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H W Denker

Publications and source records attributed to H W Denker.

At least 19 recordsLinked to original sources
PubMed1998

Differentiation markers and invasiveness: discordant regulation in normal trophoblast and choriocarcinoma cells.

In tumor cells, malignant (invasive) behavior and differentiation tend to be correlated inversely, although it is not clear to what extent this can be generalized and whether it may also apply to normal invasive cell types. We have modulated differentiation of normal trophoblast cells from first trimester or term placenta as well as choriocarcinoma cells (BeWo, Jeg-3, and JAr) with retinoic acid (RA), methotrexate (MTX), dibutyryl-cAMP (dbcAMP), or phorbol-[12-myristoyl-13-acetyl]-diester (PMA). The secretion of the differentiation marker chorionic gonadotrophin was stimulated by nearly all substances in all cell types. The activity of cellular sterylsulfatase showed a tendency to be increased (decreased by RA and dbcAMP in normal trophoblast; not detected in JAr). Invasiveness was decreased by all effectors in normal trophoblast (both types) and in BeWo. In Jeg-3 and JAr, however, PMA treatment (in JAr also RA treatment) increased invasion rates. These results suggest that only in normal trophoblast and in BeWo (but not in other choriocarcinoma cells, i.e., Jeg-3 and JAr) invasiveness and differentiation tend to be correlated inversely. When extrapolating to the various subpopulations of cells within a tumor, induction of differentiation-as intended in certain strategies for tumor therapy ("differentiation therapy")-may have the unwanted effect of stimulating invasiveness in certain subpopulations of tumor cells.

Antigens, Differentiation↗
PubMed1998

Identification of differentially expressed genes in human trophoblast cells by differential-display RT-PCR.

Molecular mechanisms controlling human trophoblast invasiveness are still poorly understood. In the present investigation, mRNA patterns of trophoblast cells isolated from first trimester (high invasiveness) and term placentae (no/low invasiveness) were compared by differential-display reverse transcriptase polymerase chain reaction (DDRT-PCR) revealing differential expression of numerous genes. Of 18 differentially expressed DDRT-PCR products analysed, 11 were unknown, four showed homologies with expressed sequence tag sequences, and three others were homologous to integrin-beta1, ATP-synthetase U6 (both showing higher expression in first trimester) or to aldose-reductase (higher expression at term), respectively. One of the unknown transcripts (PBK1, accession number: AJ007398) was cloned from a first trimester placenta cDNA library and was characterized. The 1908-bp gene fragment contains an open reading frame of 1551 bp and an Alu-sequence in the 3' non-coding region. According to Northern blot analysis on JAr choriocarcinoma cells, the fragment is close to full-length cDNA. By in situ hybridization, PBK1 was detected only in first trimester but not term placentae in the proximal parts of cell islands and in closely adjacent villous cytotrophoblast. This expression pattern suggests that the newly identified molecule, PBK1, could be involved in the regulation of proliferation/ differentiation and potentially in invasion of trophoblast cells.

ATP Synthetase Complexes↗
PubMed1998

Interactions between trophoblast and uterine epithelium: monitoring of adhesive forces.

At embryo implantation, it is postulated that the initial contact between blastocyst and maternal tissues is by adhesion of the trophoblast to the uterine epithelium. This cell-to-cell interaction is thought to be critical for implantation, although the actual adhesive forces have never been determined. In the present study, the atomic force microscope (AFM) was used to study the adhesion between human uterine epithelial cell lines (HEC-1-A; RL95-2) and human trophoblast-type cells (JAR). Specific interaction forces of these epithelia via their apical cell poles were determined on the basis of approach-and-separation cycles. For this purpose, the AFM tip was functionalized with JAR cells, then brought to the surface of uterine epithelial monolayers and was kept in contact for different periods of time (ms, 1, 10, 20, 40 min). The approach force curves displayed repulsive interactions for both HEC-1-A and RL95-2 cells. However, RL95-2 cells (with a smooth surface structure and a thin glycocalyx) showed lower values of the repulsive regime than HEC-1-A cells (with a rough surface structure and a thick glycocalyx). After having overcome repulsive interactions, the initial contact was followed by adhesive interactions. For contact times of 20 and 40 min, RL95-2 cells, but not HEC-1-A cells, showed specific JAR binding, i.e. the separation force curves displayed repeated rupture events in the range of 1-3 nN with a distance between 7-15 microm and, thereafter, a final rupture event at a distance of up to 45 microm. These features point to the formation of strong cell-to-cell bonds. Collectively, these studies provide the first definition of interaction forces between the trophoblast and the uterine epithelium, and are consistent with the hypothesis that an RL95-2-like architecture of uterine epithelial cells, i.e. an non-polarized phenotype, is essential for apical adhesiveness for the human trophoblast.

