Stimulation of tenascin expression in mesenchyme by epithelial-mesenchymal interactions

Tenascin is an extracellular matrix glycoprotein with an unusually restricted tissue distribution in the developing embryo. The protein was independently discovered by several investigators, and has been given many different names. Synonyms of tenascin include cytotactin, J1, hexabrachion and glioma-mesenchymal extracellular matrix antigen. Whereas fibronectin is expressed rather uniformly in matrices of embryonic mesenchyme, tenascin is found in the mesenchyme at sites of epithelial-mesenchymal interactions. Tenascin is thus found close to epithelial basement membranes but it is probably not an integral basement membrane component. The distribution suggests that developing epithelial cells may produce locally active factors that stimulate tenascin synthesis in the nearby mesenchyme. Tenascin is composed of disulfide-bonded subunits of approximate Mr between 200-280 kD. Using monoclonal antibodies to mouse tenascin, we find two major subunits of Mr 260 and 200 kD from mouse fibroblasts. Work from many laboratories suggests that the different subunits arise by differential splicing of one mRNA. Rotary shadowing electron microscopy of the intact molecule suggests a six-armed structure connected by a central region. However, the different subunits are not co-ordinately expressed during embryogenesis, suggesting that tenascin can exist as different isoforms. The different isoforms may serve distinct functions. The function of tenascin is not well known, but it has been suggested that it alters the adhesive properties of cells and causes cell rounding.     

Epithelial induction of stromal tenascin in the mouse mammary gland: from embryogenesis to carcinogenesis

The distribution of the extracellular matrix glycoprotein tenascin was studied by immunofluorescence in the developmental history of the mouse mammary gland from embryogenesis to carcinogenesis. Tenascin appeared only in the mesenchyme immediately surrounding the epithelia just starting morphogenesis, that is, in embryonic mammary glands from 13th to 16th day of gestation, in mammary endbuds which are a characteristic structure starting development during maturation of the mammary gland, and in the stroma of malignant mammary tumors. However, tenascin was absent in the elongating ducts of embryonic, adult, proliferating, and involuting mammary glands and preneoplastic hyperplastic alveolar nodules. The transplantation of embryonic submandibular mesenchyme into adult mammary glands induces the development of duct-alveolus nodules, which morphologically resemble developing endbuds. Tenascin reappeared around those nodules during the initial stages of their development. Tenascin expression could be induced experimentally in several ways. First, tenascin was detected at the site where the first mammary tumor cells GMT-L metastasized. Second, tenascin was detected in the connective tissue in the tumors derived from the injected C3H mammary tumor cell line CMT315 into Balb/c nude mouse. Cross-strain marker anti-CSA antiserum clearly showed that the tenascin-positive fibroblasts were of Balb/c origin. Third, when embryonic mammary epithelium was explanted on to embryonic mammary fat pad cultures, the mesenchymal cells condensed immediately surrounding the epithelium. Tenascin was detected in these condensed cells. From these three observations we conclude that both embryonic and neoplastic epithelium induced tenascin synthesis in their surrounding mesenchyme.     

Changes in the distribution of tenascin during tooth development

Tenascin is an extracellular matrix molecule that was earlier shown to be enriched in embryonic mesenchyme surrounding the budding epithelium in various organs including the tooth. In the present study tenascin was localized by immunohistology throughout the course of tooth development in the mouse and rat using polyclonal antibodies against chick tenascin. The results indicate that tenascin is expressed by the lineage of dental mesenchymal cells throughout tooth ontogeny. The intensity of staining with tenascin antibodies in the dental papilla mesenchyme was temporarily reduced at cap stage when the tooth grows rapidly and undergoes extensive morphogenetic changes. During the bell stage of morphogenesis, the staining intensity increased and tenascin was accumulated in the dental pulp even after completion of crown development and eruption. Tenascin was present in the dental basement membrane at the time of odontoblast differentiation. The dental papilla cells ceased to express tenascin upon differentiation into odontoblasts and tenascin was completely absent from dentin. It can be speculated that the remarkable expression of tenascin in the dental mesenchymal cells as compared to other connective tissues is associated with their capacity to differentiate into hard-tissue-forming cells.     

