Effect of the stiffness of bone substitutes on the biomechanical behaviour of femur for core decompression.

Core decompression is the most common procedure for treatment of the early stages of osteonecrosis of the femoral head. The purpose of this study was to compare the biomechanical performance of four different bone graft substitutes combined with core decompression. Subject-specific finite element models generated from computed tomography (CT) scan data were used for a comprehensive analysis. Two different contact conditions were simulated representing states of osseointegration at the interface. Our results showed that the use of a low-stiffness bone substitute did not increase the risk of femoral fracture in the early postoperative phase, but resulted in less micromotion and interfacial stresses than high-stiffness bone substitutes.

Experimental and computational studies on the femoral fracture risk for advanced core decompression.

BACKGROUND: Two questions are often addressed by orthopedists relating to core decompression procedure: 1) Is the core decompression procedure associated with a considerable lack of structural support of the bone? and 2) Is there an optimal region for the surgical entrance point for which the fracture risk would be lowest? As bioresorbable bone substitutes become more and more common and core decompression has been described in combination with them, the current study takes this into account. METHODS: Finite element model of a femur treated by core decompression with bone substitute was simulated and analyzed. In-vitro compression testing of femora was used to confirm finite element results. FINDINGS: The results showed that for core decompression with standard drilling in combination with artificial bone substitute refilling, daily activities (normal walking and walking downstairs) are not risky for femoral fracture. The femoral fracture risk increased successively when the entrance point is located further distal. The critical value of the deviation of the entrance point to a more distal part is about 20mm. INTERPRETATION: The study findings demonstrate that optimal entrance point should locate on the proximal subtrochanteric region in order to reduce the subtrochanteric fracture risk. Furthermore the consistent results of finite element and in-vitro testing imply that the simulations are sufficient.

Influences of extracellular matrix and of conditioned media on differentiation and invasiveness of trophoblast stem cells.

Embryo implantation in the human and rodents relies on the trophoblast's ability to invade into the uterine stroma, partly depending on proteinases degrading components of basement membrane and underlying extracellular matrix (ECM). We have utilized mouse trophoblast stem (TS) cells (Science, 1998, 282:2072) to study trophoblast invasion and trophoblast-ECM interactions in vitro. On plastic in fibroblast-conditioned medium containing fibroblast growth factor (FGF)-4 and heparin, the cells remain proliferative but display increased differentiation in media without these components. Marker gene expression (Eomes, Pl-1, Tpbp) and invasion assays showed that TS cells exhibit increased invasive capacity when differentiating into giant cells and spongiotrophoblasts in unconditioned media without FGF-4 and heparin. Concomitantly, an up-regulation of matrix metalloproteinases (MMP)-9 and -14 was observed. Culture on gels of the basement membrane-like Matrigel resulted in striking changes in morphology and gene expression. Differentiating TS cells invaded into this ECM in a three-dimensional culture, while in turn ECM contact enhanced differentiation of TS cells and up-regulated the expression of MMP-9 and its tissue inhibitor (TIMP)-3. These findings implicate that the TS cell culture system used in this study can be utilized as a model for studying the regulation of trophoblast-ECM interactions, differentiation, and invasion in vitro.

Endometrial receptivity: selective adhesion competence of rabbit uterine epithelium for trophoblast but not for various tumor cells.

A modification of an established in vitro model for embryo implantation was used to probe the receptive uterine epithelium for any specificity of interaction with various invasive cells other than trophoblast. Endometrial explants consisting of stroma and epithelium taken from pseudopregnant rabbits were cultured in the presence of progesterone in order to regenerate a complete epithelial lining while maintaining the receptive state. Such precultured fragments were brought into contact with multicellular spheroids of different invasive tumor cell lines from different species. In contrast to the trophoblast of the rabbit blastocyst (previous publication), none of the tumor cell lines was able to adhere to intact epithelium of endometrial fragments nor to penetrate it. The uterine epithelium was also an insurmountable barrier for tumor cell spheroids confronted with the epithelium of fresh complex explants consisting of endometrium and myometrium or for spheroids introduced into the uterine lumen of pregnant/pseudopregnant rabbits at the periimplantation phase. However, all tumor cells were able to adhere to and mostly also to invade into the endometrial stroma when it was exposed artificially, i.e. when the epithelium was removed. These results suggest that the receptivity of rabbit uterine epithelium shows a remarkable selectivity with respect to cell type (trophoblast) and species (rabbit, not human, mouse, or rat).

