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Ann Huysseune - One of the best experts on this subject based on the ideXlab platform.
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slow cycling cells in the continuous Dental Lamina of scyliorhinus canicula new evidence for stem cells in sharks
Developmental Biology, 2016Co-Authors: Sam Vandenplas, Robbe Vandeghinste, Agnes Boutet, Sylvie Mazan, Ann HuysseuneAbstract:In the lesser spotted catshark (Scyliorhinus canicula), as in most non-mammalian vertebrates, the dentition renews throughout life. To contribute to our understanding of how continuous tooth replacement is achieved, we searched for evidence for the presence of stem cells in this species. Three-dimensional reconstructions of juvenile (2–3 weeks post-hatch) specimens showed that tooth families merge imperceptibly with so-called interDental zones within a continuous and permanent Dental Lamina. InterDental regions are composed of three layers, continuous with cervical loop, middle, and outer Dental epithelium of the tooth families, respectively. A BrdU pulse-chase experiment revealed that cell proliferation is initiated in the lingual part of the Dental Lamina and the resulting population shifts one tooth position towards the oral epithelium in around four to five weeks. In the longest chase time (114 days) label-retaining and arguably non-differentiated cells were present at the lingual border of the Dental Lamina. These were found in the outer and middle Dental epithelium, both within and between tooth families. This area of the Dental Lamina did not show expression or distribution of Sox2. Our data support the hypothesis that stem cells reside at the lingual border of the continuous Dental Lamina, more specifically in the middle Dental epithelium at the level of the tooth families, and in its extension between the tooth families. To demonstrate their true stemness and their role in continuous tooth replacement, it remains to be shown that these cells have the potential to give rise to a complete new successor.
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Epithelial Label-Retaining Cells Are Absent during Tooth Cycling in Salmo salar and Polypterus senegalus.
PloS one, 2016Co-Authors: Sam Vandenplas, Maxime Willems, P. Eckhard Witten, Tom Hansen, Per Gunnar Fjelldal, Ann HuysseuneAbstract:The Atlantic salmon (Salmo salar) and African bichir (Polypterus senegalus) are both actinopterygian fish species that continuously replace their teeth without the involvement of a successional Dental Lamina. Instead, they share the presence of a middle Dental epithelium: an epithelial tier enclosed by inner and outer Dental epithelium. It has been hypothesized that this tier could functionally substitute for a successional Dental Lamina and might be a potential niche to house epithelial stem cells involved in tooth cycling. Therefore, in this study we performed a BrdU pulse chase experiment on both species to (1) determine the localization and extent of proliferating cells in the Dental epithelial layers, (2) describe cell dynamics and (3) investigate if label-retaining cells are present, suggestive for the putative presence of stem cells. Cells proliferate in the middle Dental epithelium, outer Dental epithelium and cervical loop at the lingual side of the Dental organ to form a new tooth germ. Using long chase times, both in S. salar (eight weeks) and P. senegalus (eight weeks and twelve weeks), we could not reveal the presence of label-retaining cells in the Dental organ. Immunostaining of P. senegalus Dental organs for the transcription factor Sox2, often used as a stem cell marker, labelled cells in the zone of outer Dental epithelium which grades into the oral epithelium (ODE transition zone) and the inner Dental epithelium of a successor only. The location of Sox2 distribution does not provide evidence for epithelial stem cells in the Dental organ and, more specifically, in the middle Dental epithelium. Comparison of S. salar and P. senegalus reveals shared traits in tooth cycling and thus advances our understanding of the developmental mechanism that ensures lifelong replacement.