Cell Adhesion↗
PubMed1997

Adhesiveness of the free surface of a human endometrial monolayer for trophoblast as related to actin cytoskeleton.

Adhesiveness of the apical (free) plasma membrane of uterine epithelial cells for trophoblast is essential for the process of human embryo implantation. As epithelial cells are normally repellent, i.e. apically non-adhesive, we argue that a remodelling of the epithelial organization from a polarized to a non-polarized phenotype might prepare the apical pole for cell-cell adhesion during the so-called receptive phase. To identify details of apical adhesiveness we examined human epithelial RL95-2 cells (RL cells) which, in contrast to other cell lines, allow trophoblast to adhere to their apical plasma membrane. To determine whether the cytoskeletal structure is functionally critical for adhesiveness for trophoblast, RL cells were treated with actin depolymerizing cytochalasin D, i.e. 0.4 microM for 120 min. Changes in adhesiveness for trophoblast were monitored with a centrifugal force-based adhesion assay. Moreover, ultrastructural features, organization of the actin network and expression of integrins, i.e. alpha 6, beta 1, beta 4, were studied using electron microscopy, confocal laser scanning microscopy and cell surface immunogold-labelling techniques. Changes in transmission of mechanical signals via integrins into uterine cells were examined using a magnetic drag force device, thereby monitoring intracellular calcium responses. The results suggest that adhesiveness of the free surface of RL cells for human trophoblast requires an intact but non-polarized actin cytoskeleton, apically localized integrins linked to actin, and calcium signalling originating at the free surface.

Actins↗
PubMed1997

A hypermedia tutorial for cross-sectional anatomy: HyperMed.

Modern imaging techniques like computer tomography (CT) and nuclear magnetic resonance (MR) imaging have become essential in clinical diagnostics and also in teaching gross anatomy to medical students. As a consequence, special classes in (cross)-sectional anatomy are being added to the curriculum in many anatomical institutions. Since institutional budgets often do not allow extensive supervision beyond the very limited time frame of traditional courses in gross anatomy, a computer-based hypermedia tutorial (HyperMed) was created and integrated into the teaching program of the Institute of Anatomy at Essen University. HyperMed offers two components, one for authors (e.g. teachers who can customize the contents of the program) and a second for users (e.g. students). In the present version, digital cross-sectional human images have been edited. The relevant anatomical structures in these images have been marked, named, and linked to additional information and figures (in particular schematic figures and CT images). Users can obtain information at different levels: (1) index-based retrieval, (2) navigational retrieval (on inspecting cross-sectional images the user is asked to identify structures) and (3) a history list enabling users to go back to any previous point of navigation. HyperMed was first tested in the winter terms 1995/1996 and 1996/1997 during classes on cross-sectional anatomy which are a supplement to the traditional dissection course of the Institute of Anatomy, University Essen. It was well received by the students who found it a helpful adjunct to learning cross-sectional anatomy.

Anatomy, Cross-Sectional↗
PubMed1997

Neoglycoprotein-binding sites (endogenous lectins) in the Fallopian tube, uterus and blastocyst of the rabbit during the preimplantation phase and implantation.

