Abstract
Vertebrate dentitions arise at various places within the oropharyngeal cavity including the jaws, the palate, or the pharynx. These dentitions develop in a highly organized way, where new tooth germs are progressively added adjacent to the initiator center, the first tooth. At the same time, the places where dentitions develop house the contact zones between the outer ectoderm and the inner endoderm, and this colocalization has instigated various suggestions on the roles of germ layers for tooth initiation and development. Here, we study development of the axolotl dentition, which is a complex of five pairs of tooth fields arranged into the typically tetrapod outer and inner dental arcades. By tracking the expression patterns of odontogenic genes, we reason that teeth of both dental arcades originate from common tooth-competent zones, one present on the mouth roof and one on the mouth floor. Progressive compartmentalization of these zones and a simultaneous addition of new tooth germs distinct for each prospective tooth field subsequently control the final shape and composition of the axolotl dentition. Interestingly, by following the fate of the GFP-labeled oral ectoderm, we further show that, in three out of five tooth field pairs, the first tooth develops right at the ecto-endodermal boundary. Our results thus indicate that a single tooth-competent zone gives rise to both dental arcades of a complex tetrapod dentition. Further, we propose that the ecto-endodermal boundary running through this zone should be accounted for as a potential source of instruction factors instigating the onset of the odontogenic program.
Highlights
One of the most important features of vertebrate dentitions is the patterned arrangement of their elemental units, the teeth
In order to understand how this dentition acquires such a complex arrangement, we studied the expression of the early odontogenic markers Pitx2 and Shh
Further analysis of expression patterns of other odontogenic factors, such as Bmp2, Bmp7, or Dlx5, confirms the addition of new tooth germs within individual tooth fields, which are delineated by the expression of Dlx3 (Supplementary Figure 1)
Summary
One of the most important features of vertebrate dentitions is the patterned arrangement of their elemental units, the teeth. Each tooth has its defined position and a particular relation to other teeth of that dentition. Tooth development is restricted to the oropharyngeal region, where the locally thickened epithelium demarcates the prospective tooth-forming areas. This socalled odontogenic band usually invaginates into the underlying mesenchyme where it forms an epithelial strand, the dental lamina. Once Shh and Pitx specify the positions of the nascent dentition, a sequence of events leading to the appearance of the first tooth controls the addition of further tooth germs adjacent to this initiatortooth (Gibert et al, 2019; Sadier et al, 2019, 2020). The way in which new tooth germs are sequentially added in the vicinity of this initiator-tooth leads to the final appearance of the respective tooth field
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