Giant and binucleate trophoblast cells of mammals

Early Syncytialization of the Ovine Placenta Revisited

Placentation is the development of a temporary arrangement between the maternal uterus and blastocyst-derived placental tissues designed to transport nutrients, gases, and other products from the mother to the embryo and fetus. Placentation differs histologically among species, but all types of placentation share the common trait of utilizing highly complex cell-to-cell and tissue-to-tissue morphological and biochemical interactions to remodel the uterine-placental interface. An elegant series of electron microscopy (EM) images supports the classification of ovine placentation as synepitheliochorial, because uterine luminal epithelial (LE) cells are maintained at the uterine-placental interface through incorporation into trophoblast syncytial plaques. In this review, we utilize immunofluorescence microscopy to provide further insights into early syncytialization of the ovine placenta. These observations, based on results using immunofluorescence microscopy, complement and expand, not replace, our understanding of syncytialization in sheep.

In vitro culture of ovine embryos up to early gastrulating stages

Developmental failures occurring shortly after blastocyst hatching from the zona pellucida constitute a major cause of pregnancy losses in both humans and farm ungulates. The developmental events occurring following hatching in ungulates include the proliferation and maturation of extra-embryonic membranes – trophoblast and hypoblast – and the formation of a flat embryonic disc, similar to that found in humans, which initiates gastrulation prior to implantation. Unfortunately, our understanding of these key processes for embryo survival is limited because current culture systems cannot sustain ungulate embryo development beyond hatching. Here, we report a culture system that recapitulates most developmental landmarks of gastrulating ovine embryos: trophoblast maturation, hypoblast migration, embryonic disc formation, disappearance of the Rauber's layer, epiblast polarization and mesoderm differentiation. Our system represents a highly valuable platform for exploring the cell differentiation, proliferation and migration processes governing gastrulation in a flat embryonic disc and for understanding pregnancy failures during the second week of gestation.

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Luteal color doppler ultrasonography and pregnancy-associated glycoproteins as early pregnancy diagnostic tools and predictors of pregnancy loss in Bos taurus postpartum beef cows

The objective of this study was to evaluate the use of luteal color doppler (CD) ultrasonography and plasma concentrations of pregnancy-associated glycoproteins (PAG) for early pregnancy diagnosis in Bos taurus beef cows. Additionally, CD and PAG were evaluated as potential predictors of late embryonic/early fetal mortality (LEM). Postpartum beef cows (n = 212) were exposed to estrus synchronization followed by fixed-time artificial insemination (day 0). On days 20 and 22, B-mode and CD ultrasonography were performed to evaluate corpus luteum (CL) morphometries and blood perfusion. Moreover, blood samples were collected on days 25 and 29 to quantify circulating concentrations of PAG. Conventional ultrasonography on days 29 and 100 was utilized as the gold-standard method for pregnancy diagnosis. Cows that experienced pregnancy loss between days 29 and 100 were classified as LEM. Pregnant cows had larger and more vascularized CL compared with nonpregnant cows on days 20 and 22 (P < 0.001 for all response variables). Accuracy for CD on days 20 and 22 were 87% and 92%, respectively. Accuracy for PAG on days 25 and 29 were 84% and 99%, respectively. No false negative (FN) results were observed for CD on both days 20 and 22; however, there were 7.1% FN results for PAG on day 25. Cows that experienced LEM had decreased (P = 0.04) circulating PAG on day 29 of gestation compared with cows that maintained pregnancy; however, there were no differences in luteal blood perfusion on days 20 and 22 (P ≥ 0.53) or circulating PAG on day 25 (P = 0.46) between LEM cows and cows that maintained pregnancy. Sensitivity and specificity of PAG on day 29 as predictors of LEM were 83% and 77%, respectively. In conclusion, CD resulted in accurate pregnancy diagnosis in B. taurus beef cows on both days 20 and 22 of gestation, while having no FN results. Circulating concentrations of PAG were decreased in cows that experienced LEM; however, further research is required to utilize PAG as a predictor of LEM commercially.

Presence of surfactant proteins in the uteri and placentae of pregnant mares

Immunohistochemical investigations of the expression of surfactant protein A (SP-A) and surfactant protein D (SP-D) in the uterine and placental tissues of 13 pregnant mares were performed using anti-horse monoclonal primary antibodies. Strong positive reactions for both SP-A and SP-D were observed in the trophoblasts in the microcotyledons of the placentae at 182 to 314 days of gestation; in uterine glandular epithelial cells, faint-to-weak reactions were observed during gestation. This study describes, for the first time, the changes in the SP-A and SP-D expression levels in the endometrium of mares during gestation; the SP-A and SP-D expression levels increased after the second trimester of gestation.

Syncytins expressed in human placental trophoblast

Three versions of syncytiotrophoblast exist in the human placenta: an invasive type associated with the implanting conceptus, non-invasive villous type of definitive placenta, and placental bed giant cells. Syncytins are encoded by modified env genes of endogenous retroviruses (ERV), but how they contribute functionally to placental syncytial structures is unclear. A minimum of eight genes (ERVW1, ERVFRD-1, ERVV-1, ERVV-2, ERVH48-1, ERVMER34-1, ERV3-1, & ERVK13-1) encoding syncytin family members are expressed in human trophoblast, the majority from implantation to term. ERVW1 (Syncytin 1) and ERVFRD-1 (Syncytin 2) are considered the major fusogens, but, when the expression of their genes is analyzed by single cell RNAseq in first trimester placenta, their transcripts are distinctly patterned and also differ from those of their proposed binding partners, SLC1A5 and MFSD2A, respectively. ERVRH48-1 (suppressyn or SUPYN) and ERVMER34-1 are probable negative regulators of fusion and co-expressed, primarily in cytotrophoblast. The remaining genes and their products have been little studied. Syncytin expression is a feature of placental development in almost all eutherian mammals studied, in at least one marsupial, and in viviparous lizards, which lack the trophoblast lineage. Their expression has been inferred to be essential for pregnancy success in the mouse. All the main human ERV genes arose following independent retroviral insertion events, none of which trace back to the divergence of eutherians and metatherians (marsupials). While syncytins may be crucial for placental development, it seems unlikely that they helped orchestrate the divergence of eutherians and marsupials.

Peripheral action of kisspeptin at reproductive tissues-role in ovarian function and embryo implantation and relevance to assisted reproductive technology in livestock: a review

Kisspeptin (KISS1) is encoded by the KISS1 gene and was initially found to be a repressor of metastasis. Natural mutations in the KISS1 receptor gene (KISS1R) were subsequently shown to be associated with idiopathic hypothalamic hypogonadism and impaired puberty. This led to interest in the role of KISS1 in reproduction. It was established that KISS1 had a fundamental role in the control of gonadotropin releasing hormone (GnRH) secretion. KISS1 neurons have receptors for leptin and estrogen receptor α (ERα), which places KISS1 at the gateway of metabolic (leptin) and gonadal (ERα) regulation of GnRH secretion. More recently, KISS1 has been shown to act at peripheral reproductive tissues. KISS1 and KISS1R genes are expressed in follicles (granulosa, theca, oocyte), trophoblast, and uterus. KISS1 and KISS1R proteins are found in the same tissues. KISS1 appears to have autocrine and paracrine actions in follicle and oocyte maturation, trophoblast development, and implantation and placentation. In some studies, KISS1 was beneficial to in vitro oocyte maturation and blastocyst development. The next phase of KISS1 research will explore potential benefits on embryo survival and pregnancy. This will likely involve longer-term KISS1 treatments during proestrus, early embryo development, trophoblast attachment, and implantation and pregnancy. A deeper understanding of the direct action of KISS1 at reproductive tissues could help to achieve the next step change in embryo survival and improvement in the efficiency of assisted reproductive technology.