Regulation of the initial phase of embryo implantation may involve the recognition interplay of glycoconjugates and respective receptors such as endogenous lectins on both cellular surfaces. Whereas changes in glycoconjugate composition have been detected in preparation for embryo implantation and described in detail, knowledge on endogenous lectins has remained scant. Affinity probes (carrier-immobilized carbohydrate structures as ligand part on a histochemically inert backbone) are used in the present investigation in order to gain further insights in this area. Cryostat sections of rabbit Fallopian tubes and uteri in nonpregnant and early pregnant [tubes: 3 days post coitum (d p.c.); uteri: 3, 5, 7 and 9 d p.c.] states were studied for binding patterns of a series of biotinylated (neo)glycoproteins. A high density of binding sites was detected with beta-galactosides (with decreasing intensity: beta-D-galactose-BSA, asialofetuin with its triantennary glycan chains, lactose-BSA). Considerably less binding (but with the same pattern) was obtained with beta-N-acetyl-D-glucosaminide-BSA and is interpreted to originate from a cross-reactivity of such sites which may bind physiologically to Gal-beta1,3/4-GlcNAc sequences. In contrast, no evidence for the presence of binding molecules with specificities for a-D-mannose-BSA, maltose-BSA, N-acetyl-galactosaminide-BSA and N-acetyl-D-neuraminic acid-BSA was obtained in these tissues under the same conditions. The epithelium of the Fallopian tube showed a high density of beta-galactoside-binding sites at the apical cell poles (including the cytoplasm and membrane region) already in the nonpregnant state. At 3 d p.c., a strong reaction in all epithelial cells of the isthmus and a marked decrease in the ampulla were noted. The putative lectin(s) appear(s) to be synthesized and secreted by the tubal epithelium. A physiological role in forming the mucoprotein layer of the blastocyst coverings by precipitating the appropriate mucin-type molecules can be considered. Within the endometrium, the beta-galactoside-binding molecules were almost exclusively localized at the apical cell pole of epithelial cells, whereas there was hardly any binding in the epithelial cytoplasm or in the endometrial stroma. The reaction was very weak in the non-pregnant state but increased considerably until 5 d p.c., starting in the luminal-most parts of the epithelium. While the reaction was rather homogeneous at the surface of the luminal epithelium at 5 d p.c., the degree of heterogeneity increased stepwise from 7 to 9 d p.c. In the implantation chamber, the density of these beta-galactoside-specific 'receptors' was further enhanced in particular at the epithelial surface of the placental folds. In contrast, the reaction was less intense at the antimesometrial uterine epithelium and in interblastocyst segments of the uterus, and it remained weak in the middle and deep crypts. The trophoblast showed a high density of galactoside-binding sites at its surface, and less in the cytoplasm. Neoglycoprotein binding to the blastocyst coverings observed at 7 d p.c. was strong in particular at the outer and inner surfaces. Physical factors (e.g. differential texture at surfaces) are discussed to influence the staining patterns of these extracellular coverings. Nevertheless, the observations made on the tubal and the uterine mucosa suggest that the putative lectin(s) detected here is (are) secreted by these epithelia and could be involved in the structural organization of the various layers of the blastocyst coverings with their remarkable content of oligosaccharide chains. This effect on topological aspects of the zona pellucida equivalents may be important for the interplay between trophoblast and uterine epithelium and the cascade leading to implantation initiation.

Animals↗
PubMed1996

Epithelial cell polarity and embryo implantation in mammals.

At embryo implantation we are confronted with the fact that uterine and trophoblast epithelium make contact via their apical cell membranes. This epithelium-epithelium adhesion leading to definitive attachment of the embryo to the uterine wall, however, is far from being trivial and has been called a cell biological paradox. It has been proposed that some of the molecular events involved in epithelium-to-mesenchyme transformation might play a role in the interaction between uterine cells and trophoblast. As a mechanism to achieve uterine epithelium adhesiveness for trophoblast it is postulated that uterine cells partially modulate their epithelial phenotype. Data from recent in vitro experiments give support to this hypothesis and suggest that loss of apical-basal cell polarity might prepare the apical cell pole of uterine epithelium for cell-to-cell contact with trophoblast in vivo.

Animals↗
PubMed1996

The role of matrix contact and of cell-cell interactions in choriocarcinoma cell differentiation.

