Published online in Wiley InterScience (www.interscience.wiley. com)

ABSTRACT The mouse incisor has two unusual features: it grows continuously and it is covered by enamel exclusively on the labial side. The continuous growth is driven in part by epithelial stem cells in the cervical loop region that can both self-renew and give rise to ameloblasts. We have previously reported that ectopic enamel is found on the lingual side of the incisor in mice with loss-of-function of sprouty (spry) genes. Spry2 1/À ; Spry4 À/À mice, in which three sprouty alleles have been inactivated, have ectopic enamel as a result of upregulation of epithelial-mesenchymal FGF signaling in the lingual part of the cervical loop. Interestingly, lingual enamel is also present in the early postnatal period in Spry4 À/À mice, in which only two sprouty alleles have been inactivated, but ectopic enamel is not found in adults of this genotype. To explore the mechanisms underlying the disappearance of lingual enamel in Spry4 À/À adults, we studied the fate of the lingual enamel in Spry4 À/À mice by comparing the morphology and growth of their lower incisors with wild type and Spry2 1/À ; Spry4 À/À mice at several timepoints between the perinatal period and adulthood. Ameloblasts and enamel were detected on the lingual side in postnatal Spry2 1/À ; Spry4 1/À incisors. By contrast, new ectopic ameloblasts ceased to differentiate after postnatal day 3 in Spry4 À/À incisors, which was followed by a progressive loss of lingual enamel. Both the posterior extent of lingual enamel and the time of its last deposition were variable early postnatally in Spry4 À/À incisors, but in all Spry4 À/À adult incisors the lingual enamel was ultimately lost through continuous growth and abrasion of the incisor

Regulators of Collagen Fibrillogenesis during Molar Development in the Mouse

Development of mammalian teeth and surrounding tissues includes time–space changes in the extracellular matrix composition and organization. This requires complex control mechanisms to regulate its synthesis and remodeling. Fibril-associated collagens with interrupted triple helices (FACITs) and a group of small leucine-rich proteoglycans (SLRPs) are involved in the regulation of collagen fibrillogenesis. Recently, collagen type XII and collagen type XIV, members of the FACITs family, were found in the peridental mesenchyme contributing to alveolar bone formation. This study was designed to follow temporospatial expression of collagen types XIIa and XIVa in mouse first molar and adjacent tissues from embryonic day 13, when the alveolar bone becomes morphologically apparent around the molar tooth bud, until postnatal day 22, as the posteruption stage. The patterns of decorin, biglycan, and fibromodulin, all members of the SLRPs family and interacting with collagens XIIa and XIVa, were investigated simultaneously. The situation in the tooth was related to what happens in the alveolar bone, and both were compared to the periodontal ligament. The investigation provided a complex localization of the five antigens in soft tissues, the dental pulp, and periodontal ligaments; in the mineralized tissues, predentin/dentin and alveolar bone; and junction between soft and hard tissues. The results illustrated developmentally regulated and tissue-specific changes in the balance of the two FACITs and three SLRPs

ETUDE DE L'EXPRESSION DE MOLECULES D'ADHESION ET DE SONIC HEDGEHOG AU COURS DE L'HISTO-MORPHOGENESE DE L'INCISIVE INFERIEURE DE SOURIS

