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I Thesleff

Publications and source records attributed to I Thesleff.

At least 73 records · Page 4Linked to original sources
PubMed1992

Expression of type I collagen pro-alpha 2 chain mRNA in adult human permanent teeth as revealed by in situ hybridization.

The expression of the gene COL1A2, coding for the pro-alpha 2 chain of type I pro-collagen, was analyzed in fully developed human permanent teeth. The teeth were fixed with formalin, demineralized with EDTA for about ten weeks, and embedded in paraffin. Pro-alpha 2(I) mRNA was localized in the sections by in situ hybridization, with use of [35S)]-labeled single-stranded RNA probes. The amount of mRNA for pro-alpha 2(I) collagen chain, as indicated by the relative densities of silver grains and the grain counts per cell in autoradiography, was high in odontoblasts, whereas in pulpal fibroblasts it was low. High levels of pro-alpha 2(I)mRNA expression were also present in those odontoblasts which had elaborated new dentin matrix in response to dental caries. Expression in the periodontal ligament, including the cementoblast layer, was slightly stronger than that in odontoblasts. The intense expression of pro-alpha 2(I) mRNA in odontoblasts of adult teeth suggests that even after the completion of primary dentin formation, they continue to synthesize heterotrimeric type I collagen molecules. Cell type-specific differences in the expression of pro-alpha 2(I) mRNA imply that type I collagen probably plays a major role in the regulation of the structure and function of dental tissues. Finally, in situ hybridization enabled pro-alpha 2(I) collagen mRNA to be detected in tissue sections even after prolonged demineralization, and thus it proved to be a valuable technique for analysis of gene expression in adult dental tissues, as shown here for COL1A2.

Adult↗
PubMed1992

The role of growth factors in determination and differentiation of the odontoblastic cell lineage.

In developing teeth the differentiation of odontoblasts is triggered by the enamel epithelium and is tightly coupled with morphogenesis. There is substantial evidence that even in mature teeth the cells of the dental pulp retain the capability to differentiate into odontoblasts under suitable conditions. However, cells from other than the dental mesenchymal cell lineage apparently do not possess this potential. Thus, it is conceivable that the dental mesenchymal cells acquire cell type-specific potential to differentiate into odontoblasts during their developmental history. Therefore, the understanding of the mechanisms which regulate the terminal differentiation of odontoblasts requires that the molecular changes and mechanisms that are associated with their progressive determination be clarified. It can be speculated that there are key transition points in the developmental sequence during which the mesenchymal cells acquire new levels of differentiation. These include, (1) the condensation of the neural crest-derived mesenchymal cells around the epithelial bud, (2) their entrance into the dental papilla lineage during cap stage, and (3) the differentiation of the cells underlying the enamel epithelium into odontoblasts during bell stage. The transition points are conceivably characterized by amplification or onset of expression of new sets of genes encoding transcription factors, growth factors as well as structural proteins. We have applied in situ hybridization for localization of the expression of two growth factors during mouse molar morphogenesis: transforming growth factor beta 1 (TGF beta 1) and int-2 (a proto-oncogene coding for a fibroblast growth factor-related protein). During bud stage, expression of TGF beta 1 was first detected in the epithelium and shortly thereafter in the condensed dental mesenchyme. The expression was weak during early bell stage but a high number of transcripts appeared in secretory odontoblasts as well as in presecretory ameloblasts. int-2 mRNA appeared in the dental papilla mesenchyme at the onset of cap stage, persisted in the cuspal mesenchyme during bell stage and was lost upon completion of morphogenesis. Our findings suggest that cell type-specific expression of TGF beta 1 and int-2 is associated with phenotypic properties of the odontoblastic cell lineage. For instance, TGF beta 1 may regulate matrix deposition by increasing tenascin and syndecan expression in the condensed dental mesenchyme and by controlling dentin matrix deposition by odontoblasts. TGF beta 1 and int-2 may also be involved in signalling between the epithelial and mesenchymal tissues and in regulation of gene expression at the transition points of the developmental sequence that leads to the differentiation of odontoblasts.

Animals↗
PubMed1991

Dependence of kidney morphogenesis on the expression of nerve growth factor receptor.