Cell differentiation is supported much better by gels of extracellular matrix than by the same matrix provided as a rigid substrate. Many cell types including normal and malignant trophoblast cells, however, form multicellular multilayered aggregates on matrix gels with increased cell-to-cell contacts as compared to regular monolayers on rigid matrix substrates. In such cultures, it remained open, so far, whether stimulated expression of differentiation markers is caused by enhanced cell-to-cell communication or is displayed only by cells in direct contact to the gel. Therefore, choriocarcinoma cells (BeWo) were grown as aggregates: (a) on gels of the basement membrane-like Matrigel, (b) on plastic coated with poly-HEMA, or (c) as aggregates (spheroids) in suspension culture. Production of the differentiation marker chorionic gonadotropin was stimulated significantly in aggregates attached to gels of Matrigel or to the poly-HEMA substrate but not in suspended spheroids. With respect to cell-cell communications, however, expression of E-cadherin mRNA was not altered in any type of aggregates, as compared to control cultures on plastic. The expression of connexin43 mRNA (not of connexin26) was increased only in suspended spheroids, while microinjection of the fluorescent dye Lucifer Yellow suggested that cell communication via gap junctions was absent from cells grown as monolayers and was not induced in any type of aggregate. When cells were grown on gels of Matrigel, the relevance of direct cellular contact to the substrate for differentiation was analyzed by immunohistochemistry. Trophoblastic differentiation markers (chorionic gonadotropin, placental lactogen, placenta-type alkaline phosphatase, and pregnancy-specific glycoprotein beta 1) as well as the proliferation marker Ki-67 were not preferentially expressed in cells that were in contact with the gel. Similar random distributions of all these markers were also observed in spheroids cultured in suspension. The distributions of several matrix molecules and of different integrins were comparable between aggregates on matrix gels and those in suspension culture. According to these data, cell-cell communication appears to play a subordinate role for cytodifferentiation in cell aggregates on matrix gels, so that substrate anchorage and physical properties of the substrate may be the decisive factors. Interestingly, however, direct contact to the substrate does not seem to be essential for the stimulation of differentiation in cells on matrix gels. The results are discussed in the context of the "tensegrity"-model for cell-matrix interactions in which proper mechanical properties of the substrate are important for the regulation of cell differentiation by allowing a balanced integrity of external and cell-internal tensile forces.

Actins↗
PubMed1996

Adhesiveness of the apical surface of uterine epithelial cells: the role of junctional complex integrity.

Embryo implantation necessitates that the apical plasma membrane of uterine epithelial cells acquires adhesiveness. Recent studies have indicated that modulation of a major element of the epithelial phenotype, i.e. apical-basal cell polarity, might be critical in this respect. Here, we analyze polar characteristics of nonadhesive vs. adhesive uterine epithelial cell lines focusing on cytoskeletal-junctional interactions that may play a role in regulating adhesiveness of the apical plasma membrane. HEC-1-A is a human uterine epithelial cell line exhibiting nonadhesive properties of its apical surface for trophoblast, whereas RL95-2 represent another such cell line exhibiting adhesive properties enabling trophoblast attachment. Homotypic intercellular contacts and functionally related proteins, i.e. ZO-1, E-cadherin, alpha-catenin, beta-catenin, plakoglobin, and desmoplakin 1, were examined by transmission electron microscopy, immunocytochemistry, confocal laser scanning microscopy, and immunoprecipitation techniques. In addition, details of actin filament architecture were studied after phalloidin labeling. While nonadhesive HEC-1-A exhibited the well-known pattern of cell-to-cell contacts of polarized epithelial cells, adhesive RL95-2 showed a lack of ZO-1 expression, tracer leakiness of the paracellular pathway, and atypical features in adherens junctions: E-cadherin, alpha-catenin and plakoglobin were colocalized in all plasma membrane domains and beta-catenin was localized in lateral membrane domains. Immunoprecipitations showed in both cell lines the presence of two different E-cadherin-catenin complexes, one composed of E-cadherin, alpha-catenin and beta-catenin, and the other of E-cadherin, alpha-catenin and plakoglobin. Concerning RL95-2 these data indicate that E-cadherin/plakoglobin complexes are randomly distributed, whereas E-cadherin/beta-catenin complexes are laterally localized in these cells. Additionally, the actin-based cytoskeleton of RL95-2 lacked a polar organization. With respect to the intermediate filament-desmosome system, both cell types expressed desmoplakin I, but the vast majority of RL95-2 lacked well-formed desmosomes as demonstrated by electron microscopy. It is concluded that modulation of tight junctions and/or remodelling of adherens junctions, e.g. differential distribution of E-cadherin/plakoglobin complexes and E-cadherin/beta-catenin complexes, are correlated with the development of apical adhesiveness of human uterine epithelial cells. This model system should allow to test experimentally whether this correlation is due to any causal function in the development of epithelial cell polarity.

