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  • Abstract: placenta x
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P. M. G. Barends, H. W. J. Stroband, N. Taverne, G. te Kronnie, M. P. J. M. Leën and P. C. J. Blommers

Summary. The embryonic ectoderm of the pig differentiated and became part of the outer barrier of the blastocyst (earlier formed by the trophectoderm alone) before shedding of the overlying polar trophectoderm around Day 10, thus securing the integrity of the rapidly expanding blastocyst. Ferritin, added to the medium of the blastocyst, was taken up rapidly by trophectoderm cells, but did not reach the blastocoele, and consequently no tracer was found within hypoblast cells. Embryonic ectoderm cells did not absorb the macromolecule, before or after loss of the polar trophectoderm. When ferritin was injected into the blastocoele, trophectoderm, hypoblast and embryoblast cells all absorbed the tracer. At Day 11, blastocyst diameter and embryoblast cell number varied widely and were hardly correlated. We suggest that embryoblast development may be a more reliable indicator for the developmental stage of a blastocyst than its diameter, which may merely be an indication of the viability of the trophoblast.

Keywords: pig; blastocyst; ultrastructure; developmental variation

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S. Lindenberg, S. J. Kimber and E. Kallin

Summary. Mouse blastocysts bound LNF I conjugated to BSA-FITC or HSA-FITC and binding was inhibited by LNF I-HSA and to some extent by free LNF I, suggesting that the trophectoderm carries receptors specific for LNF I-like structures previously shown to be involved in implantation.

Keywords: embryo; implantation; neoglycoprotein; receptor; trophoblast, mouse

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F. B. P. Wooding, T. Hobbs, G. Morgan, R. B. Heap and A. P. F. Flint

This paper demonstrates that in sheep and goats the two definitive fetomaternal interface layers are developmentally related. The fetal trophectoderm consists of binucleate and uninucleate cells. The apical microvilli of the trophectoderm interdigitate with a layer consisting of syncytial plaques of limited area bounding the maternal connective tissue. Our previous histological ultrastructural and immunocytochemical work has indicated that throughout pregnancy the fetal binucleate cells migrate to and fuse with the uterine epithelium or its derivatives to form these syncytial plaques which constitute a persistent fetomaternal tissue unique to ruminants. This quantitative autoradiographic study of thymidine incorporation into sheep and goat placentas confirms the central role of the binucleate cell in placental growth, demonstrates that throughout pregnancy all binucleate cells migrate and indicates that most of the nuclei of the syncytial plaques, which appear to have a limited lifespan, derive from binucleate cell fusion.

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S. Lindenberg, K. Sundberg, S. J. Kimber and A. Lundblad

Summary. Seven oligosaccharides isolated from human milk were tested for their effect in an in-vitro model of mouse blastocyst adhesion and trophoblast outgrowth on endometrial epithelial monolayers. One compound, lacto-N-fucopentaose I (LNF I), produced a significant reduction in the percentage of attached and outgrown blastocysts after co-culture for 72 h (P < 0·001). No significant effect of any other tested oligosaccharide was obtained.

Keywords: trophectoderm; uterine–epithelial cells; blastocyst; oligosaccharides; attachment; in vitro

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C Allison Gray, Kathrin A Dunlap, Robert C Burghardt and Thomas E Spencer

Galectin-15 is the newest member of a secreted β-galactoside-binding lectin family. The galectin-15 gene is expressed specifically by the endometrial luminal epithelium (LE) and superficial ductal glandular epithelium (sGE) of the ovine uterus. The proposed extracellular role of secreted galec7tin-15 is to regulate implantation and placentation by functioning as a heterophilic cell adhesion molecule between the conceptus trophectoderm and endometrial LE, while that of intracellular galectin-15 is to regulate cell survival, differentiation and function. The present study determined galectin-15 expression in uteroplacental tissues during gestation and in the postpartum uterus. In the uterine lumen, secreted galectin-15 was found as multimers, particularly on days 14 and 16 of pregnancy. In the endometrial epithelium and conceptus trophectoderm, intracellular galectin-15 protein was found associated with crystalline structures. Between days 20 and 120 of pregnancy, galectin-15 mRNA was expressed specifically by the LE and sGE of the intercaruncular endometrium of ewes. Immunoreactive galectin-15 protein was most abundant in the trophectoderm with lower levels in the endometrial LE and sGE. Galectin-15 protein was detected in allantoic fluid, but not in amniotic fluid. After parturition, galectin-15 mRNA declined in the endometrium from postpartum day (PPD) 1 to 28 and exhibited a variegated expression pattern in the LE and sGE. These results indicate that galectin-15 is synthesized and secreted throughout gestation by the endometrial LE/sGE and is absorbed by the placenta and forms crystals within the trophectoderm, whereas the remainder is cleared into the allantois after being transported into the fetal circulation via the placental areolae. Based on the biological properties of other galectin family members, galectin-15 is hypothesized to have biological roles in conceptus–endometrial interactions, uterine immune and inflammatory responses, and placental morphogenesis and function.

