Organized Emergence of Multiple-Generations of Teeth in Snakes Is Dysregulated by Activation of Wnt/Beta-Catenin Signalling

Marcia Gaete,Abigail S Tucker,Michael Schubert

doi:10.1371/journal.pone.0074484

Marcia Gaete, Abigail S Tucker + Show 1 more

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https://doi.org/10.1371/journal.pone.0074484

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Abstract

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.

Highlights

Polyphyodonty, the capacity for continuous tooth renewal, is displayed in most vertebrates, including amphibians, fish and reptiles
In order to illustrate the pattern of tooth replacement in the corn snake (Pantherophis guttatus), we examined the dentition in the newborn snake using skeletal staining, microCT scan and oral examination
To investigate the formation of several dental generations, we examined dental organs of snake embryos at different days-post-ovoposition to identify the stages of successional lamina development

Summary

Introduction

Polyphyodonty, the capacity for continuous tooth renewal, is displayed in most vertebrates, including amphibians, fish and reptiles. Teeth are derived from the oral epithelium and neural-crest derived mesenchyme [1,2,3] They develop through key morphological stages, dental lamina, bud, cap and bell, according to the shape that the epithelium adopts. In the monophyodont mouse only one generation of teeth are formed, while in polyphyodont reptiles new generations are continuously formed throughout life [1,3] and can be observed in a newborn snake (Figure 1A–C). Tooth development in polyphyodont reptiles is initiated by the formation of an epithelial dental lamina that grows into the developing jaw. The transcription factor SRY (sex determining region Y)-box 2 (Sox2) has being described as a marker of epithelial dental stem cells [5]

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