Immunohistochemical Examination of Trophoblast Syncytialization during Early Placentation in Sheep

During the peri-implantation period, multinucleated syncytia are formed in the sheep placenta. For over 20 years the scientific consensus has been that during trophoblast syncytialization in sheep, binucleate trophoblast giant cells (BNCs) differentiate from mononuclear trophoblast cells, and individual BNCs fuse with individual luminal epithelial (LE) cells to form trinucleate cells. These trophoblast-LE syncytial plaques then grow through continued BNC migration and fusion. Therefore, LE cells are thought to be incorporated into syncytial plaques. However, these ideas were based on electron microscopy studies, without benefit of molecular markers for BNC and LE cells to support conclusions. The aim of this study was to observe interactions between BNCs and uterine LE cells using immunohistochemical localization for molecular markers for BNCs and uterine LE cells. We performed immunofluorescence staining, laser capture microdissection, and TUNEL staining on the uterine-placental tissues of sheep during early placentation. We observed: (1) syncytial cells containing more than two nuclei within the trophoblast cell layer; (2) depolarized LE cells that express caspase 3 and stain positively for TUNEL; (3) engulfment of caspase 3-positive LE cells by trophoblast giant cells (TGCs) and empty spaces within the LE layer at sites of implantation; (4) rapid enlargement of syncytial plaques; and (5) E-cadherin and TUNEL-positive cells within the uterine stroma underlying degenerating LE was coincident with accumulation of CD45-positive cells at these sites. These data suggest that during early placentation: (1) fusion between trophoblasts is not limited to the formation of BNCs, and the term 'trophoblast giant cell (TGC)' may be appropriate; (2) LE cells undergo apoptosis; (3) apoptotic LE cells are eliminated by TGCs; (4) fusion is not limited to the incorporation of new BNCs but involves the lateral fusion between growing syncytial plaques; and (5) TGCs carry apoptotic LE cells away from the uterine-placental interface for elimination by immune cells within the stroma. These data indicate that uterine LE cells are not incorporated into syncytial plaques, but are engulfed and eliminated, and that early placentation in sheep is more similar to early placentation in humans than is currently understood in that both develop mononucleated cytotrophoblast and multinucleated syncytiotrophoblast layers of entirely placental origin. The elimination of LE cells by sheep TGCs might provide insights into elimination and penetration of LE cells during human embryo implantation.

Comprehensive analysis of formin localization in Xenopus epithelial cells

Reorganization of the actin cytoskeleton is crucial for cellular processes, including cytokinesis and cell–cell junction remodeling. Formins are conserved processive actin-polymerizing machines that regulate actin dynamics by nucleating, elongating, and bundling linear actin filaments. Because the formin family is large, with at least 15 members in vertebrates, there have not been any comprehensive studies examining formin localization and function within a common cell type. Here, we characterized the localization of all 15 formins in epithelial cells of Xenopus laevis gastrula-stage embryos. Dia1 and Dia2 localized to tight junctions, while Fhod1 and Fhod3 localized to adherens junctions. Only Dia3 strongly localized at the cytokinetic contractile ring. The Diaphanous inhibitory domain–dimerization domain (DID-DD) region of Dia1 was sufficient for Dia1 localization, and overexpression of a Dia1 DID-DD fragment competitively removed Dia1 and Dia2 from cell–cell junctions. In Dia1 DID-DD–overexpressing cells, Dia1 and Dia2 were mislocalized to the contractile ring, and cells exhibited increased cytokinesis failure. This work provides a comprehensive analysis of the localization of all 15 vertebrate formins in epithelial cells and suggests that misregulated formin localization results in epithelial cytokinesis failure.

Developmental peculiarities in placentae of ovine uniparental conceptuses

Genomic imprinting is an epigenetic phenomenon regulating mono-allelic expression of genes depending on their parental origin. Defective genomic imprinting is involved in several placental disorders, such as intrauterine growth restriction and pre-eclampsia. Uniparental embryos, having maternal-only or paternal-only genomes (parthenogenotes [PAR] and androgenotes [AND], respectively), are useful models to study placentation. The aim of this work was to reveal the effect of parental genome (maternal and paternal) on placentation. To do this, uniparental (AND and PAR) and biparental (CTR) in vitro produced sheep embryos transferred to recipient females were collected at day 20 of pregnancy and their placentae were analyzed. qPCR analysis showed that imprinted genes (H19, IGF2R and DLK1) were expressed accordingly to their parental origin while the expression f DNA methyltransferases () was disregulated, especially in PAR (P < 0.05). AND placentae were significantly hypomethylated compared to both PAR and CTR (P = 0.023). Chorion-allantoid of AND showed impaired development of vessels and reduced mRNA expression of vasculogenetic factors (ANG2 P = 0.05; VEGFR2 P< 0.001; TIE2 P < 0.001). Morphologically, PAR placentae were characterized by abnormal structure of the trophoectodermal epithelium and reduced total number (P<0.03) of Trophoblastic Binucleate Cells. A reduced implantation rate of both classes of uniparental embryos (P<0.03) was also noted. Our results provide new insights into the characterization of uniparental embryos and demonstrate the complementary role of parental genomes for the correct establishment of pregnancy. Thus, our findings may suggest new targets to improve our understanding of the origin of imprinting-related placental dysfunction.

The Phylogeny of Placental Evolution Through Dynamic Integrations of Retrotransposons

Trophoblasts, a major constituent of the placenta, are known to express genes derived from various endogenous retroviruses (ERVs) as well as LTR retrotransposons. However, the evolutionary significance of ERV-derived genes involved in placental development has not been well characterized. In this review, we catalog the diverse morphology of placental structure among mammalian species with note of counterintuitive developments. We then detail the history of ancient placenta development with paternally expressed gene 10 (Peg10/Sirh1), Peg11/Sirh2, and Sirh7/Ldoc1 as LTR retrotransposons, followed by independent captures of ERV-env-related genes such as Syncytin-1, -2, -A, -B, -Rum1, and Fematrin-1 responsible for trophoblast cell fusion, resulting in multinucleate syncytiotrophoblast formation, and possibly morphological diversification of placentas. Because the endogenization of retroviral infections has occurred multiple times independently in different mammalian lineages, and some use the same molecules in their transcriptional activation, we speculate that ERV gene variants integrated into mammalian genomes in a locus-specific manner have replaced the genes previously responsible for cell fusion. Moreover, ERVs also work as transcriptional regulators of various genes such as interferon (IFN)-stimulated genes. The "baton pass" hypothesis suggests that evolutionary events caused by multiple successive retrotransposon integrations, possibly resulting in effective fusogenic activity, downstream gene transcription in a temporal and spatial manner, and/or increased diversity of placental structures.

Derivation of Induced Trophoblast Cell Lines in Cattle by Doxycycline-Inducible piggyBac Vectors

Trophectoderm lineage specification is one of the earliest differentiation events in mammalian development. The trophoblast lineage, which is derived from the trophectoderm, mediates implantation and placental formation. However, the processes involved in trophoblastic differentiation and placental formation in cattle remain unclear due to interspecies differences when compared with other model systems and the small repertoire of available trophoblast cell lines. Here, we describe the generation of trophoblast cell lines (biTBCs) from bovine amnion-derived cells (bADCs) using an induced pluripotent stem cell technique. bADCs were introduced with piggyBac vectors containing doxycycline (Dox)-inducible transcription factors (Oct3⁄4(POU5F1), Sox2, Klf4, and c-Myc). Colonies that appeared showed a flattened epithelial-like morphology similar to cobblestones, had a more definite cell boundary between cells, and frequently formed balloon-like spheroids similar to trophoblastic vesicles (TVs). biTBCs were propagated for over 60 passages and expressed trophoblast-related (CDX2, ELF5, ERRβ, and IFN-τ) and pluripotency-related genes (endogenous OCT3/4, SOX2, KLF4, and c-MYC). Furthermore, when biTBCs were induced to differentiate by removing Dox from culture, they formed binucleate cells and began to express pregnancy-related genes (PL, PRP1, and PAG1). This is the first report demonstrating that the induction of pluripotency in bovine amniotic cells allows the generation of trophoblastic cell lines that possess trophoblast stem cell-like characteristics and have the potential to differentiate into the extra-embryonic cell lineage. These cell lines can be a new cell source as a model for studying trophoblast cell lineages and implantation processes in cattle.