Nerve growth factor receptor (NGFR) serves as the binding site for the neurotrophic growth factors. Although NGFR has been found in several embryonic tissues outside the nervous system, the function of NGFR in embryogenesis of non-neuronal organs remains unknown. NGFR is transiently synthesized by embryonic rat kidney and disappears from nephrons upon their terminal differentiation. Anti-sense oligonucleotide inhibition of NGFR expression inhibits kidney morphogenesis. Therefore, NGFR is required not only for development of the nervous system, but also for differentiation of the kidney tubules.

Animals↗
PubMed1991

Syndecan from embryonic tooth mesenchyme binds tenascin.

Syndecan is a cell surface heparan sulfate-rich proteoglycan found on various epithelial cells but also in some embryonic mesenchymal tissues. We have immunoisolated syndecan from embryonic tooth mesenchyme that appeared as a 250-300-kDa molecule (Kav = 0.3 in Sepharose 4B), containing only heparan sulfate side chains (Mr = 35,000). Northern analysis of whole tooth germs and tooth mesenchymes also revealed high expression of syndecan mRNAs (2.6 and 3.4 kilobases). In the binding assay utilizing nitrocellulose as a solid phase to immobilize matrix molecules, syndecan immunoisolated from tooth mesenchyme revealed binding to tenascin, and this interaction was shown to be mediated via heparan sulfate side chains. In contrast, syndecan from mouse mammary epithelial cells showed only weak interaction with tenascin. We propose that syndecan and tenascin may represent interactions of a cell surface receptor and a matrix ligand involved in mesenchymal cell condensation and differentiation during early organogenesis.

Animals↗
PubMed1991

Expression of syndecan gene is induced early, is transient, and correlates with changes in mesenchymal cell proliferation during tooth organogenesis.

Syndecan is an integral cell surface proteoglycan which contains an extracellular matrix-binding domain and a cytoskeleton-associated domain and may therefore transfer changes in the extracellular environment to cellular behavior. Changes in syndecan gene expression during embryonic and early postnatal mouse tooth development were analyzed by in situ hybridization and compared with the distribution of syndecan core protein and cell proliferation studied by immunohistochemistry. Syndecan RNA became accumulated in the condensing mesenchymal cells around the invaginating epithelial tooth bud during early development, and this accumulation became more intense when morphogenesis advanced to the cap stage. During the bell stage, when the cuspal pattern of the tooth is established, syndecan transcripts were lost, and RNA was not detected in the terminally differentiated or postmitotic odontoblasts. In the epithelium, syndecan RNA was intensely expressed in the invaginating epithelial bud, but the expression was reduced during the cap and bell stages. However, local stimulation in syndecan gene expression was observed in the epithelial preameloblasts immediately preceding their terminal differentiation into ameloblasts, which was accompanied by a complete loss of transcripts. There was a close correlation between the changes in syndecan transcripts and the distribution of syndecan core protein. Furthermore, analysis of cell proliferation by immunohistochemical detection of BrdU incorporation revealed that in the mesenchyme, but not in the epithelium, syndecan was intensely expressed by proliferating cells. The analysis of mRNA by Northern blot indicated that the transcripts in mesenchymal and epithelial cells were of similar size. In the slot-blot analysis the changes in syndecan transcripts correlated with the overall changes observed in the in situ hybridization analysis. The role of tissue interactions in the regulation of the syndecan gene was studied by using tissue recombination cultures of separated epithelial and mesenchymal components of the early tooth germ. The in situ hybridization and Northern blot analysis of these explants showed that the expression was increased in the mesenchyme cultured in contact with the epithelium. Our results indicate that syndecan gene expression in the embryonic tooth mesenchyme is induced by epithelial-mesenchymal interactions and thereafter expressed stage-dependently and transiently by the differentiating cells during organogenesis. The association of syndecan expression with mesenchymal cell proliferation raises the possibility that, in addition to behaving as a matrix receptor, syndecan may have a role in controlling growth and that syndecan may have different functions in epithelial and mesenchymal cells.

Animals↗
PubMed1991

Induced expression of syndecan in healing wounds.