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Tooth replacement without a Dental Lamina: The search for epithelial stem cells in Polypterus senegalus
Journal of experimental zoology. Part B Molecular and developmental evolution, 2014Co-Authors: Sam Vandenplas, Adelbert De Clercq, Ann HuysseuneAbstract:Most actinopterygians replace their teeth continuously throughout life. To address the question of where and how replacement teeth form in actinopterygians, it is advisable to investigate well-chosen representatives within the lineage. The African bichir, Polypterus senegalus, belongs to the earliest diverged group of the actinopterygian lineage with currently living representatives. Its well characterized dentition, together with its phylogenetic position, make this species an attractive model to answer following questions: (1) when and where does the replacement tooth form and how is it connected with the Dental organ of the predecessor, and (2) is there any evidence for the presence of epithelial stem cells, hypothesized to play a role in replacement? Serial sections show that one tooth family can contain up to three members, which are all interconnected by Dental epithelium. Replacement teeth develop without the presence of a successional Dental Lamina. We propose that this is the plesiomorphic condition for tooth replacement in actinopterygians. BrdU pulse-chase experiments reveal cells in the outer and middle Dental epithelium, proliferating at the time of initiation of a new replacement tooth. It is tempting to assume that these cell layers provide a stem cell niche. The observed absence of label-retaining cells after long chase times (up to 8 weeks) is held against the light of divergent views on cell cycling properties of stem cells. At present, our data do not support, neither reject, the hypothesis on involvement of epithelial stem cells within the process of continuous tooth replacement. J. Exp. Zool. (Mol. Dev. Evol.) 322B: 281–293, 2014. © 2014 Wiley Periodicals, Inc.
Sam Vandenplas - One of the best experts on this subject based on the ideXlab platform.
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slow cycling cells in the continuous Dental Lamina of scyliorhinus canicula new evidence for stem cells in sharks
Developmental Biology, 2016Co-Authors: Sam Vandenplas, Robbe Vandeghinste, Agnes Boutet, Sylvie Mazan, Ann HuysseuneAbstract:In the lesser spotted catshark (Scyliorhinus canicula), as in most non-mammalian vertebrates, the dentition renews throughout life. To contribute to our understanding of how continuous tooth replacement is achieved, we searched for evidence for the presence of stem cells in this species. Three-dimensional reconstructions of juvenile (2–3 weeks post-hatch) specimens showed that tooth families merge imperceptibly with so-called interDental zones within a continuous and permanent Dental Lamina. InterDental regions are composed of three layers, continuous with cervical loop, middle, and outer Dental epithelium of the tooth families, respectively. A BrdU pulse-chase experiment revealed that cell proliferation is initiated in the lingual part of the Dental Lamina and the resulting population shifts one tooth position towards the oral epithelium in around four to five weeks. In the longest chase time (114 days) label-retaining and arguably non-differentiated cells were present at the lingual border of the Dental Lamina. These were found in the outer and middle Dental epithelium, both within and between tooth families. This area of the Dental Lamina did not show expression or distribution of Sox2. Our data support the hypothesis that stem cells reside at the lingual border of the continuous Dental Lamina, more specifically in the middle Dental epithelium at the level of the tooth families, and in its extension between the tooth families. To demonstrate their true stemness and their role in continuous tooth replacement, it remains to be shown that these cells have the potential to give rise to a complete new successor.
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Epithelial Label-Retaining Cells Are Absent during Tooth Cycling in Salmo salar and Polypterus senegalus.
PloS one, 2016Co-Authors: Sam Vandenplas, Maxime Willems, P. Eckhard Witten, Tom Hansen, Per Gunnar Fjelldal, Ann HuysseuneAbstract:The Atlantic salmon (Salmo salar) and African bichir (Polypterus senegalus) are both actinopterygian fish species that continuously replace their teeth without the involvement of a successional Dental Lamina. Instead, they share the presence of a middle Dental epithelium: an epithelial tier enclosed by inner and outer Dental epithelium. It has been hypothesized that this tier could functionally substitute for a successional Dental Lamina and might be a potential niche to house epithelial stem cells involved in tooth cycling. Therefore, in this study we performed a BrdU pulse chase experiment on both species to (1) determine the localization and extent of proliferating cells in the Dental epithelial layers, (2) describe cell dynamics and (3) investigate if label-retaining cells are present, suggestive for the putative presence of stem cells. Cells proliferate in the middle Dental epithelium, outer Dental epithelium and cervical loop at the lingual side of the Dental organ to form a new tooth germ. Using long chase times, both in S. salar (eight weeks) and P. senegalus (eight weeks and twelve weeks), we could not reveal the presence of label-retaining cells in the Dental organ. Immunostaining of P. senegalus Dental organs for the transcription factor Sox2, often used as a stem cell marker, labelled cells in the zone of outer Dental epithelium which grades into the oral epithelium (ODE transition zone) and the inner Dental epithelium of a successor only. The location of Sox2 distribution does not provide evidence for epithelial stem cells in the Dental organ and, more specifically, in the middle Dental epithelium. Comparison of S. salar and P. senegalus reveals shared traits in tooth cycling and thus advances our understanding of the developmental mechanism that ensures lifelong replacement.
