructure of the placentae of the natricine snake, Virginia striatula (Reptilia: Squamata)

Virginia striatula is a viviparous snake with a complex pattern of embryonic nutrition. Nutrients for embryonic development are provided by large, yolked eggs, supplemented by placental transfer. Placentation in this species is surprisingly elaborate for a predominantly lecithotrophic squamate reptile. The embryonic-maternal interface consists of three structurally distinct areas, an omphalallantoic placenta and a regionally diversified chorioallantoic placenta. The chorioallantoic placenta over the embryonic hemisphere (paramesometrial region) of the egg, features close apposition of embryonic and uterine blood vessels because of the attenuate form of the interceding epithelial cells. The periphery of the chorioallantoic placenta, which is adjacent to the omphalallantoic placenta, is characterized by a simple cuboidal uterine epithelium apposed to a stratified cuboidal chorionic epithelium. There are no sites with attenuate epithelial cells and close vascular apposition. The morphology of the omphalallantoic placenta is similar to that of the peripheral chorioallantoic placenta, except that the height of uterine epithelial cells is greater and allantoic blood vessels are not associated with the embryonic epithelium. The functional capabilities of the three placental regions are not known, but structural characteristics suggest that the omphalallantoic placenta and peripheral zone of the chorioallantoic placenta are sites of nutritional provision via histotrophy. The paramesometrial region of the chorioallantoic placenta is also nutritive, in addition to functioning as the primary embryonic respiratory system. The structure of the chorioallantoic placenta of V. striatula is a new placental morphotype for squamate reptiles that is not represented by a classic model for the evolution of reptilian placentation.

Temporal and spatial expression of connective tissue growth factor (CCN2; CTGF) and transforming growth factor beta type 1 (TGF-beta1) at the utero-placental interface during early pregnancy in the pig

AIMS

To determine the localisation and distribution of connective tissue growth factor (CCN2; CTGF) and transforming growth factor beta type 1 (TGF-beta1) in uterine tissues from cycling and early pregnant pigs.

METHODS

In situ hybridisation and immunohistochemistry were used to localise CCN2 (CTGF) or TGF-beta1 in uteri obtained from gilts on days 0, 5, 10, 12, 15, and 18 of the oestrous cycle or days 10, 12, 14, 16, 17, and 21 of gestation.

RESULTS

In cycling animals, CCN2 (CTGF) mRNA and protein were abundant in luminal epithelial cells (LECs) and glandular epithelial cells (GECs), with lesser amounts in stromal fibroblasts and little or none in endothelial cells. A similar pattern of staining was seen up to day 10 of pregnancy, except that overall staining intensities for CCN2 (CTGF) mRNA or protein were higher and that stromal and endothelial cells were CCN2 (CTGF) positive. However, on days 12-17 there was a striking decrease in the amount of CCN2 (CTGF) in LECs at the utero-conceptus interface, which was associated with maternal stromal matrix reorganisation and the onset of subepithelial neovascularisation. This differential distribution of CCN2 (CTGF) was localised to those LECs that were in close proximity to or in apposition with trophoblast cells. This decrease in CCN2 (CTGF) staining was transient in nature and high amounts of CCN2 (CTGF) were again apparent in LECs on days 17-21, when endometrial neovascularisation and matrix remodelling were complete. The expression of uterine TGF-beta1 was comparable to that of CCN2 (CTGF) at most stages of the oestrous cycle or early pregnancy. Pre-elongation blastocysts recovered on day 10 were positive for both CCN2 (CTGF) and TGF-beta1 in the extra-embryonic trophectoderm, endoderm, and inner cell mass. On day 12, trophectoderm expressed low amounts of TGF-beta1 mRNA and non-detectable amounts of TGF-beta1 protein or CCN2 (CTGF) mRNA or protein. By days 17-21, the expression of both growth factors in the extra-embyronic/placental membranes increased and frequently exceeded that seen in LECs.