Close correlation between the distribution of tenascin and that of actin filaments in the mouse urethral mesenchyme during active morphogenesis.

The distribution of tenascin, an extracellular matrix glycoprotein, and that of actin filaments were studied in the developing urethra of mouse embryos by antitenascin immunofluorescent and rhodamine-phalloidin staining. Tenascin appeared transiently in the urethral mesenchyme at the site of active morphogenesis in which the urethral epithelium separated from the surface epithelia of the glans and prepuce, being tubular, and the bilateral mesenchymes lining the preexisting urethral epithelium were seamed together in the ventral side of the tubular urethra immediately after the epithelial separation. The spatially and temporally restricted distribution of tenascin corresponded well to that of mesenchymal cells which possessed many actin filaments. These observations suggest that tenascin is involved in the cytoskeletal organization of mesenchymal cells in the active phase of morphogenesis.     

Sequential induction of syndecan, tenascin and cell proliferation associated with mesenchymal cell condensation during early tooth development

The cell surface proteoglycan, syndecan, and the extracellular matrix glycoprotein, tenascin, are expressed in the mesenchyme during early development of many organs. We have studied the expression patterns of syndecan and tenascin during initiation of tooth development and in association with mesenchymal cell condensation and compared these with cell proliferation. Syndecan, tenascin and bromodeoxyuridine (BrdU) incorporation were localized by triple-labelling immunohistochemistry in serial sections of molar tooth germs of mouse embryos. Prior to formation of the epithelial tooth bud, syndecan accumulated in the mesenchymal cells which underlie the presumptive dental epithelium, but tenascin was not detected at this stage. Tenascin appeared during initiation of the epithelial down-growth at the lingual aspect of the tooth germ. During subsequent formation of the epithelial bud, at the late bud stage, syndecan and tenascin became exactly colocalized in the condensed mesenchyme which was clearly demarcated from other jaw mesenchyme. The expression of syndecan and tenascin was accompanied by rapid cell proliferation as indicated by marked BrdU incorporation. When development advanced to the cap stage, syndecan staining intensity in the dental papilla mesenchyme increased further whereas tenascin became reduced. In conclusion, the results demonstrate that the expression patterns of syndecan and tenascin overlap transiently during the period of mesenchymal cell condensation and that this is accompanied by cell proliferation. Syndecan and tenascin may play a role in growth control and in compartmentalization of the dental mesenchymal cells in the condensate.     

Immunofluorescent localization of tenascin during development of the mouse urogenital sinus: Possible involvement in genital duct morphogenesis

Tenascin is a compound of the mesenchymal extracellular matrix and has been proposed as a possible mediator in epithelial-mesenchymal interactions, because of its characteristic distribution in tissues during fetal development. In the present study, we have investigated by immunofluorescence the changes in the distribution of tenascin during development of the mouse urogenital sinus, a process in which tissue interactions were found to be essential. Tenascin first appears in dorsal mesenchyme on days 13-15 of gestation, coinciding with morphological changes of the epithelium. During male development, tenascin accumulates in the dorsal mesenchyme around the junction of Wolffian ducts, but not in the ventral mesenchyme, into which prostatic buds (prostate gland anlagen) project from the sinus epithelium. During female development, the mesenchyme that participates in the downgrowth of the vagina (derived from Müllerian ducts) stains intensively for tenascin. In both of these tenascin-positive areas, the epithelium undergoes conspicuous morphogenetic changes. The results suggest that mesenchymal tenascin could be involved in the epithelial morphogenesis of the sinus, especially in the morphogenesis of the genital ducts.     