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Tooth replacement in an evo-devo context : the Dental Lamina as a possible source of stem cells
2016Co-Authors: Sam VandenplasAbstract:The enthralling ability to continuously replace teeth throughout life has fascinated scientists for decades. This ability (polyphyodonty) is maintained in almost all tooth-bearing non-mammalian vertebrates. Teeth are organised in tooth families, i.e. a functional tooth and all of its successors (Reif, 1982). In general, first and later generation teeth develop within an epithelial Dental Lamina as result of interaction of the epithelial cells with the underlying neural crest derived mesenchyme. Many aspects of tooth development and tooth evolution have been intensively studied over the past century; however the mechanism that drives lifelong tooth renewal remains largely unknown. Huysseune and Thesleff (2004) were the first to hypothesise that epithelial stem cells might be involved in this process, and suggested the Dental Lamina as a putative stem cell niche. In this thesis, we wished to test this hypothesis using a selection of polyphyodont species. In each of the species examined, we focussed on the lower jaw, and addressed three key issues: (1) the morphology and architecture of the Dental tissues, with a particular interest for the Dental Lamina, (2) the spatiotemporal pattern of cell proliferation within the different layers of the Dental Lamina, and (3) the potential presence of epithelial stem cells. We selected three polyphyodont species that are interesting from a comparative, evo-devo perspective: a chondrichthyan (Scyliorhinus canicula) and two actinopterygian osteichthyans (Polypterus senegalus as a member of a basal clade within the Actinopterygii and Salmo salar as a basal protacanthopterygian). (1) Scyliorhinus canicula has many successor teeth, which are prefabricated before the functional tooth is shed (CHAPTER 3). This results in tooth family sizes of seven to eight members. All tooth families are interconnected by a continuous and permanent Dental Lamina and are organised in an alternating pattern of developmental stages along the jaw margin. Three to four members of each family reside in the Dental Lamina. Polypterus senegalus and Salmo salar have their teeth organised in tooth families with two to three members; however, neither for the establishment of the first-generation tooth, nor for the development of its successors, a distinct Dental Lamina could be determined (CHAPTER 5,7). The maturation stage of functional teeth in Polypterus senegalus showed an alternating pattern, similar on both jaw halves (CHAPTER 4), while in Salmo salar a pattern with tooth families in similar developmental stages occurred every third position (CHAPTER 6). We propose to define the Dental Lamina in broad terms as ‘all epithelial cells that enclose a tooth family’. This allows us to interpret the Dental Lamina in Polypterus senegalus (CHAPTER 5) and Salmo salar (CHAPTER 7) as being extremely small or spatially compressed rather than being absent, and morphologically indistinguishable from the superficial epithelium. In conclusion of our morphological observations, we have constructed a hypothetical evolutionary model that generalises the Dental Lamina as a homologous modular structure in Dental development (CHAPTER 8). (2) BrdU proliferation studies showed dividing cells during the development of the youngest tooth germs in all three species (CHAPTERS 3,5,7). These tooth germs arise at the distal end of the Dental Lamina in Scyliorhinus canicula and the lingual side of the Dental Lamina in Polypterus senegalus and Salmo salar. In all three species, the middle Dental epithelium (MDE) and outer Dental epithelium (ODE) in the lingualmost part (i.e. most distal) of the Dental Lamina showed intensive proliferation, while the transition zone of the outer Dental epithelium towards the oral epithelium was not proliferating in any of the three species. Further similarities were obvious from BrdU chase experiments (CHAPTERS 3,5,7). All three species showed a