We have studied the expression of an integral cell surface proteoglycan, syndecan, during the healing of cutaneous wounds, using immunohistochemical and in situ hybridization methods. In normal mouse skin, both syndecan antigen and mRNA were found to be expressed exclusively by epidermal and hair follicle cells. After incision and subsequent suturing, remarkably increased amounts of syndecan on the cell surfaces of migrating and proliferating epidermal cells and on hair follicle cells adjacent to wound margins were noted. This increased syndecan expression was shown to be a consequence of greater amounts of syndecan mRNA. Induction was observed already 1 d after wounding, was most significant at the time of intense cell proliferation, and was still observable 14 d after incision. The migrating cells of the leading edge of the epithelium also showed enhanced syndecan expression, although clearly less than that seen in the proliferating epithelium. The merging epithelial cells at the site of incision showed little or no syndecan expression; increased syndecan expression, however, was detected during later epithelial stratification. When wounds were left unsutured, in situ hybridization experiments also revealed scattered syndecan-positive signals in the granulation tissue near the migrating epidermal sheet. By immunohistochemical analysis, positive staining in granulation tissue was observed around vascular endothelial cells in a subpopulation of growing capillaries. Induction of syndecan in granulation tissue both at the protein and mRNA levels was temporally and spatially highly restricted. Granulation tissue, which formed in viscose cellulose sponge cylinders placed under the skin of rats, was also found to produce 3.4 and 2.6 kb mRNA species of syndecan similar to that observed in the normal murine mammary epithelial cell line, NMuMG. These results suggest that syndecan may have a unique and important role as a cell adhesion and a growth factor-binding molecule not only during embryogenesis but also during tissue regeneration in mature tissues.

Animals↗
PubMed1991

Immunohistochemical localization of epidermal growth factor receptors in human gingival epithelia.

Epidermal growth factor (EGF) is a small molecular weight polypeptide which is thought to have important functions in epithelial growth and differentiation and in wound healing. EGF exerts its action on cells through binding to a cell surface receptor. Using immunohistochemistry and a monoclonal antibody (mAb) directed against the EGF receptor, we have examined gingival specimens of periodontally healthy individuals and patients with adult adult (AP) and juvenile periodontitis (JP), as well as epithelial cell rests of Malassez. EGF receptors were expressed at high levels on the cell surface of basal cell layers of gingival epithelium. In normal junctional epithelium, on the other hand, specific labeling was faint or negative, indicating that receptors are poorly expressed or absent in these cells. No differences were detected between uninflamed gingival specimens of periodontally healthy subjects and of patients with JP. Instead, in biopsies of inflamed tissue from AP patients, an intense cell surface labeling was revealed in proliferating epithelial cells. Moreover, the epithelial cell rests of Malassez bound the antibody intensely. The results suggest that EGF is involved in control of epithelial growth and differentiation in periodontal tissues.

Adolescent↗
PubMed1991

Immunohistochemical localization of the matrix glycoproteins--tenascin and the ED-sequence-containing form of cellular fibronectin--in human permanent teeth and periodontal ligament.

The expression of two matrix glycoproteins, tenascin and cellular fibronectin (cFN), has been studied in fully developed human permanent teeth, periodontal ligament, and alveolar bone, in both frozen and paraffin-processed material. Polyclonal antibodies to tenascin and a monoclonal antibody recognizing the ED sequence specific to at least some forms of cFN were used. Staining for both tenascin and cFN was positive in the dental pulp, odontoblastic layer, cementoblast-pre-cementum zone, and on the periosteal as well as endosteal surfaces of the alveolar bone. In the periodontal ligament, cFN was evenly distributed, whereas tenascin was accumulated in the attachment zones. Pre-dentin stained for tenascin but not for cFN. Mineralized dentin and cementum were tenascin- and cFN-negative. The relative staining intensity for tenascin was greater than that for cFN in the cementoblast-pre-cementum layer and in the attachment zones of the periodontal ligament, whereas cFN stained more intensely in the pulp. In frozen material, antigenicities were well-preserved. Paraffin processing facilitated precise recognition of tissue morphology, but the antigenicity of cFN was lost. The co-expression of tenascin and cFN in the dental pulp, cementogenic zone, and on the surfaces of the alveolar bone may reflect the ability of the cells to deposit mineralized tissue matrices. The pronounced expression of tenascin in the interfaces between mineralized and non-mineralized tissues suggests that it is functionally associated with mechanical stress and may thus have at least two distinct functions. The relative amounts of the two matrix glycoproteins may contribute to regulation of tissue structure.

Adult↗
PubMed1991

Associations between transforming growth factor beta 1 RNA expression and epithelial-mesenchymal interactions during tooth morphogenesis.