Epithelial-mesenchymal interactions in the developing kidney lead to expression of tenascin in the mesenchyme

Tenascin, a mesenchymal extracellular matrix glycoprotein, has been implicated in epithelial-mesenchymal interactions during fetal development (Chiquet-Ehrismann, R., E. J. Mackie, C. A. Pearson, T. Sakakura, 1986, Cell, 47:131-139). We have now investigated the expression of tenascin during embryonic development of the mouse kidney. In this system, mesenchymal cells convert into epithelial cells as a result of a tissue interaction. By immunofluorescence, tenascin could not be found in the mesenchyme until kidney tubule epithelial began to form. It then became detectable around condensates and s-shaped bodies, the early stages of tubulogenesis. In an in vitro culture system, tenascin expression by the mesenchyme is tightly coupled to the de novo formation of epithelial, and does not occur if tubulogenesis is suppressed. The results strongly suggest that the formation of the new epithelium stimulates the expression of tenascin in the nearby mesenchyme. During postnatal development, the expression of tenascin decreases and the spatial distribution changes. In kidneys from adult mice, no tenascin can be found in the cortex, but interspersed patches of staining are visible in the medullary stroma. The results strongly support the view that tenascin is involved in epithelial-mesenchymal interactions. It could therefore be crucial for embryonic development.     

Tenascin Expression in Vitro and in Vivo: Comparison between Epithelial and Nonepithelial Rat Cell Lines

Tenascin is a novel six-armed extracellular-matrix glycoprotein expressed in association with mesenchymal-epithelial interactions, and its expression is temporally and spatially restricted during organogenesis and carcinogenesis. The distribution and alterations in the expression of fibronectin, laminin, and especially of tenascin, were compared between in vitro and in vivo studies with rat epithelial (hepatocyte-derived) and nonepithelial (sarcoma-derived) cell lines. Immunoprecipitation studies revealed that the production of extracellular-matrix glycoproteins varied among the cell lines. Two ascites-hepatoma-derived cell lines and one sarcoma-derived line were found to synthesize tenascin in vitro. Their major tenascin isoform yielded a molecular weight of 220 kDa under reducing conditions. The other cell lines examined, including all of those derived from normal hepatocytes, were negative for the expression of tenascin. Coculture studies were performed between epithelial and nonepithelial cell lines. No drastic change in tenascin expression was found after coculturing the cells. As an in vivo study, cell lines were transplanted into nude mice. All xenografts of the epithelial lines were associated with a strong positive reaction for extracellular-matrix glycoproteins, and especially for tenasein, in the mouse fibrous stroma adjacent to them. This represents the epithelial induction of stromal tenascin. Whether or not they produced tenascin in vitro, after transplantation none of the epithelial cell lines themselves produced tenascin, whereas both of the nonepithelial cell lines prominently produced tenascin. These findings suggest that, in the process of interactions between epithelial and nonepithelial cells, the expression of tenascin depends on the switch from in vitro to in vivo.     

Gizzard epithelium of chick embryos can express embryonic pepsinogen antigen,a marker protein of proventriculus

Summary The avian stomach is composed of two distinct organs, the proventriculus and the gizzard. Pepsinogen expression in the proventricular and gizzard epithelia of chick embryos was investigated immunohistochemically with anti-embryonic chick pepsinogen (anti-ECPg) antiserum. In normal development, the ECPg antigen was expressed only in the glandular epithelial cells of the embryonic proventriculus from the 8th day of incubation onwards. However, both proventricular and gizzard epithelia of 6-day embryos expressed the ECPg antigen when recombined and cultured with the proventricular mesenchyme. Chronological studies revealed that the ECPg antigen was first detected in a few epithelial cells at 3 days of cultivation. The percentage of ECPg-positive cells among the total epithelial cells in each recombinant increased with the length of the culture period and all the glandular epithelial cells were positive at 9 days. During this process, the percentage of ECPg-positive cells in each cultured recombinant was similar in proventricular and gizzard epithelia. Moreover, both epithelia could express the ECPg antigen when recombined and cultured with the oesophageal or small-intestine mesenchyme for 9 days, though the percentage of ECPg-positive cells in each cultured recombinant was much lower than that in the cultured recombinant with the proventricular mesenchyme. These results indicate that the gizzard epithelium of 6-day chick embryos possesses a similar potential for pepsinogen expression as the proventricular epithelium of the same age.     