shift in position of proliferative areas in the epithelium from the lingual side of the Dental Lamina towards a labial and oral position. This is consistent with a shift that developing successor teeth undergo towards the superficial epithelium, i.e. the location where they replace functional teeth. (3) BrdU pulse-chase experiments were conducted in all three species, with the intention to detect label-retaining cells (LRCs) in the Dental Lamina as a possible indication for the presence of stem cells. In Scyliorhinus canicula, LRCs were found in the lingualmost part of the Dental Lamina both within the Dental and interDental region (CHAPTER 3). Our experiments on Salmo salar and Polypterus senegalus did not reveal any of such cells in the epithelial tissues surrounding a tooth family (CHAPTERS 5,7). Immunohistological staining for Sox2, used on all three species as proxy for the potential presence of stem cells, yielded consistent results, with positive staining in the oral epithelium, taste buds and ODE transition zone but absent in the Dental Lamina (CHAPTERS 3,7). The Sox2+ cells in Scyliorhinus canicula did not coincide with the LRCs in the MDE. The combination of these conflicting results obtained for the three species studied, provided arguments for either of two scenarios: one supporting the presence, and one, conversely, in support of the absence of stem cells in the Dental Lamina. While only limited support for the presence of epithelial stem cells could be collected using the commonly proposed character of label retention, we consider the presence of cells with stem cell like characteristics likely. At the same time we emphasise that the concept of what ‘true’ stem cells are, needs to be critically re-evaluated. In the species examined, the lingualmost part of the MDE could serve as a site within the Dental Lamina to maintain a population of such potential stem cells. Continued experimental research on the proposed candidate area for stem cells should be pursued.
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Tooth replacement without a Dental Lamina: The search for epithelial stem cells in Polypterus senegalus
Journal of experimental zoology. Part B Molecular and developmental evolution, 2014Co-Authors: Sam Vandenplas, Adelbert De Clercq, Ann HuysseuneAbstract:Most actinopterygians replace their teeth continuously throughout life. To address the question of where and how replacement teeth form in actinopterygians, it is advisable to investigate well-chosen representatives within the lineage. The African bichir, Polypterus senegalus, belongs to the earliest diverged group of the actinopterygian lineage with currently living representatives. Its well characterized dentition, together with its phylogenetic position, make this species an attractive model to answer following questions: (1) when and where does the replacement tooth form and how is it connected with the Dental organ of the predecessor, and (2) is there any evidence for the presence of epithelial stem cells, hypothesized to play a role in replacement? Serial sections show that one tooth family can contain up to three members, which are all interconnected by Dental epithelium. Replacement teeth develop without the presence of a successional Dental Lamina. We propose that this is the plesiomorphic condition for tooth replacement in actinopterygians. BrdU pulse-chase experiments reveal cells in the outer and middle Dental epithelium, proliferating at the time of initiation of a new replacement tooth. It is tempting to assume that these cell layers provide a stem cell niche. The observed absence of label-retaining cells after long chase times (up to 8 weeks) is held against the light of divergent views on cell cycling properties of stem cells. At present, our data do not support, neither reject, the hypothesis on involvement of epithelial stem cells within the process of continuous tooth replacement. J. Exp. Zool. (Mol. Dev. Evol.) 322B: 281–293, 2014. © 2014 Wiley Periodicals, Inc.
Di-poï Nicolas - One of the best experts on this subject based on the ideXlab platform.