Actins↗
PubMed1995

A novel artificial substrate for cell culture: effects of substrate flexibility/malleability on cell growth and morphology.

Gels of glyoxyl agarose (GA) are evaluated as a novel flexible substrate for cell culture with physical properties comparable to extracellular matrix (ECM) gels. We show here that cells adhere well to pure GA gels; in addition, specific interactions involving matrix receptors can be studied when individual matrix molecules are bound to the gel covalently. When cells are grown on such substrates, morphology is comparable to that observed on "natural" matrix gels (reconstituted gels of collagen type I or of Matrigel): rather than being flattened as in monolayer cultures on tissue culture plastic the cells assume a rounded morphology and tend to form tissue-like aggregates. The effects of the artificial matrix gels are discussed in the context of previous publications on cell interactions with the extracellular matrix, suggesting that in addition to specific recognition of matrix molecules the physical properties of ECM by themselves can be decisive for cell differentiation. We conclude that gels of glyoxyl agarose a) provide a useful model to mimic the physical properties of matrix gels without the presence of specific adhesion factors; b) may be useful as a general, non-specific ECM allowing cells to be cultured in vitro under conditions favorable for differentiation; and c) allow to design a variety of "synthetic" ECM models composed of a chemically defined gel matrix, which can be supplemented with covalently bound molecules to be recognized by cell surface receptors.

Cell Adhesion↗
PubMed1995

Differential expression of CD44 in rabbit uterine epithelium during early pregnancy.

The expression of the cell surface glycoprotein CD44 was monitored in rabbit endometrium during early pregnancy and pseudopregnancy by immunohistochemistry. The epitope was not detected in the uterine epithelium of nonpregnant doses; in pseudopregnant animals it was expressed only weakly and late, most clearly detectable at the last stage investigated, i.e. on day 10. During pregnancy, however, CD44 was expressed more strongly in the epithelium starting on day 6, i.e. shortly before embryo implantation (day 7). Northern blot analysis confirmed this increase in expression. Immunohistochemically, CD44 expression peaked around days 8 and 9 of pregnancy and was generally localized on the lateral cell membranes of uterine epithelium, but not on basal or apical membranes. The staining pattern was similar on all major mucosal folds in that the signal was most intense in the luminalmost parts and slightly less in the middle of these folds. The intensity was gradually reduced towards the depth of the crypts with their deepest parts being negative. At day 10 of pregnancy the intensity of staining was clearly reduced in all parts of the epithelium that had been positive before. Fusion of epithelial cells, a characteristic phenomenon in pregnant rabbit uteri, which is particularly widespread in the implantation chamber, was accompanied with abolishment of CD44 expression. While stromal cells in general showed only a weak reaction, some individual cells in the stroma were always strongly positive (numbers increased after implantation). The trophoblast only occasionally exhibited some faint cellular staining in cytotrophoblast as well as in syncytiotrophoblast. These data show that CD44 is expressed in rabbit uterine epithelium during the periimplantation phase, and that its expression appears to be triggered by embryonic signalling and may be relevant for implantation.

Animals↗
PubMed1995

Differential expression and localization of integrins and CD44 in the membrane domains of human uterine epithelial cells during the menstrual cycle.