Adhesion of trophoblast to uterine epithelium as related to the state of trophoblast differentiation: in vitro studies using cell lines.

At the initial phase of embryo implantation, the trophoblast must have acquired competence for adhesion to the uterine epithelium, a condition whose cell biological basis is far from understood. In the present study, trophoblast-type cells (BeWo, JAr, and Jeg-3 choriocarcinoma cell lines) were treated with retinoic acid, methotrexate, dibutyryl-cAMP, or phorbol-12-myristate-13-acetate in order to modulate their ability to adhere to uterine epithelial cells (RL95-2). In an established model, multicellular spheroids of choriocarcinoma cells were transferred onto the surface of monolayer cultures of RL95-2 cells followed by a centrifugal force-based adhesion assay. In controls, about 45% of BeWo and JAr cell spheroids and 75% of Jeg-3 spheroids adhered to uterine monolayers within 30 min. Pretreatment of spheroids with either of the agents stimulated differentiation as indicated by the rate of chorionic gonadotropin secretion, but consistently reduced the adhesion to the endometrial monolayer in all three choriocarcinoma cell lines. While previous investigations had shown that invasiveness of trophoblast cells (into extracellular matrix) does not seem to be linked to the differentiation program in a simple manner, the present data suggest that such an (inverse) link may indeed exist with respect to the ability to initiate an adhesive interaction with the uterine epithelium. These observations support the view that epithelial cell interactions as typical for the initial phase of embryo implantation are regulated in a way that is clearly different from cell-matrix interactions governing later phases of trophoblast invasion into the endometrial stroma.

[Low-dosage dental CT]. / Niedrigdosis Dental-CT.

PURPOSE: The intention of this study was to reduce patient dose during dental CT in the planning for osseointegrated implants. METHODS AND MATERIALS: Dental CTs were performed with a spiral CT (Somatom Plus 4, Siemens) and a dental software package. Use of the usual dental CT technique [1] (120 kVp; 165 mA, 1 s rotation time, 165 mAs; pitch factor 1) was compared with a new protocol (120 kVp; 50 mA; 0.7 s rotation time; 35 mAs; pitch factor 2) which delivered the best image quality at the lowest possible radiation dose, as tested in a preceding study. Image quality was analysed using a human anatomic head preparation. Four radiologists analysed the images independently. A Wilcoxon rank pair-test was used for statistic evaluation. The doses to the thyroid gland, the active bone marrow, the salivary glands, and the eye lens were determined in a tissue-equivalent phantom (Alderson-Rando Phantom) with lithium fluoride thermoluminescent dosimeters at the appropriate locations. RESULTS: By mAs reduction from 165 to 35 and using a pitch factor of 2, the radiation dose could be reduced by a factor of nine (max.) (e.g., the bone marrow dose could be reduced from 23.6 mSv to 2.9 mSv, eye lens from 0.5 mSv to 0.3 mSv, thyroid gland from 2.5 mSv to 0.5 mSv, parotid glands from 2.3 mSv to 0.4 mSv). The dose reduction did not lead to an actual loss of image quality or diagnostic information. CONCLUSION: A considerable dose reduction without loss of diagnostic information is achievable in dental CT. Dose-reducing examination protocols like the one presented may further expand the use of preoperative dental CT.

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.

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.

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.

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.

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.

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.

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.

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.

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.

Modulation of differentiation markers in human choriocarcinoma cells by extracellular matrix: on the role of a three-dimensional matrix structure.

During spontaneous or chemically induced differentiation human choriocarcinoma cells express typical characteristics of the normal differentiating trophoblast: 1) increased production of peptide and steroid hormones (chorionic gonadotropin, placental lactogen, estrogens, progesterone); 2) increased activity of cellular alkaline phosphatase; 3) morphological transition from cytotrophoblast to syncytiotrophoblast-like cells; and 4) arrested cell proliferation. Since the extracellular matrix is known to control gene expression we have examined the effects of different substrates composed of matrix macromolecules on the differentiation of BeWo choriocarcinoma cells. Matrices tested were: fibronectin, laminin, collagens type I and type IV, the basement membrane-like complex matrix Matrigel, and a complex matrix extracted from human term placenta. Irrespective of the type of molecule(s), it was consistently found that, whenever the matrix molecules were presented as three-dimensional structures (as opposed to protein coatings on tissue culture plastic) the response of affected differentiation markers monitored was highly pronounced. Morphology was changed from monolayers to rounded colonies, cell proliferation was reduced, and the secretion of chorionic gonadotropin was increased up to tenfold. Heterogeneous effects were observed on progesterone secretion and on the activity of cellular alkaline phosphatase. Cell adhesion to matrix molecules, however, did not depend on the structure of the matrix. This study demonstrates that gene expression in these tumor cells can be modified by extracellular matrix and highlights that not only the presence of effector molecules in the matrix but also the three-dimensional structure of the matrix is important for the induction of differentiation.