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Pogona vitticeps tooth transcriptomics
2019Co-Authors: Salomies Lotta, Eymann Julia, Khan Imran, Di-poï NicolasAbstract:Paired-end sequencing reads (Illumina technology) of successional Dental Lamina tissues of acrodont teeth from Pogona vitticeps lizard, biological replicate
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Pogona vitticeps tooth transcriptomics
2019Co-Authors: Salomies Lotta, Eymann Julia, Khan Imran, Di-poï NicolasAbstract:Paired-end sequencing reads (Illumina technology) of successional Dental Lamina tissues of pleurodont teeth from Pogona vitticeps lizard, biological replicate
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The alternative regenerative strategy of bearded dragon unveils the key processes underlying vertebrate tooth renewal
'eLife Sciences Publications Ltd', 2019Co-Authors: Salomies Lotta, Eymann Julia, Khan Imran, Di-poï NicolasAbstract:Deep understanding of tooth regeneration is hampered by the lack of lifelong replacing oral dentition in most conventional models. Here, we show that the bearded dragon, one of the rare vertebrate species with both polyphyodont and monophyodont teeth, constitutes a key model for filling this gap, allowing direct comparison of extreme dentition types. Our developmental and high-throughput transcriptomic data of microdissected Dental cells unveils the critical importance of successional Dental Lamina patterning, in addition to maintenance, for vertebrate tooth renewal. This patterning process happens at various levels, including directional growth but also gene expression levels, dynamics, and regionalization, and involves a large number of yet uncharacterized Dental genes. Furthermore, the alternative renewal mechanism of bearded dragon dentition, with dual location of slow-cycling cells, demonstrates the importance of cell migration and functional specialization of putative epithelial stem/progenitor niches in tissue regeneration, while expanding the diversity of Dental replacement strategies in vertebrates.Peer reviewe
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Data from: The alternative regenerative strategy of bearded dragon unveils the key processes underlying vertebrate tooth renewal
2019Co-Authors: Salomies Lotta, Eymann Julia, Khan Imran, Di-poï NicolasAbstract:Deep understanding of lifelong tooth replacement is hampered by the lack of polyphyodonty or oral dentition in conventional models. Here, we show that the bearded dragon, one of the rare vertebrate species with both polyphyodont and monophyodont teeth, constitutes a key model for filling this gap, allowing direct comparison of extreme dentition types. Our developmental and high-throughput transcriptomic data of microdissected Dental cells unveils the critical importance of successional Dental Lamina patterning, in addition to maintenance, for vertebrate tooth renewal. This patterning process happens at various levels, including directional growth but also gene expression levels, dynamics, and regionalization, and involves a large number of yet uncharacterized Dental genes. Furthermore, the alternative renewal mechanism of bearded dragon dentition, with dual location of slow-cycling cells, demonstrates the importance of cell migration and functional specialization of putative epithelial stem/progenitor niches in tissue regeneration, while expanding the diversity of Dental replacement strategies in vertebrates
Abigail S Tucker - One of the best experts on this subject based on the ideXlab platform.
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Dental Lamina morphology in monophyodont mouse.
2015Co-Authors: Hana Dosedělová, Abigail S Tucker, Hervé Lesot, Jana Dumková, Kristýna Glocová, Michaela Kunová, Iva Veselá, Pavel Krejčí, František Tichý, Aleš HamplAbstract:A: Dental Lamina in monophyodont mouse at E18 is composed of the Dental stalk area (ds) connecting the first lower molar (M1) to the oral epithelium and rudimental successional Dental Lamina (arrow). Dental stalk is very short and tooth develops in the close proximity to the oral epithelium. A´: Detail of Dental stalk area at E18. B: 3D reconstruction of the Dental stalk area as inclined view from rostral part. B´: Detail of continuous rudimental successional Dental Lamina (arrow) at E18. C: Lower power of the first molar and detail of the Dental stalk area (C´) at P2 with smaller successional Dental Lamina. D, D´: Rudimental successional Dental Lamina (arrow) is smaller at P2 especially at rostral and caudal end of the first molar (M1) as shown by 3D reconstruction. E, E´: Dental stalk area at P6. F, F´: The size of successional Dental Lamina is much smaller at P6 and it forms distinct structure just at cusps level (arrow). G, G´: The successional Lamina is protruding on the lingual aspect of the second molar (M2) at E18. H, H´: The rudimental successional Dental Lamina of M2 became smaller at P2 and P8 (I, I´). J, J´: In contrast to the first molar area, the Lamina is still visible close M2 at P10. K, K´: There is no successional Lamina close the third molar at P2 as the teeth reached just early cup stage. L, L´: In the area of the third molar (M3), successional Lamina was well visible at P8. M, M´: Later in development became thinner. N, N´: At P12, it was still observable at P12 in contrast to the first and the second molar area. arrow—rudimental successional Dental Lamina, oe—oral epithelium. Hematoxylin-Eosin. Scale bar—100 μm
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Rudimental successional Dental Lamina in the mouse.