CONCLUSIONS

The pattern of CCN2 (CTGF) production during the initial attachment phase supports a role for this factor in stromal remodelling and neovascularisation, although alternative functions at later stages such as epithelial-epithelial interactions are also possible. In most major cell types in the uterus or utero-placental unit, CCN2 (CTGF) expression was highly correlated with that of TGF-beta(1), indicating that CCN2 (CTGF) may mediate some of the functions of TGF-beta in the reproductive tract during the oestrous cycle and pregnancy. The data further highlight epithelium as an important source of CCN2 (CTGF) in the regulation of uterine function.

Piglet and placental traits at term in relation to the estrogen receptor genotype in gilts

Liveborn piglets from gilts with estrogen receptor (ESR) genotype AA (95 AA-AA and 91 AA-AB piglets), AB (88 AB-AA, 118 AB-AB, and 37 AB-BB piglets), and BB (97 BB-AB and 89 BB-BB piglets) were compared after farrowing, to examine whether piglet ESR genotype (ESRp) nested within maternal ESR genotype (ESRm) affected placental traits at term, piglet birth weight, and growth until weaning. Furthermore, the relation of birth weight to various placental traits and the relations between placental traits were evaluated relative to ESR genotype. For this study, 62 Large White x Meishan F2 crossbred gilts (18 AA, 24 AB, and 20 BB) were used. The gilts belonged to a population in which the A allele is favorable for litter size. ESRp nested within ESRm did not affect placental length, weight, surface area and number of areolae. ESRp nested within ESRm affected amnion weight (AA-AA amnions were heavier than AA-AB, AB-AA and BB-AB amnions), placental weight after including placental surface area in the model (AA-AB placentae were lighter than AA-AA, AB-BB and BB-AB placentae), placental efficiency calculated as birth weight divided by placental weight (AB-AA placentae were less efficient than AA-AB placentae), and the relations of birth weight to placental weight and birth weight to number of areolae. The found differences imply an interaction of maternal and fetal ESR genotype on placental traits (especially weight and number of areolae) during fetal development. Furthermore, the found effects on placental and amnion weight might be the result of a difference in thickness or vascularization or both. The favorable ESR allele for litter size, i.e. the A allele, appears to be the unfavorable allele for pre-weaning piglet growth. Therefore, further research on ESR in relation to vascularization, weight and thickness of placentae. uterine size, endometrial gland development, and piglet growth is recommended.

The effect of estrogen receptor genotype on litter size and placental traits at term in F2 crossbred gilts

The effect of estrogen receptor (ESR) genotype (two alleles, A and B) on litter size of 275 Large White x Meishan F2 crossbred gilts (73 AA, 126 AB and 76 BB gilts) was tested. In addition, for 63 of these gilts (18 AA, 24 AB, and 21 BB) the effect of ESR genotype on average placental traits at term was tested, since individual placental information was available for 88% of the 628 liveborn piglets. Without affecting average birth weight of the piglets, ESR genotype significantly affected litter size, i.e. AB gilts had larger litters than BB gilts (P < 0.05). Total number born was 11.38+/-0.38, 11.88+/-0.28, and 10.68+/-0.35, while number born alive was 10.45+/-0.39, 11.07+/-0.29, and 9.85+/-0.36 for AA, AB and BB gilts, respectively. Since the B allele in previous research was associated with largest litters, the hypothesis that ESR is a marker rather than the major gene itself is discussed. Average placental length, surface area, and weight including and excluding amnion were not affected by ESR genotype. However, placentae of AB gilts had a significantly lower number of areolae per placenta than BB gilts and had a lower number of areolae/cm2 placenta than AA and BB gilts. Number of areolae was 8945+/-663, 7240+/-619, and 9694+/-633, for AA, AB and BB gilts, respectively. Although the reason for the low number of areolae on placentae in AB gilts is not yet known, the results suggest that the ESR linked major gene for litter size might be involved in the development and activity of endometrial glands.