We have studied the expression of transforming growth factor beta-1 (TGF-beta 1) RNA during mouse tooth development, using in situ hybridization and experimental tissue recombinations. Analysis of the serial sections revealed the appearance of local expression of TGF-beta 1 RNA in the dental epithelium at bud-staged teeth (13-day embryos). Just before transition to the cap stage, TGF-beta 1 RNA expression rapidly increased in the epithelial bud, and it also extended to the condensed dental mesenchyme. At cap stage (14- and 15-day embryos), there was an intense expression of TGF-beta 1 RNA in the morphologically active cervical loops of the dental epithelium. During early bell stage (16- and 17-day embryos), TGF-beta 1 RNA expression was detected in the inner enamel epithelium where it subsequently almost disappeared (18-day embryos). After birth TGF-beta 1 transcripts transiently appeared in these cells when they were differentiating into ameloblasts (1-day mice). The transcripts were lost from the ameloblasts when they became secretory (4-day mice), but the expression continued in ameloblasts in enamel-free areas. Transient expression of TGF-beta 1 RNA was also detected in epithelial stratum intermedium cells at the time of ameloblast differentiation. In the mesenchyme, TGF-beta 1 RNA was not detected during bell stage until it appeared in differentiated odontoblasts (18-day embryos). The secretory odontoblasts continued to express TGF-beta 1 RNA at all stages studied including the odontoblasts of incisor roots. Analysis of the distribution of bromodeoxyuridine (BrdU) incorporation indicated apparent correlations between TGF-beta 1 RNA expression and cell proliferation at the bud and cap stages but not at later stages of tooth development. Tissue recombination experiments of bud-staged (13-day embryos) dental and non-dental tissues showed that tooth epithelium, when cultured together with tooth mesenchyme, expressed TGF-beta 1 RNA. When the tooth epithelium was combined with non-dental jaw mesenchyme, TGF-beta 1 transcripts were not expressed. However, TGF-beta 1 RNA expression was seen in oral epithelium cultured with dental mesenchyme, while no expression of TGF-beta 1 transcripts was seen in the oral epithelium during normal development. Thus, TGF-beta 1 RNA expression seems to be regulated by epithelial-mesenchymal interactions.

Animals↗
PubMed1991

Tooth development.

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Growth Substances↗
PubMed1991

Advances in histological methods open up new perspectives for craniofacial growth research.

Changes in the tissue architecture and composition which accompany growth and development have traditionally been mapped using histological methods. The modern technology now offers new possibilities which can be used in connection with light microscopy and electron microscopy. These techniques, particularly immunohistochemistry and in situ hybridization allow studies on spatial and temporal changes in molecular patterns of substances during tissue organization and cell differentiation. In this paper, we describe the principles of immunohistology, autoradiography, and in situ hybridization, and review our recent studies in which we have applied such methods to assess craniofacial development. We have used autoradiography to localize cell proliferation and epidermal growth factor (EGF) receptors in the developing mandibular condyle. We have also used immunohistochemistry to localize the extracellular matrix component, tenascin, in differentiating chondrocytes of the mandibular condyle, employing specific antibodies. In studies on the odontogenic potential of dental papilla mesenchyme, we have used hybridoma technology, and produced monoclonal antibodies against dental papilla mesenchyme. Most recently, we have used in situ hybridization, which allows detection of gene expression in tissue sections to localize transcripts of a fibroblast-growth-factor related gene (Int-2 proto-oncogene) in developing teeth. In future, successful combination of such new histological methods and traditional experimental procedures can be expected to produce new answers to the questions about the regulation of craniofacial growth.

Facial Bones↗
PubMed1990

Comparison of the distribution patterns of tenascin and alkaline phosphatase in developing teeth, cartilage, and bone of rats and mice.

Tenascin is a glycoprotein of the extracellular matrix, which has been associated with differentiation of hard tissue forming cells. Alkaline phosphatase (AP) is involved in calcification, and it has also been suggested to function in cell differentiation. We have compared the distributions of tenascin and AP in the developing skull and teeth of embryonic and growing rats and mice. Tenascin was localized by immuno-Peroxidase and AP by enzyme histochemical staining of tissue sections. Both tenascin and AP were largely restricted to bone, cartilage, and teeth. In cartilage, tenascin was expressed in the perichondrium, whereas AP activity was detected only in the hypertrophic cartilage. In growing intramembranous bone, tenascin and AP were expressed in the periosteum and endosteum. AP activity was restricted to the inner layer of the periosteum, whereas tenascin expression extended to the more superficial layers. In bud-staged teeth tenascin but no AP activity was localized in the condensing mesenchymal cells around the epithelial bud. At the bell stage both tenascin and AP activity were localized in the cuspal mesenchyme, and the intensity of staining decreased towards the cervical region. In summary, tenascin was present at all sites of AP activity except in the epithelial cells of the enamel organ and the hypertrophic cartilage of the mandibular condyle. In mesenchymal tissues tenascin was more widely distributed than AP. It can be suggested that tenascin has functions at earlier stages of hard tissue formation than AP.