2015Co-Authors: Hana Dosedělová, Abigail S Tucker, Hervé Lesot, Jana Dumková, Kristýna Glocová, Michaela Kunová, Iva Veselá, Pavel Krejčí, František Tichý, Aleš HamplAbstract:A-C: The successional Dental Lamina is visible from late embryonic stages (E16) as the epithelial thickening on the lingual side of the outer enamel epithelium. B: Cytokeratin-positive cells are located mostly in the Dental stalk area while epithelial thickening is less positive. C: PCNA-positive cells are located in the basal epithelial layer with higher appearance on the lingual side and in the epithelial thickening. D-F: Later in development at E18, the RSDL becomes separated from the tooth germ and forms large epithelial protrusion. The area of the RSDL is cytokeratin-negative (E) and PCNA-positive (F). G-I: Ultrastructure of the RSDL at E18 shows the evidence of several layers of epithelial cells (1) with reduced intercellular spaces (2). Flat mesenchymal cells surround the tip of the Lamina (3) together with small blood vessels (4). Folds of the epithelial cells (5) are located on the tip of the Lamina. Several macrophages (6) enclose the RSDL area. J-L: During early postnatal stage (P2), the successional Lamina is still well distinguishable epithelial structure. The area of the RSDL is cytokeratin-negative (K) and PCNA-positive (L). M-O: Ultrastructure of the RSDL at P2 reveals several layers of epithelial cells with smooth nuclear contours (1) and small intercellular spaces (2). Large folds of epithelial cells are located on the tip of the successional Dental Lamina (3) containing numerous lysosomes (5). Fibroblasts (4) exhibit cytoplasmatic processes closely to basement membrane surrounded by large amount of extracellular matrix (5). P-R: Later in development, the Lamina forms just rudimental thin epithelial projection. The area of the RSDL is cytokeratin-positive (Q) and only few PCNA-positive cells are located in this area (R). S-U: Ultrastructure of the RSDL at P8. Only leading epithelial cells contain nucleus with smooth contours (1) with a few organelles—mostly mitochondria (4). Other cells exhibit undulated nuclear envelope (3). Intercellular spaces between epithelial cells are still reduced (2). Proliferating cells are labeled by PCNA antibody (brown nuclei, arrows). Epithelial cells are labeled by cytokeratin antibody (brown cytoplasm). Negative cells are counterstained by Hematoxylin (blue nuclei).
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Fate of the Molar Dental Lamina in the Monophyodont Mouse
2015Co-Authors: Hana Dosedělová, Abigail S Tucker, Hervé Lesot, Jana Dumková, Kristýna Glocová, Michaela Kunová, Iva Veselá, Pavel Krejčí, František Tichý, Aleš HamplAbstract:The successional Dental Lamina (SDL) plays an essential role in the development of replacement teeth in diphyodont and polyphyodont animals. A morphologically similar structure, the rudimental successional Dental Lamina (RSDL), has been described in monophyodont (only one tooth generation) lizards on the lingual side of the developing functional tooth. This rudimentary Lamina regresses, which has been proposed to play a role in preventing the formation of future generations of teeth. A similar rudimentary lingual structure has been reported associated with the first molar in the monophyodont mouse, and we show that this structure is common to all murine molars. Intriguingly, a lingual Lamina is also observed on the non-replacing molars of other diphyodont mammals (pig and hedgehog), initially appearing very similar to the successional Dental Lamina on the replacing teeth. We have analyzed the morphological as well as ultrastructural changes that occur during the development and loss of this molar Lamina in the mouse, from its initiation at late embryonic stages to its disappearance at postnatal stages. We show that loss appears to be driven by a reduction in cell proliferation, down-regulation of the progenitor marker Sox2, with only a small number of cells undergoing programmed cell death. The lingual Lamina was associated with the Dental stalk, a short epithelial connection between the tooth germ and the oral epithelium. The Dental stalk remained in contact with the oral epithelium throughout tooth development up to eruption when connective tissue and numerous capillaries progressively invaded the Dental stalk. The buccal side of the Dental stalk underwent keratinisation and became part of the gingival epithelium, while most of the lingual cells underwent programmed cell death and the tissue directly above the erupting tooth was shed into the oral cavity.