Initial vascularisation in the pig placenta: II. Demonstration of gland and areola-gland subunits by histology and corrosion casts

Tissues from 10 pregnant pigs between 9 1/2 and 43 days post coitum (p.c.) were prepared for histology and vascular corrosion casts to examine the vascularisation of the gland and areola-gland subunits of the early pig placenta. The endometrial vascular networks shown by casts were equal in both glandular and interglandular fields from days 9 1/2 to 14-15 p.c. This represents a cyclic stage uninfluenced by the early implanting embryo on day 13 p.c. By day 15 p.c., the first areola formation was observed both histologically and on casts. The maternal areolar and glandular capillary network developed into a widely meshed loose type, in contrast to the interareolar type which had a dense and parallel architecture. In some cases extremely large, crooked, and highly anastomosed maternal capillaries developed between these two networks. This specialized transition is thought to form the base for the ring-like seal formation (RSF) of the areolar periphery. A firm materno-fetal anchor therefore "seals" the areola and its glandular secretory contents from its interareolar surroundings. Therefore, the glandular and maternal areolar vasculatures are clearly discernable from that of the fetal areolar vasculature. The former are associated with the known maternao-fetal substance transfer of the porcine areolar-gland subunit. This association, however, seems to remain unspecialized in early placentation, as only the regular roundish areola--not the irregular areola--can be distinctly detected.

Development and structure of the placenta and fetal membranes of nonhuman primates

This survey examines placental and fetal membrane structure, function, and development in nonhuman primates. It will focus on these aspects of fetal membranes in species exemplifying the two main types of primate placentation. The chorioallantoic placentas of most strepsirhine primates (e.g., lorises and lemurs), are diffuse, villous and epitheliochorial in structure. Villi are stout, usually unbranched and interdigitate with indentations in the uterine lining. Early in gestation trophoblast cells are columnar but with advancing gestational age considerable thinning of the interhemal membrane occurs. The villous tips have indented regions that appear to be involved in absorption of histotroph. Accessory placental structures known as areolae or chorionic vesicles occur in many strepsirhines. These are cup-shaped specializations that develop opposite the mouths of uterine glands and appear active in absorption of glandular secretions. In addition, most strepsirhines are characterized by a large yolk sac early in gestation, a transient choriovitelline placenta, and most have a large allantoic sac. In strepsirhines, amniogenesis occurs by folding. In contrast, the chorioallantoic placentas of most haplorhines are discoidal, villous, and hemochorial. The species emphasized in the review are macaque monkeys. The placental villi are covered by a layer of syncytiotrophoblast; the latter is active in maternal-fetal transport and hormone synthesis. In some haplorhines, extravillous trophoblast invades deeply into the endometrium and also into spiral arteries supplying the placenta. Other fetal membranes include 1) nonvillous chorion (chorion laeve); there is evidence supporting both an absorptive and synthetic role for trophoblast of the chorion laeve; 2) yolk sac, which is unusual in that a secondary yolk sac is formed. The yolk sac has both synthetic and absorptive functions in early gestation; and 3) amnion; amniogenesis in haplorhines occurs by cavitation.

Microscopic examination of porcine conceptus-maternal interface between days 10 and 19 of pregnancy

Conceptus-maternal interactions in the pig were examined at days 10, 13, 16, and 19 of pregnancy. Contact between the chorion and uterine epithelium was not preserved on day 10, but extensive contact occurred in 3 of 5 pregnant gilts on day 13 and was related to localized differentiation of the uterine epithelium. Attachment events occurred earlier and more rapidly than previously reported, commencing in the region of the embryonic disc and progressing toward the extremities of the chorionic vesicle, with stages from apposition through attachment occurring simultaneously along a conceptus at day 13 and thereafter. Apical protuberances on maternal epithelial cells and interposing blunt chorionic processes were evident at sites of early maternal-conceptus interaction, but were reduced at regions exhibiting microvillous interdigitation. Placentation in the pig represents a developmental process consisting of a continuum of sequential events which occur over a broad time frame rather than at specific discrete times.

