The temporomandibular joint (TMJ) is one of the most used joints in the body. Defects and wear in the cartilage of the joint, condyle, and fibrocartilage disc lie at the heart of many common TMJ disorders. During postnatal development, the condyle acts as a growth center for the mandible, with cells moving as a conveyor belt away from the top of the condyle as they differentiate. The superficial layers of the condyle have been proposed to contain stem/progenitor populations to allow growth and maintain homeostasis. Here we have focused on the role of fibroblast-specific protein 1 (FSP1; also known as S100a4) as a key fibroblast stem/progenitor marker for the condyle. Lineage tracing with FSP1-Cre;R26RmTmG mice revealed that FSP1-expressing cells were restricted to the superficial fibroblast zone, giving rise to all layers of the condyle over time. The FSP1-expressing cells overlapped with other putative stem cell markers of the condyle, such as Gli1 and scleraxis. BrdU pulse chase experiments highlighted that a subset of FSP1 fibrocartilage was label retaining, suggesting that FSP1 labels a novel stem/progenitor cell population in the condyle. Destruction of FSP1-expressing cells by conditional diphtheria toxin activity in FSP1-Cre;R26RDTA mice resulted in severe TMJ osteoarthritis with loss of the cartilage structure. Lgr5-expressing cells in the superficial layer of the condyle have been shown to create a Wnt inhibitory niche. FSP1 expression postnatally was associated with a reduction in canonical Wnt activity in the condyle. Importantly, constitutive activation of Wnt/β catenin in FSP1-expressing cells led to a downregulation of FSP1 and progressive postnatal loss of TMJ condylar hyaline cartilage due to loss of the superficial stem/progenitor cells. These data demonstrate a novel role for FSP1-expressing cells in the superficial zone in growth and maintenance of the TMJ condylar cartilage and highlight the importance of regulating Wnt activity in this population.

• Keywords
• Wnt signaling, condyle, fibrocartilage, osteoarthritis, stem cell, temporomandibular disorders,
• MeSH
• Fibroblasts metabolism   MeSH
• Homeostasis physiology   MeSH
• Stem Cells * metabolism   physiology   MeSH
• Mice, Transgenic MeSH
• Mice MeSH
• Mandibular Condyle growth & development   cytology   metabolism   MeSH
• S100 Calcium-Binding Protein A4 * metabolism   physiology   MeSH
• Temporomandibular Joint * growth & development   cytology   MeSH
• Animals MeSH
• Check Tag
• Mice MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Lgr5 protein, mouse MeSH Browser
• Receptors, G-Protein-Coupled MeSH
• S100 Calcium-Binding Protein A4 * MeSH
• S100a4 protein, mouse MeSH Browser

Hypoxia is relevant to several physiological and pathological processes and this also applies for the tooth. The adaptive response to lowering oxygen concentration is mediated by hypoxia-inducible factors (HIFs). Since HIFs were shown to participate in the promotion of angiogenesis, stem cell survival, odontoblast differentiation and dentin formation, they may play a beneficial role in the tooth reparative processes. Although some data were generated in vitro, little is known about the in vivo context of HIFs in tooth development. In order to contribute to this field, the mouse mandibular first molar was used as a model.The expression and in situ localisation of HIFs were examined at postnatal (P) days P0, P7, P14, using RT-PCR and immunostaining. The expression pattern of a broad spectrum of hypoxia-related genes was monitored by customised PCR Arrays. Metabolic aspects were evaluated by determination of the lactate level and mRNA expression of the mitochondrial marker Nd1.The results show constant high mRNA expression of Hif1a, increasing expression of Hif2a, and very low expression of Hif3a during early postnatal molar development. In the examined period the localisation of HIFs in the nuclei of odontoblasts and the subodontoblastic layer identified their presence during odontoblastic differentiation. Additionally, the lower lactate level and higher expression of mitochondrial Nd1 in advanced development points to decreasing glycolysis during differentiation. Postnatal nuclear localisation of HIFs indicates a hypoxic state in specific areas of dental pulp as oxygen demands depend on physiological events such as crown and root dentin mineralization.