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Organized Emergence of Multiple-Generations of Teeth in Snakes Is Dysregulated by Activation of Wnt/Beta-Catenin Signalling
PLOS ONE, 2013Co-Authors: Marcia Gaete, Abigail S TuckerAbstract:In contrast to mammals, most reptiles constantly regenerate their teeth. In the snake, the epithelial Dental Lamina ends in a successional Lamina, which proliferates and elongates forming multiple tooth generations, all linked by a permanent Dental Lamina. To investigate the mechanisms used to control the initiation of new tooth germs in an ordered sequential pattern we utilized the polyphodont (multiple-generation) corn snake (Pantherophis guttatus). We observed that the Dental Lamina expressed the transcription factor Sox2, a multipotent stem cell marker, whereas the successional Lamina cells expressed the transcription factor Lef1, a Wnt/β-catenin pathway target gene. Activation of the Wnt/β-catenin pathway in culture increased the number of developing tooth germs, in comparison to control untreated cultures. These additional tooth germs budded off from ectopic positions along the Dental Lamina, rather than in an ordered sequence from the successional Lamina. Wnt/β-catenin activation enhanced cell proliferation, particularly in normally non-odontogenic regions of the Dental Lamina, which widely expressed Lef1, restricting the Sox2 domain. This suggests an expansion of the successional Lamina at the expense of the Dental Lamina. Activation of the Wnt/β-catenin pathway in cultured snake Dental organs, therefore, led to changes in proliferation and to the molecular pattern of the Dental Lamina, resulting in loss of the organised emergence of tooth germs. These results suggest that epithelial compartments are critical for the arrangement of organs that develop in sequence, and highlight the role of Wnt/β-catenin signalling in such processes.
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Fate and expression pattern of the Dental Lamina in the snake.
2013Co-Authors: Marcia Gaete, Abigail S TuckerAbstract:(A–D) 10-day culture of the snake Dental organ labelled with DiI. (A, B, C) fluorescence microscopy and (D) confocal optical section. (A) 0-day culture. DiI labelling was performed at the region of the successional Lamina (arrowhead). (B) 2-day culture. (C) 7-day culture. (B,C) The label remains in the region of the successional Lamina (arrowhead) and in the forming second tooth (green asterisk). (D) Day 10. Magnification in D shows the framed area. Label is present in the second (green asterisk) and third (yellow asterisk) generation tooth germs and is retained in the successional Lamina (arrowhead) and adjacent mesenchyme (white asterisk). (E–F) Pantherophis guttatus Lef1 mRNA is located in the successional Lamina region (arrowhead), as observed by whole mount (E) and section (F) in situ hybridization. (G,G′,H) Sox2+ cells are found in the oral (asterisk) and aboral Dental Lamina (white arrows) and outer enamel epithelium (grey arrows), but are excluded from the successional Lamina (yellow arrowhead in G′, H). (G′) magnification of the region indicated in G. (H) Lingual plane showing the connection of the Dental Lamina with the oral epithelium. Scale bars: 100 µm.
Joy M Richman - One of the best experts on this subject based on the ideXlab platform.
