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H Lesot

Publications and source records attributed to H Lesot.

At least 19 recordsLinked to original sources
PubMed2000

Designing new treatment strategies in vital pulp therapy.

OBJECTIVES: The development of strategies in vital pulp therapy, which aim to maintain vitality and function of the dentine-pulp complex, represents a major focus of attention. Recent progress in understanding the molecular and cellular changes during tooth development and how they are mimicked during dental tissue repair offers the opportunity to now assess whether this knowledge can be exploited to design new treatment strategies in vital pulp therapy. DATA SOURCES AND STUDY SELECTION: Current literature on the molecular and cellular basis of tooth development and dental tissue repair has been reviewed in the context of stimulating dentinogenic responses in the tooth together with pertinent published abstracts of relevant conferences and personal communications. Tissue events of direct relevance to clinical application for vital pulp therapy are discussed. CONCLUSIONS: The involvement of growth factors and extracellular matrix molecules in signalling and regulating dentinogenic events during tooth development has been identified. During dental tissue repair, many of the processes are mimicked leading to responses of focal deposition of tertiary dentine at injury sites. The nature and specificity of these responses are determined in part by the extent of tissue injury. Traditional clinical strategies are capable of exploiting endogenous signalling molecules in the tissues to develop more effective treatment modalities. Application of exogenous signalling molecules offers opportunities for development of new therapies, although a number of delivery considerations must be addressed before these can be introduced into clinical practice.

Cell Differentiation↗
PubMed2000

The presence of rudimentary odontogenic structures in the mouse embryonic mandible requires reinterpretation of developmental control of first lower molar histomorphogenesis.

In the mouse embryonic maxilla, rudimentary tooth primordia have been identified, which can be mistaken for the first upper molar. In order to determine whether such a situation might exist in the lower jaw as well, tooth development was investigated in the mouse mandibular cheek region during ED 12.5-15.0. A combination of histology, morphometry and computer-aided 3D reconstructions demonstrated the existence of rudimentary dental structures, whose gradual appearance and regression was associated with the segmental progress of odontogenesis along the mesio-distal axis of the jaw: 1) At ED 12.5, the mesial segment (MS) was the most prominent part of the dental epithelial invagination. It included an asymmetrically budding dental lamina. The MS, although generally mistaken for the lower first molar (M1, primordium, regressed and did not finally participate in M1 cap formation. 2) At ED 13.5, a wide dental bud (called segment R2) appeared distally to the MS. Although the R2 segment transiently represented the predominant part of the dental epithelium at ED13.5, it participated only in the formation of the mesial end of the M1 cap. 3) The top of the R2 segment at ED13.5 was not the precursor of the enamel knot (EK), contrary to what has been assumed. 4) The central segment of the M1 cap as well as the EK developed later and distally to the R2 segment. 5) Time-space specific apoptosis correlated with the retardation in growth of the R2 segment as well as with strong regressive changes in the epithelium situated mesially to it. These highlight the need to reinterpret current molecular data on early M1 development in the mouse in order to correlate the expression of signalling molecules with specific morphogenetic events in the appropriate antemolar or molar segments of the embryonic mandible.

Animals↗
PubMed2000

Regeneration of halved embryonic lower first mouse molars: correlation with the distribution pattern of non dividing IDE cells, the putative organizers of morphogenetic units, the cusps.

Recently we demonstrated that non-cycling, cap-stage, mouse molar inner dental epithelial (IDE) cells corresponding to the primary enamel knot (EK) area underwent a coordinated temporo-spatial patterning leading to their patchy irregular segregation at the tips of the forming cusps. These non-cycling cells were suggested to perhaps represent the organizers of the morphogenetic units (OMU), the cusps. The present study has analyzed the regenerative capacity of halved cap-stage first lower mouse molars through three dimensional (3D) reconstructions. Partial regeneration of the anterior half and possible complete regeneration of the posterior half were documented. Using BrdU (5-bromo-2'-deoxyuridine) labeling and 3D reconstructions of the IDE, we have correlated the patterns of cusp regeneration with the distribution of BrdU negative IDE cells. These data support a morphogenetic role for the non-cycling IDE cells.

Animals↗
PubMed2000

Differential expression of laminin-5 subunits during incisor and molar development in the mouse.