• Keywords
• Dental pulp, Development, Hypoxia-inducible factors, In vivo,
• MeSH
• Hypoxia-Inducible Factor 1, alpha Subunit * metabolism   genetics   MeSH
• Metabolic Networks and Pathways MeSH
• Molar * metabolism   growth & development   MeSH
• Mice MeSH
• Odontoblasts metabolism   MeSH
• Apoptosis Regulatory Proteins MeSH
• Repressor Proteins MeSH
• Basic Helix-Loop-Helix Transcription Factors * metabolism   genetics   MeSH
• Gene Expression Regulation, Developmental MeSH
• Dental Pulp * metabolism   MeSH
• Animals MeSH
• Check Tag
• Mice MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• endothelial PAS domain-containing protein 1 MeSH Browser
• Hypoxia-Inducible Factor 1, alpha Subunit * MeSH
• Hif1a protein, mouse MeSH Browser
• Hif3a protein, mouse MeSH Browser
• Apoptosis Regulatory Proteins MeSH
• Repressor Proteins MeSH
• Basic Helix-Loop-Helix Transcription Factors * MeSH

The development of a tooth germ in a precise size, shape, and position in the jaw, involves meticulous regulation of cell proliferation and cell death. Apoptosis, as the most common type of programmed cell death during embryonic development, plays a number of key roles during odontogenesis, ranging from the budding of the oral epithelium during tooth initiation, to later tooth germ morphogenesis and removal of enamel knot signaling center. Here, we summarize recent knowledge about the distribution and function of apoptotic cells during odontogenesis in several vertebrate lineages, with a special focus on amniotes (mammals and reptiles). We discuss the regulatory roles that apoptosis plays on various cellular processes during odontogenesis. We also review apoptosis-associated molecular signaling during tooth development, including its relationship with the autophagic pathway. Lastly, we cover apoptotic pathway disruption, and alterations in apoptotic cell distribution in transgenic mouse models. These studies foster a deeper understanding how apoptotic cells affect cellular processes during normal odontogenesis, and how they contribute to dental disorders, which could lead to new avenues of treatment in the future.

• Keywords
• apoptosis, dental lamina, morphogenesis, odontogenesis, teeth,
• Publication type
• Journal Article MeSH
• Review MeSH

Within the mandible, the odontogenic and osteogenic mesenchymes develop in a close proximity and form at about the same time. They both originate from the cranial neural crest. These two condensing ecto-mesenchymes are soon separated from each other by a very loose interstitial mesenchyme, whose cells do not express markers suggesting a neural crest origin. The two condensations give rise to mineralized tissues while the loose interstitial mesenchyme, remains as a soft tissue. This is crucial for proper anchorage of mammalian teeth. The situation in all three regions of the mesenchyme was compared with regard to cell heterogeneity. As the development progresses, the early phenotypic differences and the complexity in cell heterogeneity increases. The differences reported here and their evolution during development progressively specifies each of the three compartments. The aim of this review was to discuss the mechanisms underlying condensation in both the odontogenic and osteogenic compartments as well as the progressive differentiation of all three mesenchymes during development. Very early, they show physical and structural differences including cell density, shape and organization as well as the secretion of three distinct matrices, two of which will mineralize. Based on these data, this review highlights the consecutive differences in cell-cell and cell-matrix interactions, which support the cohesion as well as mechanosensing and mechanotransduction. These are involved in the conversion of mechanical energy into biochemical signals, cytoskeletal rearrangements cell differentiation, or collective cell behavior.

• Keywords
• condensation, development, mandible, mesenchyme, mouse, odontogenesis, osteogenesis,
• Publication type
• Journal Article MeSH
• Review MeSH

The Eda pathway ( Eda, Edar, Edaradd) plays an important role in tooth development, determining tooth number, crown shape, and enamel formation. Here we show that the Eda pathway also plays a key role in root development. Edar (the receptor) is expressed in Hertwig's epithelial root sheath (HERS) during root development, with mutant mice showing a high incidence of taurodontism: large pulp chambers lacking or showing delayed bifurcation or trifurcation of the roots. The mouse upper second molars in the Eda pathway mutants show the highest incidence of taurodontism, this enhanced susceptibility being matched in human patients with mutations in EDA-A1. These taurodont teeth form due to defects in the direction of extension of the HERS from the crown, associated with a more extensive area of proliferation of the neighboring root mesenchyme. In those teeth where the angle at which the HERS extends from the crown is very wide and therefore more vertical, the mutant HERSs fail to reach toward the center of the tooth in the normal furcation region, and taurodont teeth are created. The phenotype is variable, however, with milder changes in angle and proliferation leading to normal or delayed furcation. This is the first analysis of the role of Eda in the root, showing a direct role for this pathway during postnatal mouse development, and it suggests that changes in proliferation and angle of HERS may underlie taurodontism in a range of syndromes.