L'INCISIVE DE SOURIS EST CARACTERISEE PAR SA CROISSANCE CONTINUE SELON UN AXE ANTERO-POSTERIEUR ET PAR UNE ASYMETRIE FONCTIONNELLE : L'EMAIL N'EST PRESENT QUE SUR LA FACE LABIALE DE LA DENT. NOUS AVONS ETUDIE PAR RECONSTRUCTIONS 3D LE DEVELOPPEMENT DE L'INCISIVE INFERIEURE DEPUIS LE STADE DU BOURGEON JUSQU'AU STADE DE LA CLOCHE. LE DEVELOPPEMENT DES PARTIES LABIALE ET LINGUALE DE LA LEVRE CERVICALE (LC) PRESENTE DES ASYMETRIES DES LE STADE DU CAPUCHON : LA PARTIE LINGUALE EST EN RETARD PAR RAPPORT A LA PARTIE LABIALE ET IL Y A UN RETARD DE FERMETURE DE LA LC DU COTE MEDIAL. LA LOCALISATION D'ANTIGENES ASSOCIES AUX JONCTIONS CELLULE-CELLULE (E-CADHERINE, PLAKOGLOBINE, DESMOGLEINE), AUX INTERACTIONS CELLULE-MATRICE (SOUS-UNITE 6 DE L'INTEGRINE ET BP230) ET DE LA LAMININE 5 CONFIRME UNE DYNAMIQUE CELLULAIRE PLUS IMPORTANTE DANS LA PARTIE LABIALE DE LA LC. LORS DE LA TRANSITION CAPUCHON-CLOCHE, DES DESMOSOMES STABILISENT LA PARTIE ANTERIEURE DE L'ORGANE DE L'EMAIL. LE NUD DE L'EMAIL (NE), STRUCTURE EPITHELIALE TRANSITOIRE COMPOSEE DE CELLULES HORS-CYCLE, EST IMPLIQUE DANS LA SIGNALISATION DU DEVELOPPEMENT DENTAIRE. LE NE DE L'INCISIVE DIFFERE DE CELUI DE LA MOLAIRE CAR IL PRESENTE UN ARRANGEMENT HISTOLOGIQUE BEAUCOUP MOINS MARQUE, TRES PEU D'APOPTOSES ET UNE DUREE DE VIE PLUS COURTE. CONTRAIREMENT A CELLES DE LA MOLAIRE, LES CELLULES DU NE DE L'INCISIVE EXPRIMENT LA SOUS-UNITE 6 DE L'INTEGRINE ET INTERAGISSENT AVEC UNE MEMBRANE BASALE (MB) RICHE EN LAMININE 5. LA LAMININE 5 POUVANT INTERVENIR DANS L'ANCRAGE DES CELLULES EPITHELIALES, CES FAITS POURRAIENT ETRE MIS EN CORRELATION AVEC L'EXISTENCE D'UNE SEGREGATION DES CELLULES DU NE DE LA MOLAIRE QUE L'ON NE RETROUVE PAS DANS L'INCISIVE. LE GENE SHH CODE POUR UNE MOLECULE DE SIGNALISATION IMPLIQUEE DANS LA MORPHOGENESE DENTAIRE. L'HYBRIDATION IN SITU MONTRE UNE EXPRESSION ASYMETRIQUE DE SHH : SEULES LES CELLULES DE L'EPITHELIUM DENTAIRE INTERNE (EDI) DU COTE LABIAL L'EXPRIMENT, DU STADE CAPUCHON AU STADE CLOCHE. UNE ETUDE IN VITRO SUGGERE UN ROLE DE SHH DANS L'HISTOGENESE DE L'EDI. DES BILLES PREINCUBEES EN PRESENCE DE SHH MISES EN CONTACT DE LA PARTIE LINGUALE DE L'INCISIVE CONDUISENT A LA FORMATION DE PLIS DE L'EDI LINGUAL. CECI N'IMPLIQUE PAS DE PROLIFERATION CELLULAIRE LOCALISEE MAIS RESULTE D'UNE REORGANISATION CELLULAIRE.STRASBOURG-Sc. et Techniques (674822102) / SudocSudocFranceF

Regulators of Collagen Fibrillogenesis during Molar Development in the Mouse

Development of mammalian teeth and surrounding tissues includes time-space changes in the extracellular matrix composition and organization. This requires complex control mechanisms to regulate its synthesis and remodeling. Fibril-associated collagens with interrupted triple helices (FACITs) and a group of small leucine-rich proteoglycans (SLRPs) are involved in the regulation of collagen fibrillogenesis. Recently, collagen type XII and collagen type XIV, members of the FACITs family, were found in the peridentalmesenchyme contributing to alveolar bone formation. This study was designed to follow temporospatial expression of collagen types XIIa and XIVa in mouse first molar and adjacent tissues from embryonic day 13, when the alveolar bone becomes morphologically apparent around the molar tooth bud, until postnatal day 22, as the posteruption stage. The patterns of decorin, biglycan, and fibromodulin, all members of the SLRPs family and interacting with collagens XIIa and XIVa, were investigated simultaneously. The situation in the tooth was related to what happens in the alveolar bone, and both were compared to the periodontal ligament. The investigation provided a complex localization of the five antigens in soft tissues, the dental pulp, and periodontal ligaments; in the mineralized tissues, predentin/dentin and alveolar bone; and junction between soft and hard tissues. The results illustrated developmentally regulated and tissue-specific changes in the balance of the two FACITs and three SLRPs

Caspase-1 Inhibition Impacts the Formation of Chondrogenic Nodules, and the Expression of Markers Related to Osteogenic Differentiation and Lipid Metabolism