Human uterine epithelium displays a distinctly polarized organization with basal, lateral, and apical plasma membrane domains. Although nonadhesive throughout most of the menstrual cycle, uterine epithelial cells allow attachment of trophoblast cells to their apical pole during embryo implantation. Development of the receptive state might involve expression of cell adhesion molecules and/or redistribution of such molecules with respect to their localization at the basal, lateral, and apical membrane domains of cells. Expression and distribution of alpha 1-, alpha 3-, alpha 5-, alpha 6-, beta one-, beta 3- and beta 4-integrin subunits as well as of CD44 were examined in the luminal epithelium of human endometrium by immunohistochemistry in different phases of the menstrual cycle. The luminal epithelium was found to express alpha 1-, alpha 3-, alpha 6-, beta 1-, beta 4-integrin subunits and CD44. alpha l6-Integrin subunits and CD44 displayed cycle dependency. The alpha 6-integrin subunits were detected in the basal membrane domains in all phases. However, in correlation with increasing expression during the secretory phase of cycle, these subunits newly appeared in the lateral membranes of epithelial cells. CD44 showed increased expression in the secretory phase but was always restricted to the lateral membranes. The conspicuous behavior of alpha 6-integrin subunits and CD44 is discussed with respect to its possible functional significance for embryo implantation, and in relation to a hypothesis postulating that steroid-controlled master genes direct the acquisition of the receptive state of the luminal uterine epithelium by changing elements of the apicobasal polarity of these cells.

Endometrium↗
PubMed1995

Cell adhesion to the apical pole of epithelium: a function of cell polarity.

Human uterine epithelium displays a distinct polarized organization with apical, lateral, and basal plasma membrane domains. Although non-adhesive throughout most of the menstrual cycle, epithelial cells allow attachment of trophoblast cells to their apical pole during embryo implantation. A recent hypothesis postulates that epithelial cells turn off genes for apical-basal polarity and turn on genes for a more mesenchyme-like phenotype allowing cell-cell interaction with trophoblast. Using an in vitro assay human uterine cell lines (RL95-2, HEC-1-A, AN3-CA) were selected on the basis of adhesiveness for trophoblast-type cells (JAR). Subsequently, uterine cells were examined for epithelium-specific ultrastructure using transmission electron microscopy, and for the expression of E-cadherin, alpha 6-, beta 1-, beta 4-integrin subunits and cytokeratin using immunocytochemistry, confocal laser scanning microscopy, and surface replication technique. HEC-1-A monolayers are non-adhesive for JAR cells and appear highly polarized expressing E-cadherin, alpha 6-, beta 1-, beta 4-integrin subunits, and cytokeratin. Both, integrins and E-cadherin, are present at the lateral membrane. RL95-2 monolayers which are adhesive for JAR cells appear non-polarized. Like HEC-1-A cells, RL95-2 cells express E-cadherin, alpha 6-, beta 1-, and beta 4-integrin subunits, and cytokeratin. In contrast to HEC-1-A cells, integrins and E-cadherin are distributed at the entire cell surface. AN3-CA monolayers are non-adhesive for JAR cells and appear non-polarized. Cells lack epithelial-specific markers such as keratin and E-cadherin. They show only low expression of alpha 6-, beta 1-integrin subunits and lack beta 4-integrin subunit. Conversely, they express vimentin. Thus, modulation of the epithelial phenotype of uterine cells, i.e. loss of apical-basal polarity, might prepare the apical cell pole for cell-cell interaction with trophoblast. However, loss of cell polarity would not lead to enhancement of adhesiveness for trophoblast if accompanied by a loss of epithelium-specific adhesion molecules.

Cadherins↗
PubMed1994

The role of cell shape for differentiation of choriocarcinoma cells on extracellular matrix.

The role of extracellular matrix (ECM) in directing cell differentiation has been interpreted so far predominantly in terms of chemical signaling from individual matrix molecules. Recent data, however, suggest that the physical properties of ECM contribute signals for differentiation, which can be decisive and possibly even more important than chemical composition. In the present investigation, effects of different artificial matrices on the differentiation of BeWo choriocarcinoma cells were studied systematically. In Series (a) cells were grown on nonspecifically adhesive substrate gels (gels of glyoxyl agarose with or without poly-L-lysine crosslinked to) and on artificial matrix gels (matrix molecules covalently bound to agarose gels). Differentiation in terms of chorionic gonadotropin (hCG) secretion was stimulated on all artificial gel substrates much more than on rigid substrates of the same chemical composition. Concomitantly a change in morphology was observed to a rounded shape of cells in aggregates attached to the substrate. A series (b) of substrates with gradually reduced adhesiveness was created by coating plastic with different concentrations of poly-HEMA. In this sequence, gradual changes in cell morphology (stepwise approximation to a spherical shape) correlated with increased hCG secretion comparable to that on matrix gels. In contrast, in aggregates kept in suspension the increase in secretion of hCG was only marginal. These results clearly support that in addition to chemical recognition of individual matrix molecules, cells respond strongly to physical properties of extracellular matrix and that the physics of interaction of cytoskeleton, cell surface, and ECM can become decisive for cell differentiation.