• Keywords
• ectodermal dysplasia, ectodysplasins, epithelium, furcation defects, periodontium, tooth,
• MeSH
• Tooth Abnormalities genetics   MeSH
• Child MeSH
• Ectodysplasins genetics   MeSH
• Phenotype MeSH
• Dental Pulp Cavity abnormalities   MeSH
• Humans MeSH
• Adolescent MeSH
• Molar abnormalities   embryology   MeSH
• Mice MeSH
• Odontogenesis genetics   MeSH
• X-Ray Microtomography MeSH
• Signal Transduction MeSH
• Tooth Root abnormalities   embryology   MeSH
• Animals MeSH
• Check Tag
• Child MeSH
• Humans MeSH
• Adolescent MeSH
• Male MeSH
• Mice MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• EDA protein, human MeSH Browser
• Eda protein, mouse MeSH Browser
• Ectodysplasins MeSH

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.

• Keywords
• FACITs, SLRPs, alveolar bone, collagen, odontogenesis,
• Publication type
• Journal Article MeSH

Caspase-3 and -7 are generally known for their central role in the execution of apoptosis. However, their function is not limited to apoptosis and under specific conditions activation has been linked to proliferation or differentiation of specialised cell types. In the present study, we followed the localisation of the activated form of caspase-7 during intramembranous (alveolar and mandibular bones) and endochondral (long bones of limbs) ossification in mice. In both bone types, the activated form of caspase-7 was detected from the beginning of ossification during embryonic development and persisted postnatally. The bone status was investigated by microCT in both wild-type and caspase-7-deficient adult mice. Intramembranous bone in mutant mice displayed a statistically significant decrease in volume while the mineral density was not altered. Conversely, endochondral bone showed constant volume but a significant decrease in mineral density in caspase-7 knock-out mice. Cleaved caspase-7 was present in a number of cells that did not show signs of apoptosis. PCR array analysis of the mandibular bone of caspase-7-deficient versus wild-type mice pointed to a significant decrease in mRNA levels for Msx1 and Smad1 in early bone formation. These observations might explain the decrease in the alveolar bone volume of adult knock-out mice. In conclusion, this study is the first to report a non-apoptotic function of caspase-7 in osteogenesis and also demonstrates further specificities in endochondral versus intramembranous ossification.

• MeSH
• Apoptosis MeSH
• Embryonic Development MeSH
• Caspase 3 metabolism   MeSH
• Caspase 7 genetics   metabolism   MeSH
• Bone and Bones diagnostic imaging   metabolism   pathology   MeSH
• Mice, Knockout MeSH
• Mice MeSH
• Osteogenesis * MeSH
• Osteocalcin metabolism   MeSH
• Tomography, X-Ray Computed MeSH
• Smad1 Protein genetics   metabolism   MeSH
• MSX1 Transcription Factor genetics   metabolism   MeSH
• Animals MeSH
• Check Tag
• Mice MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Caspase 3 MeSH
• Caspase 7 MeSH
• Msx1 protein, mouse MeSH Browser
• Osteocalcin MeSH
• Smad1 Protein MeSH
• MSX1 Transcription Factor MeSH

Apoptosis is an important morphogenetic event in embryogenesis as well as during postnatal life. In the last 2 decades, apoptosis in tooth development (odontogenesis) has been investigated with gradually increasing focus on the mechanisms and signaling pathways involved. The molecular machinery responsible for apoptosis exhibits a high degree of conservation but also organ and tissue specific patterns. This review aims to discuss recent knowledge about apoptotic signaling networks during odontogenesis, concentrating on the mouse, which is often used as a model organism for human dentistry. Apoptosis accompanies the entire development of the tooth and corresponding remodeling of the surrounding bony tissue. It is most evident in its role in the elimination of signaling centers within developing teeth, removal of vestigal tooth germs, and in odontoblast and ameloblast organization during tooth mineralization. Dental apoptosis is caspase dependent and proceeds via mitochondrial mediated cell death with possible amplification by Fas-FasL signaling modulated by Bcl-2 family members.

• MeSH
• Apoptosis * MeSH
• Caspases genetics   metabolism   MeSH
• Humans MeSH
• Mice MeSH
• Odontogenesis * MeSH
• Signal Transduction * MeSH
• Tooth Germ cytology   embryology   metabolism   MeSH
• Animals MeSH
• Check Tag
• Humans MeSH
• Mice MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Review MeSH
• Names of Substances
• Caspases MeSH