Caspase-1, as the main pro-inflammatory cysteine protease, was investigated mostly with respect to inflammation-related processes. Interestingly, caspase-1 was identified as being involved in lipid metabolism, which is extremely important for the proper differentiation of chondrocytes. Based on a screening investigation, general caspase inhibition impacts the expression of Cd36 in chondrocytes, the fatty acid translocase with a significant impact on lipid metabolism. However, the engagement of individual caspases in the effect has not yet been identified. Therefore, the hypothesis that caspase-1 might be a candidate here appears challenging. The primary aim of this study thus was to find out whether the inhibition of caspase-1 activity would affect Cd36 expression in a chondrogenic micromass model. The expression of Pparg, a regulator Cd36, was examined as well. In the caspase-1 inhibited samples, both molecules were significantly downregulated. Notably, in the treated group, the formation of the chondrogenic nodules was apparently disrupted, and the subcellular deposition of lipids and polysaccharides showed an abnormal pattern. To further investigate this observation, the samples were subjected to an osteogenic PCR array containing selected markers related to cartilage/bone cell differentiation. Among affected molecules, Bmp7 and Gdf10 showed a significantly increased expression, while Itgam, Mmp9, Vdr, and Rankl decreased. Notably, Rankl is a key marker in bone remodeling/homeostasis and thus is a target in several treatment strategies, including a variety of fatty acids, and is balanced by its decoy receptor Opg (osteoprotegerin). To evaluate the effect of Cd36 downregulation on Rankl and Opg, Cd36 silencing was performed using micromass cultures. After Cd36 silencing, the expression of Rankl was downregulated and Opg upregulated, which was an inverse effect to caspase-1 inhibition (and Cd36 upregulation). These results demonstrate new functions of caspase-1 in chondrocyte differentiation and lipid metabolism-related pathways. The effect on the Rankl/Opg ratio, critical for bone maintenance and pathology, including osteoarthritis, is particularly important here as well

Early development of the lower deciduous dentition and oral vestibule in human embryos.

The aim of this work was to investigate the early development of the deciduous dentition and oral vestibule in the human embryonic lower jaw. Histological sections and three-dimensional reconstructions from prenatal weeks 6-9 were used. A continuous anlage for the oral vestibule did not exist in the mandible. In contrast to the upper jaw, where we previously observed that the dental and vestibular epithelia developed separately, two dento-vestibular bulges differentiated in the incisor region of the mandible. The lingual parts of each bulge were found to give rise to the respective central and lateral incisors, whereas the labial parts differentiated into the vestibular epithelium. In the canine and molar areas, the dental and vestibular epithelia originated separately. Later, the segments of the vestibular epithelium fused into the labial vestibular ridge, giving rise to the lower oral vestibule in the lip region. In the cheek region, the oral vestibule was found to originate in the mucosal inflection between the developing jaw and the cheek. A similar heterogeneous developmental base for the oral vestibule was also observed in the upper jaw. There is thus no general scheme for the early development of the dental and vestibular epithelia that applies to both the upper and lower jaws, and to both their anterior and posterior regions

Impact of FasL Stimulation on Sclerostin Expression and Osteogenic Profile in IDG-SW3 Osteocytes

The Fas ligand (FasL) is known from programmed cell death, the immune system, and recently also from bone homeostasis. As such, Fas signalling is a potential target of anti-osteoporotic treatment based on the induction of osteoclastic cell death. Less attention has been paid to osteocytes, although they represent the majority of cells within the mature bone and are the key regulators. To determine the impact of FasL stimulation on osteocytes, differentiated IDG-SW3 cells were challenged by FasL, and their osteogenic expression profiles were evaluated by a pre-designed PCR array. Notably, the most downregulated gene was the one for sclerostin, which is the major marker of osteocytes and a negative regulator of bone formation. FasL stimulation also led to significant changes (over 10-fold) in the expression of other osteogenic markers: Gdf10, Gli1, Ihh, Mmp10, and Phex. To determine whether these alterations involved caspase-dependent or caspase-independent mechanisms, the IDG-SW3 cells were stimulated by FasL with and without a caspase inhibitor: Q-VD-OPh. The alterations were also detected in the samples treated by FasL along with Q-VD-OPh, pointing to the caspase-independent impact of FasL stimulation. These results contribute to an understanding of the recently emerging pleiotropic effects of Fas/FasL signalling and specify its functions in bone cells