Envoplakin, a novel precursor of the cornified envelope that has homology to desmoplakin

The cornified envelope is a layer of transglutaminase cross-linked protein that is deposited under the plasma membrane of keratinocytes in the outermost layers of the epidermis. We present the sequence of one of the cornified envelope precursors, a protein with an apparent molecular mass of 210 kD. The 210-kD protein is translated from a 6.5- kb mRNA that is transcribed from a single copy gene. The mRNA was upregulated during suspension-induced terminal differentiation of cultured human keratinocytes. Like other envelope precursors, the 210- kD protein became insoluble in SDS and beta-mercaptoethanol on activation of transglutaminases in cultured keratinocytes. The protein was expressed in keratinizing and nonkeratinizing stratified squamous epithelia, but not in simple epithelia or nonepithelial cells. Immunofluorescence staining showed that in epidermal keratinocytes, both in vivo and in culture, the protein was upregulated during terminal differentiation and partially colocalized with desmosomal proteins. Immunogold EM confirmed the colocalization of the 210-kD protein and desmoplakin at desmosomes and on keratin filaments throughout the differentiated layers of the epidermis. Sequence analysis showed that the 210-kD protein is homologous to the keratin- binding proteins desmoplakin, bullous pemphigoid antigen 1, and plectin. These data suggest that the 210-kD protein may link the cornified envelope to desmosomes and keratin filaments. We propose that the 210-kD protein be named "envoplakin."     

In vitro analysis of mesenchymal influences on the differentiation of stomach epithelial cells of the chicken embryo

It is well established that epithelial-mesenchymal interactions play important roles in the differentiation of stomach epithelial cells in the chicken embryo. To analyze mesenchymal influences on the differentiation of the epithelial cells, we developed a tissue culture system for stomach (proventriculus and gizzard) epithelia of chicken embryo, and examined their differentiation in the presence or absence of mesenchyme. Stomach epithelium from 6-day chicken embryo did not express embryonic chicken pepsinogen (ECPg), a marker molecule of glandular epithelial cells of proventriculus, while it expressed marker molecules of epithelial cells of the luminal surface of stomach, when cultured alone on the Millipore filter, covered with the gel consisting of extracellular matrix components. When the epithelium was recombined with mesenchyme separated by the filter, differentiation of the epithelium was affected by the recombined mesenchyme. Proventricular and lung mesenchymes induced the expression of ECPg in epithelial cells, and the expression was extensive when the gel contained basement membrane components. Proventricular and gizzard epithelia showed different responses to the mesenchymal action. We tested the effects of some growth factors on the differentiation of epithelial cells using this culture system. Furthermore we devised a "conditioned semi-solid medium experiment" for analysis of the inductive properties of proventricular and lung mesenchymes. The results of this experiment clearly demonstrated for the first time that diffusible factors from mesenchyme induce the differentiation of glandular epithelial cells in the absence of mesenchymal cells.     

Expression of tenascin in bile duct cancer of hamster liver by combined treatment of dimethylnitrosamine with Opisthorchis viverrini infections

Tenascin is an extracellular matrix glycoprotein known to be an essential factor for the modulation of reciprocal interactions between the epithelium and mesenchyme during embryogenesis and tumourigenesis. The interactions between the expression of tenascin in the liver of Syrian golden hamster and the development of bile duct cancer in an Opisthorchis viverrini-associated cholangiocarcinoma model were investigated. The tenascin was expressed in connective tissues surrounding the dilated ducts, ductal rims and the stroma of cancers, and strongly in the stroma flame of necrotic cancer nodules. The mRNA signal for tenascin was also recognized in the stroma cells. The potential roles of tenascin as prognostic tumour markers are discussed.     