Baton pass hypothesis: successive incorporation of unconserved endogenous retroviral genes for placentation during mammalian evolution

It is well accepted that numerous RNAs derived from endogenous retroviruses (ERVs) are expressed in mammalian reproductive structures, particularly in the uterus, trophoblast, and placenta. Syncytin 1 and syncytin 2 in humans and syncytin A and syncytin B in mice are membrane proteins originating from Env genes of ERVs. These ERVs are involved in the fusion of trophoblast cells, resulting in multinucleated syncytiotrophoblast formation. Evidence accumulated indicates that syncytin-like fusogenic proteins are expressed in the placenta of rabbits, dogs/cats, ruminant ungulates, tenrecs, and opossums. The syncytin genes so far characterized are known to be endogenized to the host genome only within the past 12-80 million years, more recently than the appearance of mammalian placentas, estimated to be 160-180 million years ago. We speculate that ERVs including syncytin-like gene variants integrated into mammalian genomes in a locus-specific manner have replaced the genes previously responsible for cell fusion. We therefore propose the 'baton pass' hypothesis, in which multiple successive ERV variants 'take over' cell-fusion roles, resulting in increased trophoblast cell fusion, morphological variations in placental structures, and enhanced reproductive success in placental mammals.

Genome variation in the trophoblast cell lifespan: Diploidy, polyteny, depolytenization, genome segregation

The lifespan of mammalian trophoblast cells includes polyploidization, its degree and peculiarities are, probably, accounted for the characteristics of placenta development. The main ways of genome multiplication-endoreduplication and reduced mitosis-that basically differ by the extent of repression of mitotic events, play, most probably, different roles in the functionally different trophoblast cells in a variety of mammalian species. In the rodent placenta, highly polyploid (512-2048c) trophoblast giant cells (TGC) undergoing endoreduplication serve a barrier with semiallogenic maternal tissues whereas series of reduced mitoses allow to accumulate a great number of low-ploid junctional zone and labyrinth trophoblast cells. Endoreduplication of TGC comes to the end with formation of numerous low-ploid subcellular compartments that show some signs of viable cells though mitotically inactive; it makes impossible their ectopic proliferation inside maternal tissues. In distinct from rodent trophoblast, deviation from (2ⁿ)c in human and silver fox trophoblast suggests a possibility of aneuploidy and other chromosome changes (aberrations, etc.). It suggests that in mammalian species with lengthy period of pregnancy, polyploidy is accompanied by more diverse genome changes that may be useful to select a more specific response to stressful factors that may appear occasionally during months of intrauterine development.

Placental Evolution within the Supraordinal Clades of Eutheria with the Perspective of Alternative Animal Models for Human Placentation

Here a survey of placental evolution is conducted. Placentation is a key factor for the evolution of placental mammals that had evolved an astonishing diversity. As a temporary organ that does not allow easy access, it is still not well understood. The lack of data also is a restriction for better understanding of placental development, structure, and function in the human. Animal models are essential, because experimental access to the human placenta is naturally restricted. However, there is not a single ideal model that is entirely similar to humans. It is particularly important to establish other models than the mouse, which is characterised by a short gestation period and poorly developed neonates that may provide insights only for early human pregnancy. In conclusion, current evolutionary studies have contributed essentially to providing a pool of experimental models for recent and future approaches that may also meet the requirements of a long gestation period and advanced developmental status of the newborn in the human. Suitability and limitations of taxa as alternative animal models are discussed. However, further investigations especially in wildlife taxa should be conducted in order to learn more about the full evolutionary plasticity of the placenta system.

A novel human endogenous retroviral protein inhibits cell-cell fusion

While common in viral infections and neoplasia, spontaneous cell-cell fusion, or syncytialization, is quite restricted in healthy tissues. Such fusion is essential to human placental development, where interactions between trophoblast-specific human endogenous retroviral (HERV) envelope proteins, called syncytins, and their widely-distributed cell surface receptors are centrally involved. We have identified the first host cell-encoded protein that inhibits cell fusion in mammals. Like the syncytins, this protein, called suppressyn, is HERV-derived, placenta-specific and well-conserved over simian evolution. In vitro, suppressyn binds to the syn1 receptor and inhibits syn1-, but not syn2-mediated trophoblast syncytialization. Suppressyn knock-down promotes cell-cell fusion in trophoblast cells and cell-associated and secreted suppressyn binds to the syn1 receptor, ASCT2. Identification of the first host cell-encoded inhibitor of mammalian cell fusion may encourage improved understanding of cell fusion mechanisms, of placental morphogenesis and of diseases resulting from abnormal cell fusion.

Structure and steroidogenesis of the placenta in the Antarctic minke whale (Balaenoptera bonaerensis)

There are few reports describing the structure and function of the whale placenta with the advance of pregnancy. In this study, therefore, the placenta and nonpregnant uterus of the Antarctic minke whale were observed morphologically and immunohistochemically. Placentas and nonpregnant uteri were collected from the 15th, 16th and 18th Japanese Whale Research Programme with Special Permit in the Antarctic (JARPA) and 1st JARPA II organized by the Institute of Cetacean Research in Tokyo, Japan. In the macro- and microscopic observations, the placenta of the Antarctic minke whale was a diffuse and epitheliochorial placenta. The chorion was interdigitated to the endometrium by primary, secondary and tertiary villi, which contained no specialized trophoblast cells such as binucleate cells, and the interdigitation became complicated with the progress of gestation. Furthermore, fetal and maternal blood vessels indented deeply into the trophoblast cells and endometrial epithelium respectively with fetal growth. The minke whale placenta showed a fold-like shape as opposed to a finger-like shape. In both nonpregnant and pregnant uteri, many uterine glands were distributed. The uterine glands in the superficial layer of the pregnant endometrium had a wide lumen and large epithelial cells as compared with those in the deep layer. On the other hand, in the nonpregnant endometrium, the uterine glands had a narrower lumen and smaller epithelial cells than in the pregnant endometrium. In immunohistochemical detection, immunoreactivity for P450scc was detected in most trophoblast cells, but not in nonpregnant uteri, suggesting that trophoblast epithelial cells synthesized and secreted the sex steroid hormones and/or their precursors to maintain the pregnancy in the Antarctic minke whale.

Application of next generation sequencing in mammalian embryogenomics: lessons learned from endogenous betaretroviruses of sheep

Endogenous retroviruses (ERVs) are present in the genome of all vertebrates and are remnants of ancient exogenous retroviral infections of the host germline transmitted vertically from generation to generation. The sheep genome contains 27 JSRV-related endogenous betaretroviruses (enJSRVs) related to the pathogenic Jaagsiekte sheep retrovirus (JSRV) that have been integrating in the host genome for the last 5-7 million years. The exogenous JSRV is a causative agent of a transmissible lung cancer in sheep, and enJSRVs are able to protect the host against JSRV infection. In sheep, the enJSRVs are most abundantly expressed in the uterine epithelia as well as in the conceptus (embryo and associated extraembryonic membranes) trophectoderm. Sixteen of the 27 enJSRV loci contain an envelope (env) gene with an intact open reading frame, and in utero loss-of-function experiments found the enJSRVs Env to be essential for trophoblast outgrowth and conceptus elongation. Collectively, available evidence supports the ideas that genes captured from ancestral retroviruses were pivotal in the acquisition of new, important functions in mammalian evolution and were positively selected for biological roles in genome plasticity, protection of the host against infection of related pathogenic and exogenous retroviruses, and a convergent physiological role in placental morphogenesis and thus mammalian reproduction. The discovery of ERVs in mammals was initially based on molecular cloning discovery techniques and will be boosted forward by next generation sequencing technologies and in silico discovery techniques.