Rodent incisors are continuously growing teeth and enamel deposition is restricted to the labial side. In the present study, the expression of laminin-5 subunits (alpha3, beta3 and gamma2) has been analyzed by in situ hybridization in developing mouse lower incisors and compared to that reported in the molar. At the bud stage (E12), mRNAs for all subunits were detected in the whole epithelial thickening. At E14, when histogenesis had started, transcripts for alpha3 and gamma2 subunits were restricted to the outer dental epithelium (ODE), whereas the beta3 subunit was intensely expressed in the inner dental epithelium (IDE). A transient expression for alpha3 subunit was seen in the enamel knot area and disappeared at E15. Subsequently, all laminin-5 subunit genes were re-expressed in differentiating ameloblasts on the labial side. Similar patterns of transcription were observed in incisor and molar, suggesting that the differential expression of laminin-5 subunits in the IDE might be involved in the histogenesis of the IDE and ameloblast differentiation. At E16.5, cells of the IDE at the anterior extremity of the incisor and in the anterior part of the lingual IDE expressed transcripts for alpha3 and beta3 but not for gamma2 subunit. Similar expression patterns were observed in the enamel-free areas of the E18 molar. This specific expression might thus be related to cells that do not differentiate as functional ameloblasts. Throughout incisor development, intense expression for all laminin-5 subunits was restricted to the labial side of the cervical loop. The asymmetrical expression of laminin-5 might be related to incisor morphogenesis and to the differences in histogenesis and cytodifferentiation of the IDE that exist in the labial versus lingual aspect of the cervical loop.

Animals↗
PubMed2000

Inhibition of apoptosis in the primary enamel knot does not affect specific tooth crown morphogenesis in the mouse.

The enamel knot (EK), located in the center of cap-stage tooth germs, is a transitory cluster of non-dividing epithelial cells, eventually linked to the outer dental epithelium by the enamel septum (ES). It might act as a signaling center providing positional information for tooth morphogenesis and could regulate the growth of tooth cusps through the induction of secondary signaling EKs. The EK undergoes apoptosis, which could constitute a mechanism whereby the signaling functions of this structure are terminated. Recently, we demonstrated the segregation of 5-bromo-2'-deoxyuridine (BrdU) negative inner dental epithelial (IDE) cells of the EK into as many individual groups of cells as cusps will form and suggested a morphogenetic role for these particular IDE cells. Using Z-VAD-fmk, a specific caspase inhibitor, apoptosis in the primary EK of first mouse lower cap-staged molars and lower incisors cultured in vitro was abrogated. No obvious histological alterations were observed in the incisors, whereas a prominent EK and an ES connecting the outer dental epithelium (ODE) and the BrdU negative IDE cells capping cusp L2 were observed in the molars. EK specific transcription (Shh, Msx-2, Bmp-2, Bmp-4) was down-regulated in the body of these structures with the exception of the associated IDE cells. In these experimental conditions, segregation of non-dividing transcriptionally active IDE cells occurred and a normal cusp pattern was expressed.

Animals↗
PubMed2000

Effects of hepatocyte growth factor anti-sense oligodeoxynucleotides or met D/D genotype on mouse molar crown morphogenesis.

Hepatocyte growth factor (HGF) is considered to be one of the mediators of epithelio-mesenchymal interactions during early organogenesis and to be also involved in the development of murine molars. In the developing tooth, HGF is expressed in the cells of the dental papillae, and c-Met, its receptor, in the cells of dental epithelia. In order to study the functional role played by HGF in tooth development, we tested the effects of HGF translation arrest by anti-sense phosphorothioate oligodeoxynucleotides on E-14 molars cultured in vitro. We also analyzed the histo-morphogenesis and crown cytodifferentiation of transgenic met E-14 molars cultured in vitro. 3D reconstructions revealed perturbations of the cusp pattern. However, histo-morphogenesis and crown cytodifferentiation were normal at the histological level.

Animals↗
PubMed1999

Initial aspects of mineralization at the dentino-enamel junction in embryonic mouse incisor in vivo and in vitro: a tem comparative study.

The frontier between the enamel organ and the dental papilla, the future dentino-enamel junction, undergoes coordinated modifications. The mineralization of the extracellular matrix starts within the predentine, which is a prerequisite for the formation of the first enamel crystallites in vivo. We investigated the dentino-enamel junction using the embryonic mouse incisor as a model. Our data showed that the notion of the dentino-enamel junction should not be restricted to the thin interface classically described. A temporo-spatial survey from the epithelio-mesenchymal junction to the dentino-enamel junction delineated a clear sequence of events characterized by the early deposition of electron-dense granules, followed by the appearance of patches of stippled material at the dentino-enamel junction. The first tiny enamel crystallites appeared in the vicinity of this material which presented a well-ordered alignment. The comparison of data obtained in vivo on 17-, 18-, 19-d-old embryonic incisors with those obtained in vitro using 15-d-old embryonic incisors cultured for 7 d emphasizes the relevance of this sequence. Helicoidal growing crystals were observed in cultured tooth germs but never in vivo.