Syndecan and tenascin expression is induced by epithelial-mesenchymal interactions in embryonic tooth mesenchyme

Morphogenesis of embryonic organs is regulated by epithelial-mesenchymal interactions associating with changes in the extracellular matrix (ECM). The response of the cells to the changes in the ECM must involve integral cell surface molecules that recognize their matrix ligand and initiate transmission of signal intracellularly. We have studied the expression of the cell surface proteoglycan, syndecan, which is a matrix receptor for epithelial cells (Saunders, S., M. Jalkanen, S. O'Farrell, and M. Bernfield. J. Cell Biol. In press.), and the matrix glycoprotein, tenascin, which has been proposed to be involved in epithelial-mesenchymal interactions (Chiquet-Ehrismann, R., E. J. Mackie, C. A. Pearson, and T. Sakakura. 1986. Cell. 47:131-139) in experimental tissue recombinations of dental epithelium and mesenchyme. Our earlier studies have shown that in mouse embryos both syndecan and tenascin are intensely expressed in the condensing dental mesenchyme surrounding the epithelial bud (Thesleff, I., M. Jalkanen, S. Vainio, and M. Bernfield. 1988. Dev. Biol. 129:565-572; Thesleff, I., E. Mackie, S. Vainio, and R. Chiquet-Ehrismann. 1987. Development. 101:289-296). Analysis of rat-mouse tissue recombinants by a monoclonal antibody against the murine syndecan showed that the presumptive dental epithelium induces the expression of syndecan in the underlying mesenchyme. The expression of tenascin was induced in the dental mesenchyme in the same area as syndecan. The syndecan and tenascin positive areas increased with time of epithelial-mesenchymal contact. Other ECM molecules, laminin, type III collagen, and fibronectin, did not show a staining pattern similar to that of syndecan and tenascin. Oral epithelium from older embryos had lost its ability to induce syndecan expression but the presumptive dental epithelium induced syndecan expression even in oral mesenchyme of older embryos. Our results indicate that the expression of syndecan and tenascin in the tooth mesenchyme is regulated by epithelial-mesenchymal interactions. Because of their early appearance, syndecan and tenascin may be used to study the molecular regulation of this interaction. The similar distribution patterns of syndecan and tenascin in vivo and in vitro and their early appearance as a result of epithelial-mesenchymal interaction suggest that these molecules may be involved in the condensation and differentiation of dental mesenchymal cells.     

Tenascin is associated with chondrogenic and osteogenic differentiation in vivo and promotes chondrogenesis in vitro

The tissue distribution of the extracellular matrix glycoprotein, tenascin, during cartilage and bone development in rodents has been investigated by immunohistochemistry. Tenascin was present in condensing mesenchyme of cartilage anlagen, but not in the surrounding mesenchyme. In fully differentiated cartilages, tenascin was only present in the perichondrium. In bones that form by endochondral ossification, tenascin reappeared around the osteogenic cells invading the cartilage model. Tenascin was also present in the condensing mesenchyme of developing bones that form by intramembranous ossification and later was present around the spicules of forming bone. Tenascin was absent from mature bone matrix but persisted on periosteal and endosteal surfaces. Immunofluorescent staining of wing bud cultures from chick embryos showed large amounts of tenascin in the forming cartilage nodules. Cultures grown on a substrate of tenascin produced more cartilage nodules than cultures grown on tissue culture plastic. Tenascin in the culture medium inhibited the attachment of wing bud cells to fibronectin-coated substrates. We propose that tenascin plays an important role in chondrogenesis by modulating fibronectin-cell interactions and causing cell rounding and condensation.     