Development of rabbit preimplantation blastocysts cultured with precultured endometrial tissue.

Endometrial fragments were explanted from pseudopregnant rabbits 4.5 days after injecting with human chorionic gonadotrophin and were precultured for 2 days in suspension culture in the presence of oestradiol and progesterone equivalent to concentrations in rabbit serum at that stage. Preimplantation blastocysts were obtained at day 6.5 of pregnancy and cultured in the presence or absence of precultured endometrial fragments. Attachment of the trophoblast to the endometrium was prevented by continuous agitation. After 2 and 3 days, specimens were monitored for development in vitro using light and scanning electron microscopy. Although the development of blastocysts was slower in vitro than in vivo in both groups, development was clearly superior in the presence of precultured synchronous endometrial fragments. In the absence of endometrium, the embryonic anlage appeared disordered, particularly in the caudal region, but in the presence of uterine tissue the blastocysts developed much better. Up to nine somites were differentiated; the neural tube had started to close and the various parts of the brain anlage showed incipient differentiation. Syncytiotrophoblast differentiated in the presence or absence of endometrium in the embryonic and abembryonic hemispheres, but typical patterns were maintained better and cell degeneration was less frequent during co-culture. Although the culture model described here has not been optimized using criteria of blastocyst differentiation, the results suggest that culture of blastocysts with precultured synchronous endometrial fragments is advantageous.

Molecular cloning of a novel hyaluronan receptor that mediates tumor cell motility.

A cDNA encoding a unique hyaluronan receptor has been molecularly cloned from a lambda GT11 3T3 cDNA expression library. Immunoblot analyses of cell lysates, using antibodies to peptides encoded in the cDNA, specifically react with a 58-kD protein. This protein is regulated by the mutant H-ras gene in cells containing a metallothionein promoter H-ras hybrid gene. Further, antibodies to peptide sequences encoded in the cDNA block the increase in locomotion resulting from induction of the mutant H-ras gene in this cell line. In a transblot assay, the bacterially expressed protein binds to biotinylated hyaluronan. Antibodies to peptides encoded in the cDNA react in immunoblot assays with the 58- and 52-kD proteins of a novel hyaluronan receptor complex previously implicated in cell locomotion. Furthermore, antibodies specific to the 58- and 52-kD proteins, which block ras-induced locomotion, also cross-react with the expressed, encoded protein. The gene product described here appears to be a new type of hyaluronan receptor that is involved in cell locomotion. It is named RHAMM, an acronym for receptor for hyaluronan-mediated motility.

Rabbit endometrium in organ culture: morphological evidence for progestational differentiation in vitro.

This communication describes conditions for long-term organotypic culture of rabbit endometrium allowing progesterone-induced transformation, as typical for early pregnancy, to continue in vitro. This system appears to compare favorably with in vitro models so far proposed for the study of hormonal control of uterine function or for the investigation of cell-biological aspects of embryo implantation. The specific aim in the presented system is to provide approximate normal epithelium-stroma interrelationships. Fragments of endometrium consisting of epithelium and stroma were obtained during early pseudopregnancy and cultured on a gyratory shaker. Morphology was investigated by light microscopy, transmission and scanning electron microscopy. During the first two days the epithelium grows over the exposed stroma regenerating a complete epithelial lining. No central necrosis is found in the stroma for up to 6 days, and the tissue keeps its organotypic architecture although certain morphological differences can be observed between regenerated versus original epithelium. In the regenerating portion a stage-specific cell differentiation and the reformation of a basal lamina are missing. Progesterone substitution preserves cell morphology and allows to maintain, in vitro, the stage-specific pattern of cell organelles. Most characteristic is the induction of extensive fusion of epithelial cells. These large symplasms are comparable in size and structure to those formed in pregnancy in the implantation chamber in vivo. Only the superficial parts of the original (not the regenerated) epithelium are capable of progesterone-induced large-scale fusion. This organotypical culture system appears to be of potential value for in vitro studies on hormone action and on endometrial receptivity for embryo implantation.