Amelogenesis↗
PubMed1999

Initial features of the inner dental epithelium histo-morphogenesis in the first lower molar in mouse.

First lower molar development in the mouse was investigated from the cap to early bell stage using histology, morphometry, TEM and 3D reconstructions. This period was characterized by the histogenesis of the enamel organ (EO), folding of the epithelio-mesenchymal junction and growth of the tooth. The histogenesis of the EO and appearance of the enamel knot (EK) were initiated at the early cap stage (ED14). From ED14 to ED15, the anterior and posterior extension of the EK was very prominent whilst the length of the enamel organ did not substantially change. The EK appeared as a dynamic and transitory histological structure including dying and replacement cells. At ED16, the folding of the IDE, which extended over the anterior two thirds of the molar, was the first sign of cuspidogenesis. It was accompanied by a local remodeling of the basement membrane (BM): IDE cells involved in this folding transitorily lost contact with the BM which formed a loop in the mesenchyme. During this period, the growth of the lower M1 along the antero-posterior axis was restricted to the posterior part of the molar. Histogenesis occurred in the whole EO, whilst initial cuspidogenesis was limited to the anterior part of the tooth. Distinct cell populations were thus involved in different contemporary processes leading to changes in the cell density in the mesenchyme, in the mitotic activity, in cell-shape, and cell-matrix interactions in the IDE, and remodeling of the BM where both epithelium and mesenchyme might participate.

Animals↗
PubMed1999

Mouse odontogenesis in vitro: the cap-stage mesenchyme controls individual molar crown morphogenesis.

Day 14 ICR mouse first lower (M1) and upper molars (M1) as well as heterotopic recombinations of M1 epithelium/M1 mesenchyme and M1 epithelium/M1 mesenchyme were cultured for 6, 8 and 10 days on semi-solid medium. Computer-assisted 3D reconstructions were performed to follow the in vitro development of these explants. In vitro culture of cap-stage molars allowed for the emergence of unequivocal morphological features distinctive for M1 versus M1 including the cusp pattern, cusp inclination and tooth specific chronology for odontoblast and ameloblast terminal differentiations. Both M1 epithelium/M1 mesenchyme and M1 epithelium/M1 mesenchyme recombinations developed according to the known developmental fate of the mesenchyme. Our data demonstrate that the cap-stage dental ecto-mesenchyme not only directs tooth class specific morphogenesis, but also individual molar crown features. Furthermore, the mesenchyme apparently also controls the typical mirror symmetry of right and left handed teeth.

Animals↗
PubMed1999

Aspects of cell proliferation kinetics of the inner dental epithelium during mouse molar and incisor morphogenesis: a reappraisal of the role of the enamel knot area.

First lower E-14 and E-16 mouse molars and E-13 lower incisors were cultured in vitro and either sequentially or continuously labelled with BrdU (5-bromo-2'-deoxyuridine). The behaviour of the non-cycling inner dental epithelial cells emerging from the enamel knot area of the molars was analysed by 3D (three dimensional) reconstructions of serial sections. These cells, as well as slow cycling cells underwent a coordinated temporo-spatial patterning leading to their patchy segregation at the tips of the forming cusps. In incisors (in vitro and in vivo), non-cycling cells were also present in the inner dental epithelium of the enamel knot area. However, these cells were not redistributed during incisor morphogenesis. These non-dividing inner dental epithelium cells of the enamel knot area which are either redistributed or not according to the tooth type specific morphogenesis might represent the organizers of morphogenetic units (OMU), the cusps.

Animals↗
PubMed1999

Alterations in the incisor development in the Tabby mouse.