Mesenchymal control of branching pattern in the fetal mouse lung

The effect of mesenchyme on specialization of respiratory epithelium in the fetal mouse was tested in organ cultures. Heterologous combinations were made between respiratory and non-respiratory lung epithelia and the corresponding mesenchymes. Isolated terminal respiratory buds of fetal mouse lungs were recombined with mesenchyme from chick lung parabronchi, mouse trachea or from the avascular, non-respiratory air sacs of chick lungs. Isolated non-branching chick air sacs were combined with mouse terminal bud mesenchyme or mesenchyme from the respiratory branches of chick lungs. Air sac epithelia branched in a pattern characteristic of the chick lung when combined with chick respiratory mesenchyme and in a pattern characteristic of mouse lung when combined with mouse terminal bud mesenchyme. Mouse terminal bud epithelia did not branch with either mouse tracheal mesenchyme or chick air sac mesenchyme but branched in a chick pattern with chick parabronchial mesenchyme. Electron microscopic examination of the cultures showed that all chick air sac epithelial cultures failed to produce surfactant (lamellar bodies) even when they branched. Control cultures of mouse terminal buds contained large numbers of lamellar bodies; mesenchyme which suppressed branching reduced the number of lamellar bodies to only a few in a small proportion of the cells. Culture medium supplemented with growth factors and hormones increased the number of lamellar bodies in heterologous mouse combinations but did not bring the number to control levels. Supplemented medium had no effect on lamellar body production by chick air sac epithelium. The results indicate that branching pattern is determined by the mesenchyme surrounding the epithelial primordium. However, the capacity to synthesize surfactant is determined by the source of the epithelium; mesenchyme may control the degree of expression but not the absolute presence or absence of the differentiated condition.     

Differentiation of proventricular epithelium in xenoplastic associations with mesenchymal or fibroblastic cells

Summary Proventricular epithelium (PV epithelium) from 6-day chicken embryos was associated with cultured cells, derived from fetal rat small intestine, or with fetal rat or human skin fibroblasts. The cytodifferentiation of PV epithelium was investigated using antibodies to chicken pepsinogen, a marker protein of PV epithelium, and to chicken sucrase, a marker enzyme of the small-intestinal brush-border membrane. PV epithelium formed complex glands and produced pepsinogen in association with cultured gut mesenchymal cells and skin fibroblasts. Its development was comparable to that achieved under the influence of PV mesenchyme. PV epithelial development was severely inhibited, however, under the influence of intact chicken or rat intestinal mesenchyme. The data are consistent with the idea that during the first step of epithelial-mesenchymal interactions, the epithelium and not the mesenchyme may be responsible for the determination of the developmental fate.     

Changes in the distribution of tenascin and fibronectin in the mouse ovary during folliculogenesis, atresia, corpus luteum formation and luteolysis

Tenascin and fibronectin are components of the extracellular matrices that oppose and promote adhesion, respectively. Using immunohistochemical techniques, we studied the distribution of tenascin and fibronectin in the mouse ovary, in which dynamic reconstruction and degeneration occur during folliculogenesis, atresia, ovulation, corpus luteum formation and luteolysis. In growing follicles, tenascin was only detected in the theca externa layer, while fibronectin was detected in the theca externa layer, theca interna layer and basement membrane. During follicular atresia, granulosa cells, which are surrounded by the basement membrane, began to die through apoptosis. In atretic follicles, tenascin was detected in the basement membrane and theca externa layer. Distribution of fibronectin in atretic follicles was similar to that in healthy growing follicles, except that granulosa cells were slightly immunopositive for fibronectin. In young corpus luteum, luteal cells exhibit high 3 beta -hydroxysteroid dehydrogenase (3 beta -HSD) activity, an enzyme indispensable for progesterone production. Tenascin was barely detected in young luteal cells. 3 beta -HSD activity in luteal cells declines with corpus luteum age, and in older corpus luteum there is an increase in apoptotic death of luteal cells. Tenascin was intensely immunopositive in old luteal cells.In contrast, fibronectin immunostaining in luteal cells was relatively constant during corpus luteum formation and luteolysis. Our observations suggest that tenascin is critical in controlling the degenerative changes of tissues in mouse ovaries. Moreover, in all circumstances observed in this study, tenascin always co-localized with fibronectin, suggesting fibronectin is indispensable for the function of tenascin.     