Alkaline Phosphatase↗
PubMed1990

Molecular changes during determination and differentiation of the dental mesenchymal cell lineage.

The lineage of dental mesenchymal cells originates in the cranial neural crest, and after sequential determination and differentiation, gives rise to all structures of the tooth and its supporting tissues, except the enamel. Reciprocal interactions between the epithelial and mesenchymal tissues are conceivably the most important regulators of dental mesenchymal cell differentiation. The molecular mechanisms of this epigenetic regulation are not known at present. In order to examine the mechanisms of regulation of gene expression in the lineage of dental mesenchymal cells, information is needed on the molecular changes that accompany advancing differentiation. By using the molar tooth germ of mouse embryos as a model system, the changes in the expression of some molecules have been analysed by immunohistological localization and in situ hybridization, and the roles of tissue interactions in this process examined. This has shown that syndecan, a recently characterized cell surface proteoglycan, and tenascin, a matrix glycoprotein, appear in the condensing dental mesenchyme during the bud stage of tooth development. During the cap stage, dental mesenchyme is characterized by continued intense expression of syndecan, but this is lost during terminal differentiation of odontoblasts. Tenascin and syndecan may mediate cell-matrix interactions during condensation of dental mesenchymal cells. Expression of the Int-2 proto-oncogene, coding for a fibroblast growth factor-related molecule, can be detected by in situ hybridization in dental mesenchyme at the cap stage. This expression persists in cuspal mesenchyme at the bell stage but is lost from odontoblasts and from pulpal mesenchyme at progressive stages of tooth development. The advancement of tooth morphogenesis from cap to bell stage is accompanied by expression of alkaline phosphatase in the cuspal mesenchyme. Also tenascin, which is only weakly expressed during the cap stage, appears in the cuspal areas and shows codistribution with alkaline phosphatase. These observations indicate that the sequential determination and differentiation of the dental mesenchymal cells are characterized by a cascade of specific molecular changes. The cell surface proteoglycan syndecan and the Int-2 proto-oncogene are specific and transient markers of early dental mesenchymal cell differentiation. This information allows studies on the mechanisms of developmental regulation. These experimental tissue recombination studies indicate that the expression of syndecan and tenascin in the early dental mesenchyme is induced by the presumptive dental epithelium.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1989

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.

Animals↗
PubMed1989

Growth factors and tooth development.

The effects of various growth factors on tooth development were studied in organ cultures of mouse embryonic tooth germs. Transferrin was shown to be a necessary growth factor for early tooth morphogenesis. Transferrin was required for the development of bud- and early cap-staged teeth, and it was shown to be the only serum protein that was needed by early cap-staged teeth in organ culture. Promotion of tooth morphogenesis and dental cell differentiation was shown to be based on the stimulation of cell proliferation. The roles of polypeptide growth factors in tooth development were studied by adding these factors to the transferrin-containing chemically-defined culture medium which supports early tooth morphogenesis and cell differentiation. Fibroblast growth factor or platelet-derived growth factor did not affect cell proliferation or morphogenesis of tooth germs in culture. On the contrary, epidermal growth factor (EGF) stimulated cell proliferation in tooth explants, but at the same time inhibited tooth morphogenesis and dental cell differentiation. Autoradiographic localization of proliferating cells revealed that dental tissues responded to EGF with different proliferation rates. The responsiveness to EGF was stage-dependent, early cap-staged teeth were sensitive to EGF but late cap-staged and bell-staged teeth developed normally in the presence of EGF in the culture medium. The presence and distribution of receptors for both transferrin and EGF were studied in mouse embryonic teeth at various developmental stages by incubating freshly-separated tooth germs with 125Iodine-labeled transferrin or EGF, and then processing the tissues for autoradiography.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