Hormonal control and function of secretory proteins

The uterus of the pig secretes large amounts of protein in response to progesterone. Estrogen alone has little effect but in combination with progesterone is synergistic at low doses and inhibitory at high doses. The responses of the uterus to progesterone require prolonged hormone treatment and are not immediate. The proteins secreted by the uterus of all species are believed to play some role in the nutritional and developmental support of the conceptuses, particularly during early pregnancy. Such a role is likely to be of greater importance in species such as the pig which possesses a noninvasive, diffuse-type of epitheliochorial placentation. A group of basic polypeptides dominates the uterine secretions of the pig. The best characterized is uteroferrin, a purple colored, iron-containing acid phosphatase which transports iron across the placenta. Three polypeptides which are found associated noncovalently with uteroferrin have been shown to be antigenically closely related to each other and to have arisen from a single precursor polypeptide. Their function is unknown. A family of plasmin/trypsin inhibitors which show sequence homology with bovine pancreatic trypsin inhibitor (aprotinin) has been well characterized and appears to control intrauterine proteolytic events initiated by the conceptuses. Several other proteins secreted in response to progesterone remain to be characterized and functionally defined.

Surface exchange area of the porcine placenta: morphometry of anisotropic interdigitating microvilli

The pig has a diffuse epitheliochorial placenta. The foeto-maternal surface area (Sv(F), Sv(M)) is enlarged at three levels: level I: macroscopic folds of uterine mucosa covered by foetal membranes; level II: light microscopic folds of uterine epithelium covered by trophoblastic epithelium; level III: ultrastructural formation of both maternal and foetal microvilli in an interdigitating pattern. This study presents a morphometric method, using intersection counting, to estimate the surface area of these interdigitating, highly oriented microvilli at level III, i.e. the 'true' surface exchange area. The method is applied to different stages in pregnancy. The epithelial surfaces are enlarged by a factor 8-11 due to the formation of microvilli. This factor varies during pregnancy, being lower early in gestation and before delivery, and for the first time it is shown to be significantly different for mother and foetus. At level III the foetal surface of placenta is larger than the maternal indicating that the two opposing surfaces are not congruent at the ultrastructural level and that membrane-linked placental transport may be different in mother and foetus. A three-compartment model is suggested for placental exchange with maternal, intermicrovillous and foetal compartments.

Localization of the iron transport glycoprotein, uteroferrin, in the porcine endometrium and placenta by using immunocolloidal gold

Uteroferrin, a glycoprotein implicated in transplacental iron transport in the pig, has been localized within the porcine uterus during mid pregnancy by using immunocolloidal gold labeling of sectioned material. In the endometrium where uteroferrin is synthesized, it was located exclusively in the non-ciliated cells of the glandular epithelium where it appeared to follow a common route of secretory glycoprotein from the cell (i.e., rough endoplasmic reticulum----Golgi----condensing vacuoles----secretory granules). Uteroferrin was present in the lumen of the glands and overlying placental areolae and in the large absorptive chorionic epithelial cells of the areolae. The latter cells contained numerous small vesicles and tubules as well as large endocytotic vacuoles. All these structures contained uteroferrin and are probably involved in translocating the glycoprotein in intact form from the uterine lumen to the blood capillaries draining the placenta.

An extensive lysosomal system in the maternal epithelium of the porcine placenta

The material comprised 64 placentae from 19 Danish Landrace sows representing gestational stages from 16 to 112 days. The maternal epithelium was examined by means of light and electron microscopy to describe the morphology of the irregular electron-dense bodies and membrane whorls and their relation to gestational stages. Incubation for acid phosphatase demonstrated their lysosomal nature. Electron micrographs of serial sections followed by reconstructions and freeze-fracturing demonstrated their three-dimensional structure and relation to transfer tubules. In the early stages, during the development of fetal vascularization, the maternal epithelium was dominated by inclusions of lipids and glycogen, which can easily be transferred to and utilized by the embryo. The development of an extensive lysosomal system, consisting of irregular electron-dense bodies, membrane whorls and transfer tubules, indicates that cellular digestion is an important factor in the transfer and subsequent fetal utilization of maternal nutriments in the last two-thirds of gestation, and that this development is apparently related to anatomical and physiological changes during gestation.