IL-22 is expressed by the invasive trophoblast of the equine (Equus caballus) chorionic girdle

The invasive trophoblast cells of the equine placenta migrate into the endometrium to form endometrial cups, dense accumulations of trophoblast cells that produce equine chorionic gonadotropin between days 40 and 120 of normal pregnancy. The mechanisms by which the trophoblast cells invade the endometrium while evading maternal immune destruction are poorly defined. A gene expression microarray analysis performed on placental tissues obtained at day 34 of gestation revealed a >900-fold upregulation of mRNA encoding the cytokine IL-22 in chorionic girdle relative to noninvasive chorion. Quantitative RT-PCR assays were used to verify high expression of IL-22 in chorionic girdle. Additional quantitative RT-PCR analysis showed a striking increase in IL-22 mRNA expression in chorionic girdle from days 32 to 35 and an absence of IL-22 expression in other conceptus tissues. Bioinformatic analysis and cDNA sequencing confirmed the predicted length of horse IL-22, which carries a 3' extension absent in IL-22 genes of humans and mice, but present in the cow and pig. Our discovery of IL-22 in the chorionic girdle is a novel finding, as this cytokine has been previously reported in immune cells only. IL-22 has immunoregulatory functions, with primary action on epithelial cells. mRNA of IL-22R1 was detected in pregnant endometrium at levels similar to other equine epithelia. Based upon these findings, we hypothesize that IL-22 cytokine produced by the chorionic girdle binds IL-22R1 on endometrium, serving as a mechanism of fetal-maternal communication by modulating endometrial responses to trophoblast invasion.

Elephant transcriptome provides insights into the evolution of eutherian placentation

The chorioallantoic placenta connects mother and fetus in eutherian pregnancies. In order to understand the evolution of the placenta and provide further understanding of placenta biology, we sequenced the transcriptome of a term placenta of an African elephant (Loxodonta africana) and compared these data with RNA sequence and microarray data from other eutherian placentas including human, mouse, and cow. We characterized the composition of 55,910 expressed sequence tag (i.e., cDNA) contigs using our custom annotation pipeline. A Markov algorithm was used to cluster orthologs of human, mouse, cow, and elephant placenta transcripts. We found 2,963 genes are commonly expressed in the placentas of these eutherian mammals. Gene ontology categories previously suggested to be important for placenta function (e.g., estrogen receptor signaling pathway, cell motion and migration, and adherens junctions) were significantly enriched in these eutherian placenta–expressed genes. Genes duplicated in different lineages and also specifically expressed in the placenta contribute to the great diversity observed in mammalian placenta anatomy. We identified 1,365 human lineage–specific, 1,235 mouse lineage–specific, 436 cow lineage–specific, and 904 elephant-specific placenta-expressed (PE) genes. The most enriched clusters of human-specific PE genes are signal/glycoprotein and immunoglobulin, and humans possess a deeply invasive human hemochorial placenta that comes into direct contact with maternal immune cells. Inference of phylogenetically conserved and derived transcripts demonstrates the power of comparative transcriptomics to trace placenta evolution and variation across mammals and identified candidate genes that may be important in the normal function of the human placenta, and their dysfunction may be related to human pregnancy complications.

Trophoblast development

This review summarises current knowledge about the specification, commitment and maintenance of the trophoblast lineage in mice and cattle. Results from gene expression studies, in vivo loss-of-function models and in vitro systems using trophoblast and embryonic stem cells have been assimilated into a model seeking to explain trophoblast ontogeny via gene regulatory networks. While trophoblast differentiation is quite distinct between cattle and mice, as would be expected from their different modes of implantation, recent studies have demonstrated that differences arise much earlier during trophoblast development.

Endogenous retroviruses in trophoblast differentiation and placental development

Endogenous retroviruses (ERVs) are present in the genome of all vertebrates and originated from infections of the germline of the host by exogenous retroviruses. ERVs have coevolved with their hosts for millions of years and are recognized to contribute to genome plasticity, protect the host against infection of related pathogenic and exogenous retroviruses, and play a vital role in development of the placenta. Consequently, some ERVs have been positively selected and maintained in the host genome throughout evolution. This review will focus on the critical role of ERVs in development of the mammalian placenta and specifically highlight the biological role of sheep JSRV-related endogenous betaretroviruses in conceptus (embryo and associated extraembryonic membranes) development.

Viral particles of endogenous betaretroviruses are released in the sheep uterus and infect the conceptus trophectoderm in a transspecies embryo transfer model

The sheep genome contains multiple copies of endogenous betaretroviruses highly related to the exogenous and oncogenic jaagsiekte sheep retrovirus (JSRV). The endogenous JSRVs (enJSRVs) are abundantly expressed in the uterine luminal and glandular epithelia as well as in the conceptus trophectoderm and are essential for conceptus elongation and trophectoderm growth and development. Of note, enJSRVs are present in sheep and goats but not cattle. At least 5 of the 27 enJSRV loci cloned to date possess an intact genomic organization and are able to produce viral particles in vitro. In this study, we found that enJSRVs form viral particles that are released into the uterine lumen of sheep. In order to test the infectious potential of enJSRV particles in the uterus, we transferred bovine blastocysts into synchronized ovine recipients and allowed them to develop for 13 days. Analysis of microdissected trophectoderm of the bovine conceptuses revealed the presence of enJSRV RNA and, in some cases, DNA. Interestingly, we found that RNAs belonging to only the most recently integrated enJSRV loci were packaged into viral particles and transmitted to the trophectoderm. Collectively, these results support the hypothesis that intact enJSRV loci expressed in the uterine endometrial epithelia are shed into the uterine lumen and could potentially transduce the conceptus trophectoderm. The essential role played by enJSRVs in sheep reproductive biology could also be played by endometrium-derived viral particles that influence development and differentiation of the trophectoderm.

Trophoblast function in normal and preeclamptic pregnancy

Preeclampsia (PE) is a common disease of pregnancy that affects women particularly in their first pregnancies. Current estimates suggest that between 7 and 10% of pregnancies may be complicated by PE. Despite considerable research and medical efforts, the incidence of the disease has not changed substantially in the last century. In severe cases the disease may be life-threatening and is associated with high neonatal mortality and morbidity. Furthermore, therapy is often ineffective and at best treats the disease symptoms rather than the aetiology. One reason for the lack of progress may be that while the disease is generally agreed by most to be due to abnormal implantation and development of the placenta (events which happen in the first trimester) most research efforts have focused on managing and understanding the maternal disease. Since the disease typically appears in the last trimester, many weeks after the likely start of the pathology, it has been difficult to understand the progression of events. However, this picture has improved recently. The purpose here is to review how placental development is affected in PE and describe new insights into the causes. It is hoped that an understanding of the pathogenesis of the placental defects in PE will lead to new efforts towards early diagnosis, before the onset of clinical symptoms, as well as new treatments for these lesions.

Friendly viruses: the special relationship between endogenous retroviruses and their host

Endogenous retroviruses (ERVs) are present in the genome of all vertebrates and have coevolved with their hosts for millions of years. Some ERVs play a critical role in placental development, contribute to genome plasticity, and protect the host against infection of related pathogenic and exogenous retroviruses, thus some ERVs have been positively selected and maintained in the host genome. The sheep genome contains 27 endogenous retroviruses (enJSRVs) related to the pathogenic Jaagsiekte sheep retrovirus (JSRV), the causative agent of a transmissible lung cancer in sheep. enJSRVs are able to protect their host against JSRV infection by blocking different steps of the viral replication cycle. In addition, enJSRVs are absolutely required for sheep placental development. Thus, enJSRVs-JSRV provides a unique and interesting model to study the symbiotic relationship and interplay between host ERVs and evolution. This review will provide some examples of the biological functions of ERVs. In particular, the role of ERVs in reproductive biology and in protecting the host against pathogenic retrovirus infections will be emphasized using enJSRVs/JSRV and the sheep as a model.