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sox2 marks epithelial competence to generate teeth in mammals and reptiles
Development, 2013Co-Authors: Emma Juuri, Kerstin Seidel, Katrin Arnold, Maria Jussila, Scott Holmes, Joy M Richman, Kristiina Heikinheimo, Chengming Chuong, Konrad HochedlingerAbstract:Tooth renewal is initiated from epithelium associated with existing teeth. The development of new teeth requires Dental epithelial cells that have competence for tooth formation, but specific marker genes for these cells have not been identified. Here, we analyzed expression patterns of the transcription factor Sox2 in two different modes of successional tooth formation: tooth replacement and serial addition of primary teeth. We observed specific Sox2 expression in the Dental Lamina that gives rise to successional teeth in mammals with one round of tooth replacement as well as in reptiles with continuous tooth replacement. Sox2 was also expressed in the Dental Lamina during serial addition of mammalian molars, and genetic lineage tracing indicated that Sox2+ cells of the first molar give rise to the epithelial cell lineages of the second and third molars. Moreover, conditional deletion of Sox2 resulted in hyperplastic epithelium in the forming posterior molars. Our results indicate that the Sox2+ Dental epithelium has competence for successional tooth formation and that Sox2 regulates the progenitor state of Dental epithelial cells. The findings imply that the function of Sox2 has been conserved during evolution and that tooth replacement and serial addition of primary teeth represent variations of the same developmental process. The expression patterns of Sox2 support the hypothesis that dormant capacity for continuous tooth renewal exists in mammals.
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reptilian tooth development
Genesis, 2011Co-Authors: Joy M Richman, Gregory R HandriganAbstract:Dental patterns in vertebrates range from absence of teeth to multiple sets of teeth that are replaced throughout life. Despite this great variation, most of our understanding of tooth development is derived from studies on just a few model organisms. Here we introduce the reptile as an excellent model in which to study the molecular basis for early Dental specification and, most importantly, for tooth replacement. We review recent snake studies that highlight the conserved role of Shh in marking the position of the odontogenic band. The distinctive molecular patterning of the Dental Lamina in the labial-lingual and oral-aboral axes is reviewed. We explain how these early signals help to specify the tooth-forming and non-tooth forming sides of the Dental Lamina as well as the presumptive successional Lamina. Next, the simple architecture of the reptilian enamel organ is contrasted with the more complex, mammalian tooth bud and we discuss whether or not there is an enamel knot in reptilian teeth. The role of the successional Lamina during tooth replacement in squamate reptiles is reviewed and we speculate on the possible formation of a vestigial, post-permanent dentition in mammals. In support of these ideas, we present data on agamid teeth in which development of a third generation is arrested. We suggest that in diphyodont mammals, similar mechanisms may be involved in reducing tooth replacement capacity. Finally, we review the location of label-retaining cells and suggest ways in which these putative Dental epithelial stem cells contribute to continuous tooth replacement. genesis 49:247–260, 2011. © 2011 Wiley-Liss, Inc.
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identification of putative Dental epithelial stem cells in a lizard with life long tooth replacement
Development, 2010Co-Authors: Gregory R Handrigan, Kelvin Jiamien Leung, Joy M RichmanAbstract:Most dentate vertebrates, including humans, replace their teeth and yet the process is poorly understood. Here, we investigate whether Dental epithelial stem cells exist in a polyphyodont species, the leopard gecko (Eublepharis macularius). Since the gecko Dental epithelium lacks a histologically distinct site for stem cells analogous to the mammalian hair follicle bulge, we performed a pulse-chase experiment on juvenile geckos to identify label-retaining cells (LRCs). We detected LRCs exclusively on the lingual side of the Dental Lamina, which exhibits low proliferation rates and is not involved in tooth morphogenesis. Lingual LRCs were organized into pockets of high density close to the successional Lamina. A subset of the LRCs expresses Lgr5 and other genes that are markers of adult stem cells in mammals. Also similar to mammalian stem cells, the LRCs appear to proliferate in response to gain of function of the canonical Wnt pathway. We suggest that the LRCs in the lingual Dental Lamina represent a population of stem cells, the immediate descendents of which form the successional Lamina and, ultimately, the replacement teeth in the gecko. Furthermore, their location on the non-tooth-forming side of the Dental Lamina implies that Dental stem cells are sequestered from signals that might otherwise induce them to differentiate.