The fine structure of the placenta and chorionic vesicles of the bush baby, Galago crassicaudata

The fine structure of the placental villi and the chorionic vesicles of the bush baby, Galago crassicaudata, were examined. The placenta was of the diffuse epitheliochorial type. The trophoblastic epithelium of the placental villi consisted of cells joined by tight junctions and desmosomes. The apical borders of these cells interdigitated with corresponding processes on the uterine epithelial cells. The fetal capillaries indented the trophoblastic cells later in gestation, and the trophoblast over the capillaries was correspondingly thinner with advancing gestation. The trophoblast of the villi was characterized by numerous lipid droplets and moderate amounts of granular endoplasmic reticulum (ER). The apical cytoplasm often had many mitochondria as well as small electron-dense vesicles and tubules. Uterine epithelial cells contained agranular ER and a well-developed Golgi apparatus. The apical cytoplasm contained numerous granules often with an electron-dense content. The uterine epithelial cells appeared to be secretory, contributing to the electron-dense material found between the fetal and maternal cells. Fetal capillaries were of the continuous type, whereas occasional fenestrae were observed in maternal capillaries. Recesses in the trophoblastic epithelium occurred at the tips, sides, and bases of the villi. These areas had taller trophoblastic cells that appeared to be more active in phagocytosing uterine content. The chorionic vesicles are invaginations of the chorion opposite the mouths of uterine glands. A layer of columnar trophoblastic cells covered the villi of the vesicles. These cells had abundant vacuoles and coated pits and vesicles. The mesodermal component of the chorionic vesicles included a capillary network and a layer of smooth muscle cells in the wall of the vesicle. It was concluded that the trophoblast of the placental villi is engaged in both hemotrophic and histotrophic nourishment of the embryo. The specialized chorionic vesicles are particularly important in providing histotrophic nutrients to the embryo, especially the secretions of the uterine glands. The similarity of the chorionic vesicles to the areolae of other species suggests they may be the pathway by which iron is transported from mother to fetus, perhaps by receptor-mediated endocytosis of macromolecules derived from uterine gland secretions.

Uterine glands of the pig during pregnancy. An ultrastructural and cytochemical study

The ultrastructure of the porcine uterine glands is described from material taken from 11 pregnant pigs at exactly known stages of gestation (day 30; 58; 80; 100; 110). Fixation was performed by perfusion via a branch of the uterine artery and the tissue was routinely processed for electron microscopy. Additionally, cytochemical studies (phosphotungstic acid reaction for glycoproteins, according to Rambourg 1967; acid phosphatase reaction; ultrastructural localization of cellular iron, according to Parmley et al. 1978) were performed. On day 30 of pregnancy the uterine glands are coiled, simple tubular glands with a narrow lumen. The epithelial lining is simple columnar and consists basically of two cell types, ciliated cells and secretory cells. The secretory activity of the glandular epithelium is low; only a few secretory granules are present in the supranuclear cytoplasm. At midpregnancy the ultrastructure of the glands has significantly changed and the cells now show all the characteristics of high secretory activity: numerous parallel cisternae of rough endoplasmic reticulum, an extensively developed Golgi apparatus and many secretory granules which give a positive reaction for acid phosphatase and glycoproteins. The lumina of the glands are significantly enlarged and filled with a great amount of a granular, acid phosphatase-positive material. In the last third of pregnancy, only minor changes in the ultrastructure of the uterine glands are observed. The secretory activity is still high. The amount of rough endoplasmic reticulum has further increased and parallel arrays of cisternae occupy a considerable part of the supranuclear cytoplasm. The importance of the uterine secretion for embryonic nutrition and development is only partly understood. One of the secreted glycoproteins, uteroferrin, is believed to play an important role in the iron transfer from mother to fetus. From midpregnancy onward, a special cell type, the "granule laden cell" is found scattered between normal secretory cells of the uterine glands. Contrary to the opinion of Perry and Cromby (1982), we could demonstrate that these cells frequently extend to the lumen of the gland; hence the term "basal cell" seems inappropriate for this cell type.