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.

Cellular localisation of the pregnancy-associated glycoprotein family (PAGs) in the synepitheliochorial placenta of the European bison

This paper describes the cellular immuno-localisation of the PAG family in synepitheliochorial (cotyledonary) placenta of the European bison (Eb). Uteri were harvested from pregnant wild Eb (n=4; 45-150 days post coitum-dpc); and additionally from cattle (30, 45 dpc) and pigs (42 dpc)--both domestic species were used as positive controls for cellular PAG immunodetection. Placentas were sectioned, fixed, dehydrated and subjected to double fluorescent immunohistochemistry (dF-IHC) with the use of Alexa 488 fluorochrom (A488) and propidium iodide (PI). Native positive EbPAG signals were detected by heterologous (ht; cross-species) dF-IHC with primary rabbit anti-PAG polyclonals against native or recombinant porcine PAG antigens (anti-pPAG); then visualised with secondary anti-rabbit goat immunoglobulins--conjugated to A488. Our htdF-IHC indicated an unequivocal localisation to the mono- and bi-nuclear trophectoderm (chorionic epithelium) cells expressing the PAGs (A488-green) among all placental cells, in which PI (red) stained nuclei. This is the first paper reporting the EbPAG family expression examined by htdF-IHC at the feto-maternal interface in wild Pecoran species. The cross-reactivity of anti-pPAG polyclonals with the EbPAGs suggests that shared epitopes are present in these molecules. It seems that the EbPAG family, which is robustly expressed in mono- and bi-nucleated trophectoderm cells, is associated with events taking place during placenta development. Our study also provided a proficient ht-system to identify various PAGs that could be useful as prenatal protein markers for pregnancy diagnoses, which is essential for effective reproductive management of endangered mammals.

The expression of ovine placental lactogen, StAR and progesterone-associated steroidogenic enzymes in placentae of overnourished growing adolescent ewes

Overnourishing pregnant adolescent sheep promotes maternal growth but reduces placental mass, lamb birth weight and circulating progesterone. This study aimed to determine whether altered progesterone reflected transcript abundance for StAR (cholesterol transporter) and the steroidogenic enzymes (Cyp11A1, Hsd3b and Cyp17). Circulating and placental expression of ovine placental lactogen (oPL) was also investigated. Adolescent ewes with singleton pregnancies were fed high (H) or moderate (M) nutrient intake diets to restrict or support placental growth. Experiment 1: peripheral progesterone and oPL concentrations were measured in H (n=7) and M (n=6) animals across gestation (days 7-140). Experiment 2: progesterone was measured to mid- (day 81; M: n=11, H: n=13) or late gestation (day 130; M: n=21, H: n=22), placental oPL, StAR and steroidogenic enzymes were measured by qPCR and oPL protein by immunohistochemistry. Experiment 1: in H vs M animals, term placental (P<0.05), total cotyledon (P<0.01) and foetal size (P<0.05) were reduced. Circulating oPL and progesterone were reduced at mid- (P<0.001, P<0.01) and late gestation (P<0.01, P<0.05) and oPL detection was delayed (P<0.01). Experiment 2: placental oPL was not altered by nutrition. In day 81 H animals, progesterone levels were reduced (P<0.001) but not related to placental or foetal size. Moreover, placental steroidogenic enzymes were unaffected. Day 130 progesterone (P<0.001) and Cyp11A1 (P<0.05) were reduced in H animals with intrauterine growth restriction (H+IUGR). Reduced mid-gestation peripheral oPL and progesterone may reflect altered placental differentiation and/or increased hepatic clearance respectively. Restricted placental growth and reduced biosynthesis may account for reduced progesterone in day 130 H+IUGR ewes.

Mitotic polyploidization in trophoblast giant cells of the alpaca

Genome multiplication is a typical feature of trophoblast giant cell (TGC) development in many species. Elevated nuclear DNA contents can be achieved by modified cell cycles with a complete lack of mitosis (endoreduplication) or with incomplete mitoses. The aim of this study is to characterize genome multiplication in the alpaca TGC. Placental tissues of gestation days 150, 264 and 347 (near term) and term placentae were processed for light microscopy and for transmission electron microscopy. Each TGC showed many nuclear profiles. Observation of serial sections revealed that TGCs are truly multinucleate with several highly lobulated nuclei. Feulgen staining showed that TGC nuclei have a higher DNA content than nuclei of other trophoblast cells. The number of argyrophilic nucleolar organizer regions (AgNORs) in nuclear profiles of TGC was between 15 and 100, while other trophoblast cells showed 1 or 2 AgNORs. Large multipolar mitotic figures with maximal diameters of 80 mum were observed in the alpaca placentas on gestation days 264 and 347. No cytokinesis was seen in TGC. The results show that the mode of genome multiplication in the alpaca TGC is mitotic polyploidization. Subsequent acytokinetic mitoses may lead to an accumulation of chromosomes and centrioles in TGC. With increasing ploidy levels, the shape of these polyploidizing mitoses becomes more irregular. The restitution of nuclei after these complex multipolar mitoses is likely to result in the irregular nuclear shape in TGC.

Induction of Intrauterine Growth Restriction by Reducing Placental Vascular Growth with the Angioinhibin TNP-470

The placenta is a specialized vascular interface between the maternal and fetal circulations that increases in size to accommodate the nutritional and metabolic demands of the growing fetus. Vascular proliferation and expansion are critical components of placental development and, consequently, interference with vascular growth has the potential to severely restrict concurrent development of both the placenta and fetus. In this study, we describe the effects of an antiangiogenic agent, TNP-470, on placental vascular development and the induction of a form of intrauterine growth restriction (IUGR) in mice. Administration of TNP-470 to dams in the second half of pregnancy resulted in a smaller maternal weight gain accompanied by decreased placental and fetal sizes in comparison with control animals. Total numbers of fetuses per litter were not affected significantly. Stereological analysis of placentas revealed no changes in the combined lengths of vessels. However, the mean cross-sectional areas of maternal and fetal vessels in the labyrinth of TNP-470-treated mice were reduced at Embryonic Day 13.5 (E13.5) but not at E18.5. Further analysis showed reduced placental endothelial proliferation at E13.5 and E18.5 in TNP-470-treated animals. No other structural or morphometric differences in placentas were detected between TNP-470-treated and control mice at E18.5. This study provides conclusive evidence that administration of TNP-470 interferes with placental vascular proliferation and vessel caliber and results in a reproducible model of IUGR.

Temporospatial expression of placental lactogen and prolactin-related protein-1 genes in the bovine placenta and uterus during pregnancy

The anatomical location of binucleate cells (BNC) influences protein expression but not steroid synthesis in ruminants. In order to determine if BNC in disparate locations differentially express bovine placental lactogen (bPL) and prolactin-related protein-1 (bPRP-1), we quantitated bPL and bPRP-1 transcripts in placentomal (cotyledonary, caruncular) and interplacentomal (intercotyledonary, intercaruncular) tissues throughout pregnancy in the bovine using real-time reverse transcription PCR (RT-PCR) and in situ hybridization. Levels of both bPL and bPRP-1 transcripts at peri-implantation were significantly higher (P < 0.01) in the fetal membrane than in caruncular and intercaruncular tissues. Thereafter, mRNA for these related proteins demonstrated different spatial as well as temporal patterns of expression. Levels of bPRP-1 transcripts peaked at day 60 of pregnancy. Between day 60 and 100, bPRP-1 transcripts fell by approximately sevenfold (P < 0.01) in cotyledonary and intercotyledonary tissues, and fourfold in caruncular (P < 0.01) tissue. Levels of bPRP-1 transcripts remained low in the cotyledonary, intercotyledonary, and caruncular tissues until peripartum. In contrast, bPL expression in placentomes increased with progression of gestation (P < 0.01), but decreased in interplacentomal tissue around peripartum. To conclude, disparate patterns of bPRP-1 and bPL genes are transcribed in the placentomal and interplacentomal tissues during gestation in the bovine, suggesting that these prolactin-like hormones serve distinct functions and are regulated differently in the uteroplacental unit in this species.

