Egg Tooth Morphogenesis in the Leopard Gecko: A Model for Dental Size Variation
Notice bibliographique
Résumé
Tooth size can vary along a tooth row in an individual organism, and can also change through time as new teeth replace erupted ones. Although much is known about morphoregulation of the dentition in mammals, little is known about what controls tooth size and shape in other heterodont amniotes. In this study, we examine tooth development through growth in the leopard gecko Eublepharis macularis in order to understand the timing of tooth mineralization and its contribution to sizing differences in teeth. The embryonic leopard gecko has greatly enlarged, anteriorly oriented egg teeth that are shed a few days after hatching, and show a dramatic phenotype for studying size variation in an organ. Typical tooth replacement in polyphyodont animals involves the replacement of a small tooth with a larger tooth through growth, whereas in the hatchling leopard gecko several smaller teeth replace the very large egg tooth. In this study, we aimed to: 1) quantify differences in tooth size at the very earliest stages of tooth development; and 2) visualize the mineralization pattern in egg and marginal teeth in ovo. An understanding of the timing and process of tooth mineralization in the leopard gecko will serve as a framework to address larger questions of development and the control of shape and size of teeth, especially when considering variation in heterodont dentitions in polyphyodont animals. To document the development of the egg tooth and marginal teeth, 13 specimens were fixed at different developmental stages: 6 weeks before hatching to hatching, before the egg teeth were shed. Specimens were examined histologically with and without decalcification, and cells in developing tooth buds were counted as a proxy for the size of the tooth germ. In separate experiments, embryos were injected with two fluorescent dyes, calcein and xylenol orange, 5 days apart in ovo to mark teeth that were actively mineralizing. The entire tooth row was examined with Optical Projection Tomography (OPT) to view the fluorescent mineralization fronts in 3D. Subsequently, specimens were stained with phosphotungstic acid to enhance contrast and micro CT scanned to observe the morphology of the dental lamina and egg teeth at hatching. Results show that at stage 33 (~14 days post oviposition) the egg tooth is at the cap stage, whereas the rest of the functional teeth are at bud stage or earlier. The dental placode for the egg tooth has a higher cell count than those of the marginal teeth. The fluorescent mineralization fronts indicate that the egg tooth remains in the histogenesis phase for a longer period of time than the marginal teeth, and that mineralization is asymmetrical in the last stages of embryonic growth to create the forward curvature of the tooth. The increased size of the egg tooth is due in part to early initiation and a greater number of cells allocated to the dental placode. Further experiments will determine whether other mechanisms such as increased proliferation and accelerated differentiation are involved in regulating tooth organ size. Support or Funding Information Michael Smith Foundation for Health Research, Killam Postdoctoral Fellowship, National Institutes of Health, National Sciences and Engineering Research Council of Canada
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Comment cette classification a été obtenuedéplier
Prédiction machine sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Le volet Gemma est une étiquette directe du modèle pour chaque travail de la base, lue sur la notice réduite au titre. Le volet Codex est un classifieur appris des 10 348 étiquettes directes de Codex et calibré sur les taux pondérés de l'échantillon; les champs sans appui suffisant ne portent aucun appel Codex. Le mode candidate est l'union des deux volets; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont pas des étiquettes humaines.
Scores du classifieur distillé par catégorie (deux têtes)
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,000 | 0,000 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,000 | 0,000 |
| Études des sciences et des technologies | 0,000 | 0,001 |
| Communication savante | 0,000 | 0,000 |
| Science ouverte | 0,000 | 0,000 |
| Intégrité de la recherche | 0,000 | 0,000 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,001 | 0,000 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découleClassification
machine, non validéePrédiction automatique; un appel candidat d’une seule source (Gemma direct ou Codex distillé), pas un consensus.
Le détail, modèle par modèle et score par score, se trouve en fin de page sous « Comment cette classification a été obtenue ».