The X-linked tabby (Ta) syndrome in the mouse is homologous to the hypohidrotic ectodermal dysplasia (HED) in humans. As in humans with HED, Ta mice exhibit hypohidrosis, characteristic defects of hairs and tooth abnormalities. To analyze the effects of Ta mutation on lower incisor development, histology, morphometry and computer-aided 3D reconstructions were combined. We observed that Ta mutation had major consequences for incisor development leading to abnormal tooth size and shape, change in the balance between prospective crown- and root-analog tissues and retarded cytodifferentiations. The decrease in size of Ta incisor was observed at ED13.5 and mainly involved the width of the tooth bud. At ED14.5-15.5, the incisor appeared shorter and narrower in the Ta than in the wild type (WT). Growth alterations affected the diameter to a greater extent than the length of the Ta incisor. From ED14.5, changes in the shape interfered with the medio-lateral asymmetry and alterations in the posterior growth of the cervical loop led to a loss of the labio-lingual asymmetry until ED17.0. Although the enamel organ in Ta incisors was smaller than in the WT, a larger proportion of the dental papilla was covered by preameloblasts-ameloblasts. These changes apparently resulted from reduced development of the lingual part of the enamel organ and might be correlated with a possible heterogeneity in the development of the enamel organ, as demonstrated for upper incisors. Our observations suggest independent development of the labial and lingual parts of the cervical loop. Furthermore, it appeared that the consequences of Ta mutation could not be interpreted only as a delay in tooth development.

Animals↗
PubMed1999

Morphogenesis of the lower incisor in the mouse from the bud to early bell stage.

The development of the lower incisor in the mouse was investigated from histological sections using computer-aided 3D reconstructions. At ED 13.0, the incisor was still at the bud stage. At ED 13.5, the initial cap was delimited by a short cervical loop, the development of which proceeded on the labial side, but was largely retarded on the medial side. This difference was maintained up to ED 15.0. From ED 16.0, the bell stage was achieved. Metaphases had a ubiquitous distribution both in the enamel organ and in the dental papilla from the bud to early bell stage. Apoptosis gradually increased in the mesenchyme posteriorly to the labial cervical loop from ED 13.5 to 14.0 and then disappeared; this apoptosis was not related to the posterior growth of the incisor. From ED 13.5, a high apoptotic activity was observed in the stalk. A focal area of apoptosis was observed at ED 13.5 in the enamel organ, approaching the epithelio-mesenchymal junction at the future tip of the incisor. There, the inner dental epithelium formed a bulbous protrusion towards dental papilla, reminiscent of the secondary enamel knot of mouse molars. This epithelial protrusion was still maintained at the bell stage. The enamel knot in the incisor demonstrated specific features, different from those characterizing the enamel knot in the molar: the concentric arrangement of epithelial cells was much less prominent and the occurrence of apoptosis was very transitory in the incisor at ED 13.5. The disappearance of the enamel knot despite a low apoptotic activity and the maintenance of the protrusion suggested a histological reorganization specific for rodent incisor.

Animals↗
PubMed1998

Expression and localization of laminin-5 subunits during mouse tooth development.

Tooth morphogenesis is regulated by epithelial-mesenchymal interactions mediated by the basement membrane (BM). Laminins are major glycoprotein components of the BMs, which are involved in several cellular activities. The expression and localization of the alpha3, beta3, and gamma2 laminin-5 subunits have been analyzed by in situ hybridization and immunohistochemistry during mouse molar development. Initially (E12), mRNAs of all subunits were detected in the entire dental epithelium and the corresponding proteins were located in the BM. During cap formation (E13-14), transcripts for the alpha3 and gamma2 subunits were localized in the outer dental epithelium (ODE), whereas the beta3 subunit mRNA was present in the inner dental epithelium (IDE). During the early bell stage (E16), immunoreactivity for all subunits disappeared from the BM along the IDE, although intense signals for beta3 mRNA were detectable in cells of the IDE. Subsequently, when the dentinal matrix was secreted by odontoblasts (E18-19.5), mRNAs of all three subunits were re-expressed by ameloblasts, and the corresponding proteins were detected in ameloblasts and in the enamel matrix. Tissue recombination experiments demonstrated that when E16 IDE or ODE was associated with E18 dental papilla mesenchyme, immunostaining for all laminin-5 subunits disappeared from the BM, whereas when cultured with non-dental limb bud mesenchyme, they remained positive after 48 hr of culture. These results suggest that the temporospatial expression of laminin-5 subunits in tooth development, which appears to be differentially controlled by the dental mesenchyme, might be related to the enamel organ histo-morphogenesis and the ameloblast differentiation.

Ameloblasts↗
PubMed1998

Expression and localization of laminin-5 subunits in the mouse incisor.

