Characterization of Scheduled Tooth Resorption in the Leopard Gecko

Objectives: The leopard gecko (Eublepharis macularius) like most lizards and snakes, replaces its teeth throughout life. Unlike mammals, geckos form a direct bone-tooth attachment that must be resorbed each time a tooth is lost. The gecko offers a unique opportunity to study tooth resorption in a normal rather than a pathological condition. As a first step, we stained putative odontoclasts using Tartrate Acid Resistance Phosphatase (TRAP). In addition, we performed radioactive in-situ hybridization with a probe that recognizes nuclear factor kappa beta subunit 1 (NFKB1). NFKB1 is downstream of The Receptor Activator of Nuclear Factor-Κβ Ligand (RANKL) which binds to RANK receptor, mediating osteoclast formation.
Methods: We performed TRAP staining in sections of two adult animals, and we quantified the area that TRAP+ cells occupied in the dental pulp of thirteen mature teeth. We also performed in-situ hybridization against NFKB1 on adjacent tissue sections from the same animals.
Results: The area of TRAP+ cells in relation to the area of the pulp cavity varied radically between adjacent teeth. There were teeth with high levels of TRAP staining (56% of the pulp area) interspersed between teeth with very few stained cells (0.4%). In situ hybridization revealed a correlation between high levels of TRAP staining and strong NFKB1 in the most mature teeth, close to exfoliation. The teeth with few TRAP cells had relatively low expression of NFKB1 RNA. The source of the RNA appears to be cells close to the odontoblast layer.
Conclusions: The resorption of the tooth attachment in gecko teeth bears a resemblance to the creation of an eruption pathway in mammals. Our studies suggest that the RANKL/RANK pathway is involved, possibly increasing expression in advance of the invasion of odontoclasts.