Localization of putative stem cells in dental epithelium and their association with Notch and FGF signaling.

The continuously growing mouse incisor is an excellent model to analyze the mechanisms for stem cell lineage. We designed an organ culture method for the apical end of the incisor and analyzed the epithelial cell lineage by 5-bromo-2'-deoxyuridine and DiI labeling. Our results indicate that stem cells reside in the cervical loop epithelium consisting of a central core of stellate reticulum cells surrounded by a layer of basal epithelial cells, and that they give rise to transit-amplifying progeny differentiating into enamel forming ameloblasts. We identified slowly dividing cells among the Notch1-expressing stellate reticulum cells in specific locations near the basal epithelial cells expressing lunatic fringe, a secretory molecule modulating Notch signaling. It is known from tissue recombination studies that in the mouse incisor the mesenchyme regulates the continuous growth of epithelium. Expression of Fgf-3 and Fgf-10 were restricted to the mesenchyme underlying the basal epithelial cells and the transit-amplifying cells expressing their receptors Fgfr1b and Fgfr2b. When FGF-10 protein was applied with beads on the cultured cervical loop epithelium it stimulated cell proliferation as well as expression of lunatic fringe. We present a model in which FGF signaling from the mesenchyme regulates the Notch pathway in dental epithelial stem cells via stimulation of lunatic fringe expression and, thereby, has a central role in coupling the mitogenesis and fate decision of stem cells.     

Neutral morphogenetic activity of epithelium in heterologous tissue recombinations

To assess the existence of specific and nonspecific epithelial instructions for mesenchymal cell differentiation we compared homospecific and heterospecific mouse and quail tissue recombinations. In heterospecific recombinants between trypsin-dissociated mouse molar mesenchyme and quail epithelia neither odontoblasts nor chondrocytes differentiated. Cartilage appeared if the quail epithelium was contaminated with homologous limb mesenchyme and odontoblasts differentiated if the mouse dental epithelium was contaminated with dental papilla cells.     

Altered tenascin expression during spontaneous endometrial carcinogenesis in the bdii/han rat

The BDII/Han rat develops spontaneous endometrial adenocarcinoma, which appears virtually identical histologically to human endometrial adenocarcinoma. The incidence rate of cancer formation in the rat is 90% and the mean lifetime of the animals is 22 months. This animal model therefore, is useful in the study of molecular aspects of spontaneous transformation as well as mammalian neoplastic progression. In this study we address the in-situ expression of tenascin, an extracellular matrix glycoprotein, during normal cyclic growth, during development of proliferative states, and during malignant transformation of the endometrium. Trace amounts of immunocytochemically detectable tenascin were found in 10% of young BDII/Han rats with a normal estrus cycle. In these inbred animals no tenascin was detectable in uteri without neoplastic progressive alterations of the endometrium. Tenascin immunoreactivity first appeared during proliferation in one of three uteri with cystic glandular hyperplasia. Prominent tenascin expression was detectable in all adenomatous hyperplasia, but restricted to the stromal mesenchyme, that surrounded the glands. In all endometrial adenocarcinomas tested, essentially the entire extracellular space of the stromal mesenchyme was immunoreactive with anti-tenascin antibodies while the epithelial glands themselves were negative. This staining pattern was observed independent of the degree of tumor differentiation or extent of myometrial invasion. The tenascin staining pattern was not significantly altered in tumors transplanted into the soft tissues of the neck of female BDII/Han rats. From our studies we conclude that tenascin may be a marker for the early detection of proliferative endometrial states. Further, previous investigation by us showing nearly identical findings in human endometrium reinforces the value of this animal model system in the study of human epithelial hyperplastic conditions including those associated with malignancies of the endometrium.