Laminin-5 is associated with several epithelial tissues and forms part of the anchoring filaments of hemidesmosomes. Recent data have shown that the expression of laminin-5 subunits is impaired in junctional epidermolysis bullosa (JEB), and, in these patients, enamel hypoplasia is commonly observed. Rodent incisors are continuously growing teeth with an asymmetry between their labial and lingual sides. Enamel matrix formation is restricted to the labial side. We have analyzed the changes in the expression and localization of laminin-5 subunits (alpha3, beta3, and gamma2) in lower incisors of the mouse. The apical loop located at the end of the labial side contained stem cells and showed expression for all laminin-5 subunits. In the anterior direction, the inner dental epithelial cells (IDE) transiently lost the immunoreactivity for all subunits, whereas the transcripts for the beta3 subunit remained in the IDE. All subunit mRNAs and proteins were expressed in ameloblasts facing predentine and also in secretory and maturation stage ameloblasts. Enamel matrix contained laminin-5. On the lingual side, the expression of laminin-5 subunits was continuous from the epithelial root sheath to the epithelial rests of Malassez in the periodontal ligament. These results suggest that spatial and temporal regulation of laminin-5 subunits correlates with the histogenesis of the dental organ, ameloblast differentiation, and enamel formation and also that laminin-5 plays a role in the adhesion between dental epithelial cells and the extracellular matrix (enamel or dentine) in areas where the dental basement membrane is absent.

Amelogenesis↗
PubMed1998

Correlation between apoptosis distribution and BMP-2 and BMP-4 expression in vestigial tooth primordia in mice.

The eutherian dental formula consists of three incisors, one canine, four premolars and three molars in each dental quadrant. Muroid evolution led to a reduction in the number of teeth, with one incisor separated from three molars by a long diastema. However, seven vestigial tooth primordia (D1-5, R1-2) have been detected in the embryonic diastemal area of the mouse maxilla between embryonic days (ED) 12.5 and 13.5. Computer-aided 3D reconstructions were used to analyse the temporo-spatial pattern of apoptosis during regression in the two largest and most distal vestiges (R1, R2). These structures have been widely considered as the primordium of the first upper molar and, accordingly, related molecular data have been interpreted exclusively in terms of progressive molar development. The spatial distribution of epithelial apoptosis, which affected the R1 and R2 rudiments in two consecutive waves on ED 12.5 and 13.5, respectively, was compared with our earlier data on expression of genes encoding bone morphogenetic proteins (BMP-2 and BMP-4). Similar temporo-spatial patterns of apoptosis and expression of BMP, specifically confined to the epithelium of the rudimentary tooth primordia, strongly support involvement of BMPs in the regulation of epithelial apoptosis during odontogenesis.

Animals↗
PubMed1998

Localization of antigens associated with adherens junctions, desmosomes, and hemidesmosomes during murine molar morphogenesis.

Epitheliomesenchymal interactions are known to play a crucial role during odontogenesis. Since epithelial cell-cell and cell-matrix interactions may also be involved in enamel organ histomorphogenesis, we investigated the localization of proteins associated with junctional complexes in mouse and rat first lower molars by indirect immunofluorescence. Adherens junctions were detected using antibodies directed against E-cadherin, beta-catenin, and plakoglobin (gamma-catenin). Desmosomes were localized with antibodies against desmoglein, and hemidesmosomes using antibodies against BP-230 and HD-1 proteins. When the inner dental epithelium differentiates, a decrease of E-cadherin, plakoglobin, and BP-230 is seen. An asymmetric distribution of plakoglobin, desmoglein, and BP-230 between the lateral and medial side of the tooth exists; desmoglein, which was first restricted to the gubernaculum dentis, progressively accumulated in the stellate reticulum, the stratum intermedium, and the basal pole of ameloblasts. The specific temporospatial distributions patterns of these antigens suggests a direct involvement of adherens junctions, desmosomes, and hemidesmosomes in the development of the murine first lower molar.

Animals↗
PubMed1998

Early stages of tooth morphogenesis in mouse analyzed by 3D reconstructions.

Computer-aided 3D reconstructions were used to investigate early odontogenesis in the ICR mouse, from the dental lamina to the cap stage. The diastemal region of the maxilla was not an empty zone: five transient epithelial rudiments (D1-D5) were found between ED 12.5-13.5. Two further rudiments (R1 and R2) were observed between D5 and the maxillary first molar primordium, whose bud emerged at ED 13.5. These rudiments might be related to vestiges of ancestral teeth. During this period, only an epithelial lamina was observed in front of the bud-shaped molar epithelium in the cheek region of the mandible. Apoptosis plays an important role in the reduction of antemolar rudiments in the maxilla and in the remodeling of the epithelium anterior to the M1 bud and cap in both jaws: two successive waves of apoptosis were detected in the mandible and in the maxilla. Computer-aided 3D reconstructions clearly demonstrated that morphologically different developmental stages coexist along the anteroposterior axis of M1 in both jaws.

Animals↗