The Molecular Circuit Regulating Tooth Development in Crocodilians

Abstract

Alligators have robust regenerative potential for tooth renewal. In contrast, extant mammals can either renew their teeth once (diphyodont dentition, as found in humans) or not at all (monophyodont dentition, present in mice). Previously, the authors used multiple mitotic labeling to map putative stem cells in alligator dental laminae, which contain quiescent odontogenic progenitors. The authors demonstrated that alligator tooth cycle initiation is related to β-catenin/Wnt pathway activity in the dental lamina bulge. However, the molecular circuitry underlying the developmental progression of polyphyodont teeth remains elusive. Here, the authors used transcriptomic analyses to examine the additional molecular pathways related to the process of alligator tooth development. The authors collected juvenile alligator dental laminae at different developmental stages and performed RNA-seq. This data shows that Wnt, bone morphogenetic protein (BMP), and fibroblast growth factor (FGF) pathways are activated at the transition from pre-initiation stage (bud) to initiation stage (cap). Intriguingly, the activation of Wnt ligands, receptors and co-activators accompanies the inactivation of Wnt antagonists. In addition, the authors identified the molecular circuitry at different stages of tooth development. The authors conclude that multiple pathways are associated with specific stages of tooth development in the alligator. This data shows that Wnt pathway activation may play the most important role in the initiation of tooth development. This result may offer insight into ways to modulate the genetic controls involved in mammalian tooth renewal.

Use of Thrombocyte–Leukocyte-Rich Plasma in the Treatment of Chronic Oral Cavity Disorders in Reptiles: Two Case Reports

“…Although scientific literature refers mostly to mammal species, recent publications confirm that these molecules play similar roles in reptile wound healing. Evidence derives from studies regarding growth factors under physiological conditions such as IGF-1 being widely expressed in reptile blood and tissues, [37][38][39][40] FGF playing a major role in crocodile teeth replacement, 41 crocodile oil containing TGF-b at concentrations proven to enhance wound healing and reduce scar formation. 42 Under pathological conditions, tissue IL-6 increases during inflammation in turtles, 43 PDGF is highly expressed in lizards spinal cord after tail amputation, 44 and VGEF contributes to gecko's wound healing and tail regrowth.…”

Dental replacement in Mesozoic birds: evidence from newly discovered Brazilian enantiornithines

“…While teeth are replaced on a schedule that is independent of wear or damage 7 , the underlying regulatory mechanism of the replacement process has been difficult to understand. Within reptiles, modern studies of crocodilians—the only present-day toothed archosaurs—have demonstrated that the dental laminae within the alveoli (tooth sockets) form a niche of stem cells for the multiple generations of teeth, and that this mechanism is regulated by expression of a network of regulatory genes 8 , 9 . Even though our understanding of tooth development in extinct archosaurs, and its underlying regulatory mechanism, is still in its infancy, polyphyodonty has been documented for a range of extinct archosaurs 10 – 12 , including the toothed stem birds of the Mesozoic Era 13 – 15 .…”