The cytoplasmic expression of E-cadherin and beta-catenin in bovine trophoblasts during binucleate cell differentiation

Binucleate cells are endocrine cells generated by the acytokinesis and endoreduplication of the trophectoderm in the ruminant placenta. These cells are migratory and secrete hormones into the maternal circulation after fusing with uterine epithelial cells. In this study, we performed immunohistochemistry for E-cadherin and beta-catenin in bovine placenta and a bovine trophoblast cell line (BT-1). We found that E-cadherin and beta-catenin were distributed not only at the cell to cell boundary but throughout the cytoplasm in binucleate cells, although they were concentrated at the cell to cell boundary in epithelial cells in bovine placenta. Moreover, beta-catenin was detected in the nuclei of binucleate cells. Binucleate cells after fusion with uterine epithelial cells (feto-maternal hybrid cells) in the maternal side showed no intracellular expression of E-cadherin and beta-catenin. The transformation into binucleate cells in the BT-1 cell line was also accompanied by the cytoplasmic accumulation of E-cadherin and beta-catenin. We further demonstrated that levels of cytoplasmic beta-catenin were well correlated with the DNA content of binucleate cells in BT-1. The dynamic changes in the distribution of E-cadherin and beta-catenin suggest an important role in binucleate cells, including the rearrangement of cadherin-mediated cell adhesions during cell migration and the onset of endoreduplication probably via the nuclear transfer of beta-catenin.

Sheep Endogenous Betaretroviruses (enJSRVs) and the Hyaluronidase 2 (HYAL2) Receptor in the Ovine Uterus and Conceptus

The ovine genome contains approximately 20 copies of endogenous betaretroviruses (enJSRVs) that are highly related to two exogenous oncogenic viruses, Jaagsiekte sheep retrovirus (JSRV) and Enzootic nasal tumor virus. The cellular receptor for both JSRV and the enJSRVs is hyaluronidase 2 (HYAL2). In this study, we assessed expression of enJSRVs envelope (env) and HYAL2 mRNAs in the ovine uterus and conceptus (embryo/fetus and extraembryonic membranes) throughout gestation. By reverse transcription-polymerase chain reaction analyses, enJSRVs env were found to be expressed beginning in the Day 12 conceptus, whereas HYAL2 was expressed from Day 16. HYAL2 mRNA was detected throughout gestation in the placentome but not in the endometrium, whereas enJSRVs env expression was detected throughout gestation in endometrium and placentomes. The enJSRVs env mRNA was specifically expressed in the endometrial lumenal epithelium (LE) and glandular epithelium (GE) as well as the trophoblast giant binucleate cells (BNC) and multinucleated syncytia of the placenta. HYAL2 mRNA was only detected in the BNC and multinucleated syncytial plaques of the placentome. Partial sequencing of the transcriptionally active enJSRVs from sheep endometrium, placentomes, and placenta revealed expression of many enJSRV loci. Cloning of the expressed enJSRVs env mRNA from ovine uteroplacental tissues found sequences similar to the previously identified enJS5F16 and enJS56A1 gene with an intact open reading frame, although the polypeptides they encode were not studied. Collectively, results provide further support for our hypothesis that the enJSRVs Env have been beneficial to the host and are involved in protection of the uterus from viral infection and regulators of placental morphogenesis and function.

Developmental indices of nutritionally induced placental growth restriction in the adolescent sheep

Most intrauterine growth restriction cases are associated with reduced placental growth. Overfeeding adolescent ewes undergoing singleton pregnancies restricts placental growth and reduces lamb birth weight. We used this sheep model of adolescent pregnancy to investigate whether placental growth restriction is associated with altered placental cell proliferation and/or apoptosis at d 81 of pregnancy, equivalent to the apex in placental growth. Adolescent ewes with singleton pregnancies were offered a high or moderate level of a complete diet designed to induce restricted or normal placental size at term, respectively. Bromodeoxyuridine (Brd-U) was administered to H and M ewes 1 h before slaughter. Placental tissues were examined for a) Brd-U (immunohistochemistry) and b) apoptosis regulatory genes by in situ hybridization, Northern analyses (bax, mcl-1), immunohistochemistry, and Western analyses (bax). Quantification was carried out by image analysis. Total placentome weights were equivalent between groups. Brd-U predominantly localized to the trophectoderm and was significantly lower in the H group. Bax and mcl-1 mRNA were localized to the maternal-fetal interface. Bax protein was significantly increased in the H group and predominant in the uninuclear fetal trophectoderm. These observations indicate that reduced placental size at term may be due to reduced placental cell proliferation and possibly increased apoptosis occurring much earlier in gestation.

Implantation mechanisms: insights from the sheep

Implantation in all mammals involves shedding of the zona pellucida, followed by orientation, apposition, attachment and adhesion of the blastocyst to the endometrium. Endometrial invasion does not occur in domestic ruminants; thus, definitive implantation is achieved by adhesion of the mononuclear trophoblast cells to the endometrial lumenal epithelium (LE) and formation of syncytia by the fusion of trophoblast binucleate cells with the LE. This review highlights new information on mechanisms regulating the implantation cascade in sheep. The embryo enters the uterus on day 4 at the morula stage of development and then develops into a blastocyst by day 6. The blastocyst sheds the zona pellucida (day 8), elongates to a filamentous form (days 11–16), and adheres to the endometrial LE (day 16). Between days 14 and 16, the binucleate cells begin to differentiate in the trophoblast and subsequently migrate and fuse with the endometrial LE to form syncytia. Continuous exposure of the endometrium to progesterone in early pregnancy downregulates the progesterone receptors in the epithelia, a process which is associated with loss of the cell-surface mucin MUC1 and induction of several secreted adhesion proteins. Recurrent early pregnancy loss in the uterine gland knockout ewe model indicates that secretions of the endometrial epithelia have a physiologic role in blastocyst elongation and implantation. A number of endometrial proteins have been identified as potential regulators of blastocyst development and implantation in sheep, including glycosylated cell adhesion molecule 1 (GlyCAM-1), galectin-15, integrins and osteopontin. The epithelial derived secreted adhesion proteins (GlyCAM-1, galectin-15 and osteopontin) are expressed in a dynamic temporal and spatial manner and regulated by progesterone and/or interferon tau, which is the pregnancy recognition signal produced by the trophoblast during blastocyst elongation. The noninvasive and protracted nature of implantation in domestic animals provides valuable opportunities to investigate fundamental processes of implantation that are shared among all mammals. Understanding of the cellular and molecular signals that regulate uterine receptivity and implantation can be used to diagnose and identify causes of recurrent pregnancy loss and to improve pregnancy outcome in domestic animals and humans.