Animals↗
PubMed1994

Adhesion and invasion of three human choriocarcinoma cell lines into human endometrium in a three-dimensional organ culture system.

A novel in vitro model was developed to study attachment and invasion of choriocarcinoma cell spheroids using pre-cultured secretory phase human endometrium as a host tissue. During pre-culturing in shaker culture human endometrium had regenerated a complete epithelial covering and had shed cells damaged during explantation. Spheroids of three human choriocarcinoma cell lines (BeWo, Jeg-3, JAr) which displayed linear growth in culture and produced placental hormones were used in this study as models for trophoblast behaviour. Morphological differences were noted in the spheroids from the three choriocarcinoma cell lines; BeWo and Jeg-3 spheroids exposed flattened and more differentiated cells on their surfaces while superficial cells in JAr spheroids maintained their cytotrophoblast-like morphology. Spheroids from all three cell lines were proven to be invasive in a general invasion assay using embryonic chick heart fragments, with JAr spheroids being the most aggressive. When spheroids were confronted with pre-cultured re-epithelialized endometrial fragments, however, Jeg-3 spheroids showed the highest incidence of attachment (52%) and the greatest amount of invasion into the underlying stroma. BeWo spheroids also attached (37%) and penetrated the epithelium, but did not invade into the stroma. JAr spheroids showed a minor degree of attachment (12%) and little or no invasion into the stroma. These results show that the three choriocarcinoma cell lines, although all invasive in a general invasion assay, differ in adhesion to uterine epithelium and invasion into endometrial stroma. This model offers opportunities for studying mechanisms of trophoblast adhesion and invasion, using human endometrium as the natural host tissue.

Animals↗
PubMed1993

Implantation: a cell biological paradox.

Implantation initiation in eutherian mammals requires, at least in invasive types of implantation, that 1) the trophoblast or subpopulations of it have reached a state of "invasiveness" and, synchronously, 2) the endometrium has reached a state of "receptivity" ("implantation window"). The cell biological basis of "receptivity" as well as of "invasiveness" has long remained unknown, but recently it appears that the application of modern concepts of cell and developmental biology is opening new views of it, concentrating on cell adhesion and cell polarity phenomena. Implantation initiation requires that the trophoblast attaches via its apical plasma membrane to the apical plasma membrane of the uterine epithelium. Since apical plasma membranes of epithelia are normally non-adhesive, this represents a cell biological paradox. In development, cells can express two major phenotypes and switch between these: 1) the mesenchymal/fibroblastoid phenotype that is compatible with cells moving individually; 2) the epithelioid phenotype which is characterized by cells expressing apico-basal polarity and a strong association with neighbouring cells via various junctions, so that they can migrate as sheets but not as individual cells. Application of this concept to embryo implantation would seem to lead to the hypothesis that the trophoblast of blastocysts has to give up part of its typical epithelial organization when becoming invasive; it must express cell-cell adhesion molecules or matrix receptors non-typically at its apical plasma membrane, change the spectrum of expressed adhesion molecules, and alter its motility apparatus. This applies in a somewhat similar way to the uterine epithelium at "receptivity". Interestingly, recent data show that a substantial number of differentiation parameters of these cells change in addition. It appears that part of the epithelial differentiation program is down-regulated at this phase. This also suggests interesting new aspects of the basis of steroid hormone action at the endometrium, as well as of trophoblast invasiveness, possibly involving switches in the activity of regulatory "master" genes as are also involved in decision making during development.

Animals↗