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Chiara Mannelli, Anna Z Szóstek, Karolina Lukasik, Claudiopietro Carotenuto, Francesca Ietta, Roberta Romagnoli, Cristina Ferretti, Luana Paulesu, Slawomir Wołczynski and Dariusz Jan Skarzynski

The human endometrium is a fertility-determining tissue and a target of steroid hormones' action. Endocrine disruptors (EDs) can exert adverse effects on the physiological function of the decidua at the maternal–fetal interface. We examined the potential effects of an ED, bisphenol A (BPA), on endometrial maturation/decidualization, receptivity, and secretion of decidual factors (biomarkers). In vitro decidualized, endometrial stromal cells from six hysterectomy specimens were treated with 1 pM–1 μM of BPA, for 24 h and assessed for cell viability and proliferation. Three non-toxic concentrations of BPA (1 μM, 1 nM, and 1 pM) were selected to study its influence on secretion of cell decidualization biomarkers (IGF-binding protein and decidual prolactin (dPRL)), macrophage migration inhibitory factor (MIF) secretion, and hormone receptors' expression (estrogen receptors (ERα and ERβ); progesterone receptors (PRA and PRB); and human chorionic gonadotropin (hCG)/LH receptor (LH-R)). The results showed a decrease in cell viability (P<0.001) in response to BPA at the level of 1 mM. At the non-toxic concentrations used, BPA perturbed the expression of ERα, ERβ, PRA, PRB, and hCG/LH-R (P<0.05). Furthermore, 1 μM of BPA reduced the mRNA transcription of dP RL (P<0.05). Secretion of MIF was stimulated by all BPA treatments, the lowest concentration (1 pM) being the most effective (P<0.001). The multi-targeted disruption of BPA on decidual cells, at concentrations commonly detected in the human population, raises great concern about the possible consequences of exposure to BPA on the function of decidua and thus its potential deleterious effect on pregnancy.

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Fuller W Bazer, Thomas E Spencer, Greg A Johnson, Robert C Burghardt and Guoyao Wu

Uterine receptivity to implantation of blastocysts in mammals includes hatching from zona pellucida, precontact with uterine luminal (LE) and superficial glandular (sGE) epithelia and orientation of blastocyst, apposition between trophectoderm and uterine LE and sGE, adhesion of trophectoderm to uterine LE/sGE, and, in some species, limited or extensive invasion into the endometrial stroma and induction of decidualization of stromal cells. These peri-implantation events are prerequisites for pregnancy recognition signaling, implantation, and placentation required for fetal–placental growth and development through the remainder of pregnancy. Although there is a range of strategies for implantation in mammals, a common feature is the requirement for progesterone (P4) to downregulate expression of its receptors in uterine epithelia and P4 prior to implantation events. P4 then mediates its effects via growth factors expressed by stromal cells in most species; however, uterine luminal epithelium may express a growth factor in response to P4 and/or estrogens in species with a true epitheliochorial placenta. There is also compelling evidence that uterine receptivity to implantation involves temporal and cell-specific expression of interferon (IFN)-stimulated genes that may be induced directly by an IFN or induced by P4 and stimulated by an IFN. These genes have many roles including nutrient transport, cellular remodeling, angiogenesis and relaxation of vascular tissues, cell proliferation and migration, establishment of an antiviral state, and protection of conceptus tissues from challenges by the maternal immune cells.

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Jeffrey W. Pollard

Department of Developmental Biology and Cancer, Albert Einstein College of Medicine, 1300 Morris Park Ave, Bronx, NY 10461, USA

Keywords: colony stimulating factor-1; uterus; placenta; growth factor; mouse; rat

Introduction

During the preimplantation period the rodent uterus undergoes a complex programme of cell proliferation and differentiation that concludes with the uterus becoming receptive to the blastocyst for implantation. At the site of trophectoderm invasion the uterine epithelium breaks down and the underlying stroma undergoes decidualization. These decidual cells and the invading trophoblasts rapidly proliferate and differentiate and, together with the allantois and chorion, form the haemochorial placenta. Although many of the uterine processes, both pre- and post-implantation, are under the regulation of female sex steroid hormones, the ubiquity of growth factors in the regulation of cell proliferation and differentiation in other systems (Metcalf, 1989), coupled with experiments largely with steroid responsive cells in culture (Sirbasku, 1978; Ikeda & Sirbasku,

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Jason G Knott and Soumen Paul

Mammalian reproduction is critically dependent on the trophoblast cell lineage, which assures proper establishment of maternal–fetal interactions during pregnancy. Specification of trophoblast cell lineage begins with the development of the trophectoderm (TE) in preimplantation embryos. Subsequently, other trophoblast cell types arise with the progression of pregnancy. Studies with transgenic animal models as well as trophoblast stem/progenitor cells have implicated distinct transcriptional and epigenetic regulators in trophoblast lineage development. This review focuses on our current understanding of transcriptional and epigenetic mechanisms regulating specification, determination, maintenance and differentiation of trophoblast cells.

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R. M. Borland, J. D. Biggers and C. P. Lechene

The large expansion of the rabbit blastocyst between the 3rd and 7th day post coitum(p.c.) is due to the accumulation of fluid in the blastocoele cavity (Daniel, 1964). Na+, Cl and HCO3 appear to be actively transported across the trophectoderm into the blastocoele (Cross, 1973, 1974) and water moves passively secondary to NaCl accumulation (Borland, Biggers & Lechene, 1976; see also review by Borland, 1977). The trophoblast cell is physiologically polarized in that Na is transported into the blastocoele by Na/K pumps (Na+–K+ ATPase, E.C. 3.6.1.3) located on the juxtacoelic plasma membrane of the trophoblast cells (Biggers, Borland & Lechene, 1977). This functional polarity is also reflected by the anatomical polarity of the trophectoderm. Membrane junctional complexes are located at the apices of the trophoblast cell and are adjacent to fluid-filled intercellular spaces that face the blastocoele cavity (Gamow & Daniel, 1970; Enders, 1971; Hastings & Enders, 1975; Ducibella, Albertini, Anderson & Biggers, 1975). Diamond & Bossert (1967) have proposed that such closed-end channels may be the site of active solute transport that creates local standing osmotic gradients which cause water flow across epithelia.