Angiogenin distribution in human term placenta, and expression by cultured trophoblastic cells

Human angiogenin is a 14-kDa secreted protein with angiogenic and ribonucleolytic activities. Angiogenin is associated with tumour development but is also present in normal biological fluids and tissues. To further address the physiological role of angiogenin, we studied its expression in situ and in vitro, using the human term placenta as a model of physiological angiogenesis. Angiogenin was immunodetected by light and transmission electron microscopy, and its cellular distribution was established by double immunolabelling with cell markers including von Willebrand factor, platelet/endothelial cell adhesion molecule-1 (PECAM-1), CD34, Tie-2, vascular endothelial cadherin (VE-cadherin), vascular endothelial growth factor receptor-2 (VEGF-R2), erythropoeitin receptor (Epo-R), alpha-smooth muscle actin, CD45, cytokeratin 7, and Ki-67. Angiogenin immunoreactivity was detected in villous and extravillous trophoblasts, the trophoblast basement membrane, the endothelial basal lamina, foetal blood vessels, foetal and maternal red blood cells, and amnionic cells. Its expression was confirmed by in situ hybridisation with a digoxygenin-labelled cDNA probe and reverse transcriptase-polymerase chain reaction amplification. Villous cytotrophoblasts, isolated and differentiated in vitro into a functional syncytiotrophoblast, expressed and secreted angiogenin. Given its known biological activities in vitro and its observed pattern of expression, these data suggest that, in human placenta, angiogenin has a role not only in angiogenesis but also in vascular and tissue homeostasis, maternal immune tolerance of the foetus, and host defences.

Trophoblast gene expression: transcription factors in the specification of early trophoblast

Azone of trophoblast specification is established when the embryo is a morula, presumably reflecting a unique combination of transcription factors in that zone of cells and the influence of various environmental cues and growth factors on them. A key first step in this process of specification is the down-regulation of Oct4, a transcription factor that acts as a negative regulator of trophoblast specification and of genes normally up-regulated as the trophectoderm first forms. The transcription factors believed to have a positive association with trophectoderm specification have been inferred primarily in two ways: by their expression patterns in embryos, ES cells and TS cells and by the consequences of gene disruption on embryonic development. Many of these transcription factors also control the expression of genes characteristically expressed in trophoblast but not in the epiblast, primitive endoderm and their derivatives. ES and TS cells from the mouse and other species are beginning to provide insights into the changes in gene expression that accompany lineage specification and the subsequent post-specification events that lead to functional trophoblast derivatives.

Trophoblast differentiation in vitro: establishment and characterisation of a serum-free culture model for murine secondary trophoblast giant cells

Differentiation of trophoblast giant cells is an early event during the process of murine embryo implantation. However, differentiation of secondary trophoblast giant cells in the rodent is still only partially understood, probably because of the lack of suitablein vitromodels and cell markers. In order to advance our understanding of trophoblast differentiation, suitablein vitromodels and markers are required to study their development. The objectives of this study were to establish and characterise a serum-freein vitromodel for murine secondary trophoblast cells. Secondary trophoblast giant cells growingin vitroand paraffin sections of day 8.5 postcoitum mouse embryos were processed for immunostaining to establish the expression of potential markers using antibodies to blood group antigens, E-cadherin, α7integrins and activator protein-γ, as well as placental lactogen-II. Within 3 days in serum-free culture, ectoplacental cone-derived secondary trophoblast cells underwent simultaneous induction of both morphological and functional differentiation. Secondary trophoblasts grewin vitroas a monolayer of cells with giant nuclei and expressed B and Le-b/Le-y blood group antigens, α7integrins and placental lactogen-II, as well as activator protein-γ. Transcripts for activator protein-γ and placental lactogen-II were detected in cultures by RT-PCR and for placental lactogen-II byin situhybridisation. At later time-points apoptosis increased. A fibronectin substrate significantly increased secondary trophoblast cell numbers and surface area of outgrowth. The increase in cells with giant nuclei coincided with induction of placental lactogen-II expression. A relationship was found between the nuclear area of secondary trophoblast cells and expression of placental lactogen-II.

Indoleamine 2,3-dioxygenase expression is restricted to fetal trophoblast giant cells during murine gestation and is maternal genome specific

Pharmacologic inhibition of indoleamine 2,3 dioxygenase (IDO) activity during murine pregnancy results in rejection of allogeneic fetuses by the maternal immune system. Here, we show that IDO expression is restricted to perinuclear regions of primary trophoblast giant cells (TGCs) of fetal origin at mid-gestation (E10.5). After placentation (E14), no IDO expression was detected at the maternal-fetal interface. Matings involving IDO-deficient females revealed that paternally inherited IDO alleles were inactive in primary TGCs, presumably due to paternal genome-specific gene inactivation. Allogeneic matings in which both parents were genetically IDO-deficient produced litters of normal sizes at normal rates compared to IDO-sufficient parental mice, implying that compensatory or redundant immunosuppressive mechanisms protected allogeneic fetuses during gestation in IDO-deficient mice. Consistent with this notion, treatment with IDO inhibitor did not affect allogeneic pregnancy rates when both parents were IDO-deficient, confirming that IDO was the relevant pharmacologic target of the IDO inhibitor in matings involving IDO-sufficient mice. Hence, IDO is a key immunosuppressive mechanism in normal murine pregnancies, and it is regulated entirely through maternally inherited fetal genes.

Antiphosphatidylserine Antibodies Affect Rat Yolk Sacs in Culture: a Mechanism for Fetal Loss in Antiphospholipid Syndrome

PROBLEM

A variety of reproductive impairments have been reported in the context of the antiphospholipid syndrome (APS). APS is associated with the presence of antibodies to negatively charged phospholipids that may affect the outcome of pregnancy.

METHOD OF STUDY

Rat embryos were cultured within their yolk sacs. The effects of two antiphosphatidylserine monoclonal aPS antibodies (HL5B, RR7F) regarding their influence on growth and apoptotic events of the yolk sacs, as well as on growth and the morphology of the embryos, were studied.

RESULTS

Exposure of rat embryos and their yolk sacs to aPS inhibited yolk sac growth. Moreover, increased number of apoptotic events of giant cells in the aPS-exposed ectoplacental cone was found in comparison with control IgG-exposed giant cells (P < 0.05). No significant damage was observed in the embryos.

CONCLUSIONS

The results suggest that aPS affect growth and apoptosis of rat ectoplacental cone.

Involvement of calcitonin gene-related peptide in control of human fetoplacental vascular tone

Calcitonin gene-related peptide (CGRP), one of the most potent endogenous vasodilators known, has been implicated in vascular adaptations and placental functions during pregnancy. The present study was designed to examine the existence of CGRP-A receptor components, the calcitonin receptor-like receptor (CRLR) and receptor activity-modifying protein 1 (RAMP1), in the human placenta and the vasoactivity of CGRP in the fetoplacental circulation. Immunofluorescent staining of the human placenta in term labor using polyclonal anti-CRLR and RAMP1 antibodies revealed that labeling specifically concentrated in the vascular endothelium and the underlying smooth muscle cells in the umbilical artery/vein, chorionic artery/vein, and stem villous vessels as well as in the trophoblast layer of the placental villi. In vitro isometric force measurement showed that CGRP dose dependently relaxes the umbilical artery/vein, chorionic artery/vein, and stem villous vessels. Furthermore, CGRP-induced relaxation of placental vessels are inhibited by a CGRP receptor antagonist (CGRP8–37), ATP-sensitive potassium (KATP) channel blocker (glybenclamide), and cAMP-dependent protein kinase A inhibitor (Rp-cAMPS) and partially inhibited by a nitric oxide inhibitor ( Nω-nitro-l-arginine methyl ester). We propose that CGRP may play a role in the control of human fetoplacental vascular tone, and the vascular dilations in response to CGRP may involve activation of KATP channels, cAMP, and a nitric oxide pathway.

Developmental changes in the ploidy of mouse implanting trophoblast cells in vitro

Shortly after the onset of implantation, polar mouse trophoblast cells proliferate and give rise to the ectoplacental cone, constituted by two distinct cell populations: undifferentiated, diploid cells and giant cells. Giant cells characteristically exhibit exaggerated dimensions and polyploid nuclei. In this study, we employ ectoplacental cones as a dynamic source of trophoblast giant cells to analyze cell proliferation, cell death, and ploidy under in vitro conditions. Our results show that DNA synthesis and the increase in the cell number are relevant only during the first 24 h of culture. Subsequently, DNA synthesis still occurs, mainly in the giant cell compartment, while the number of cells gradually decreases. Cell death by injury and apoptosis was also observed in the non-giant cell compartment of the ectoplacental cone. These findings suggest that the first 24 h of culture are crucial to the mitotic activity of the ectoplacental cone cells that gradually ceases, favoring the endoreduplication process. The DNA synthesis index during the subsequent experimental intervals emphasizes accumulation of DNA for the polyploidization. There was clear correlation between DNA content and nuclear dimension. The ploidy values for the trophoblast giant cells varied from 2C up to 368C in the giant cells, but were not as expressive as those known from in vivo conditions, probably due to the absence of regulatory factors specific to the embryonic-maternal interface. In situ hybridization and histochemistry for the nucleolus-organizing region showed that trophoblast nuclei have only two marker signals, indicative of a typical polytenic process. This present study elucidates important aspects of trophoblast behavior and provides new information on trophoblast physiology in vivo and in vitro.

Effect of high concentrations of glucose on differentiation of rat trophoblast cells in vitro

AIMS/HYPOTHESIS

Previous studies have shown that diabetic placentas are characterized by structural and biochemical anomalies, including defects in the differentiation of trophoblasts. In this study, the Rcho-1 cell line was used to investigate the impact of high glucose concentrations on different markers of differentiation of rat trophoblast cells in giant cells (endoreduplication, invasive phenotype and endocrine phenotype).

MATERIALS

Rcho-1 cells were incubated for 12 days in medium supplemented with different concentrations of glucose and 10% horse serum to optimize differentiation. The cells were examined for the proportion of nuclei showing signs of apoptosis. The effect of high glucose was investigated on the endoreduplication process, on invasive phenotype (secretion of gelatinase B) and on endocrine phenotype (expression of placental lactogen I (PL-I) and II (PL-II) and progesterone secretion).

RESULTS

Apoptosis was not induced by high glucose in Rcho-1. The number of cells was higher in the cultures exposed to high glucose (p<0.05) and their nuclei contained more DNA compared with control cells (p<0.001), while their nuclear size was smaller (p<0.001). Gelatinase B secretion increased during differentiation but no difference was found when gelatinase B secretion from trophoblasts exposed to high glucose was compared with the control cells. Rcho-1 cell cultures showed an increase in PL-I and PL-II mRNA expressions during differentiation and which was not affected by high glucose. Progesterone secretion increased during differentiation in control cultures. However, this increase was abolished when trophoblasts were cultured in high glucose.

CONCLUSIONS/INTERPRETATION

Our data suggest that high glucose influences the endoreduplication process and the steroidogenesis during differentiation of rattrophoblasts.

Specializations of the chorioallantoic placenta in the Brazilian scincid lizard, Mabuya heathi: a new placental morphotype for reptiles

New World skinks of the genus Mabuya exhibit a unique form of viviparity that involves ovulation of tiny (1 mm) eggs and provision of virtually all of the nutrients for embryonic development by placental means. Studies of the Brazilian species M. heathi reveal that the chorioallantoic placenta is unlike those reported in any other squamate genus and exhibits striking specializations for maternal-fetal nutrient transfer. The uterine lining is intimately apposed to the chorioallantois, with no trace of an intervening shell membrane or of epithelial erosion; thus, the placenta is epitheliochorial. The uterus exhibits multicellular glands that secrete organic material into the uterine lumen. Opposite the openings of these glands, the chorion develops areolae, invaginated pits that are lined by absorptive, columnar epithelium. A single, mesometrial placentome develops, formed by radially oriented uterine folds that project into a deep invagination of the chorion. Uterine epithelium of the placentome appears to be syncytial and secretory and overlies a rich vascular supply. The apposed chorionic epithelium is absorptive in morphology and contains giant binucleated cells that bear microvilli. Several specializations of the placental membranes of M. heathi are found among eutherian mammals, signifying evolutionary convergence that extends to histological and cytological levels. The chorioallantoic placenta of M. heathi and its relatives warrants recognition as a new morphotype for reptiles, defined here as the "Type IV" placenta. This is the first new type of chorioallantoic placenta to be defined formally for reptiles in over half a century.

Trophoblast giant-cell differentiation involves changes in cytoskeleton and cell motility

Trophoblast giant-cell differentiation is well-characterized at the molecular level, yet very little is known about how molecular changes affect the cellular functions of trophoblast in embryo implantation. We have found, using both explanted E7.5 mouse embryo ectoplacental cone and the rat choriocarcinoma (Rcho-1) cell line, that trophoblast differentiation is distinguished by dramatic changes in cytoarchitecture and cell behavior. Undifferentiated trophoblast cells contain little organized actin and few small, peripheral focal complexes and exhibit high membrane protrusive activity, while differentiated trophoblast giant cells contain prominent stress fibers, large internal as well as peripheral focal adhesions, and become immotile. The dramatic changes in cell behavior and cytoskeletal organization of giant cells correlate with changes in the activities of the Rho family of small GTPases and a decrease in tyrosine phosphorylation of focal adhesion kinase. Together, these data provide detailed insight into the cellular properties of trophoblast giant cells and suggest that giant-cell differentiation is characterized by a transition from a motile to a specialized epithelial phenotype. Furthermore, our data support a phagocytic erosion, rather than a migratory infiltration, mechanism for trophoblast giant-cell invasion of the uterine stroma.

Genes regulating embryonic and fetal survival

Embryonic mortality in both farm animals and humans occurs most frequently during the first few weeks after conception. It can be attributed to abnormalities in the earliest developmental processes during embryogenesis that include implantation, maternal recognition of pregnancy, and formation of the placenta and cardiovascular system. The molecular mechanisms that are essential for all of these early processes are being elucidated at a rapid pace using transgenic and gene knockout approaches in mice. Two important general conclusions have emerged from this work. First, placental defects can occur by a number of different molecular mechanisms and can result from defects in the development or function of its trophoblast, mesenchymal or vascular components. Second, placental and cardiovascular functions are intimately linked. Cells of the placenta, for example, produce hormones that have profound effects on maternal and fetal cardiac and vascular function. In addition, development of the two is linked mechanistically through the use of some genes that are essential for development of both. Understanding the molecular basis of these processes should help to address the major limits to the success of embryo transfer, IVF and embryo cloning practices in livestock species.

Immunolocalization of gastrin-releasing peptide in the bovine uterus and placenta

Gastrin-releasing peptide (GRP), a mammalian homologue of amphibian bombesin, has been suggested to be a novel regulatory peptide in the reproductive tract during pregnancy. In this study, the localization of GRP in the bovine uterus and placenta was demonstrated by immunohistochemistry. Uterine and placental samples were collected from nonpregnant and pregnant specimens, respectively. Tissue sampling was done from the caruncle and intercaruncle of the uterus, and from the placentome (caruncle and cotyledon) and intercotyledon of the placenta. In all the tissues examined, GRP was detected although its immunoreactivity was observed at various degrees. In the uterus, moderate immunoreactivity for GRP was observed in the uterine gland epithelial cells. In the placenta, strong immunoreactivity for GRP was demonstrated in the uterine gland epithelial cells; moderate in superficial epithelial cells; and weak in the trophoblasts, trophoblastic giant cells and cryptal epithelial hybrid cells. In both nonpregnant and pregnant animals, GRP was immunolocalized in the uterine gland secretions and was found predominantly in the supranuclear region of the uterine gland epithelial cells. These findings may suggest that GRP is secreted into the uterine lumen and regulates the intrauterine environment of both the nonpregnant and pregnant bovine by exocrine, autocrine and/or paracrine manner.