The Vertebrate Tooth Row: Is It Initiated by a Single Organizing Tooth?

Abstract

Teeth are one of the most fascinating innovations of vertebrates. Their diversity of shape, size, location, and number in vertebrates is astonishing. If the molecular mechanisms underlying the morphogenesis of individual teeth are now relatively well understood, thanks to the detailed experimental work that has been performed in model organisms (mainly mouse and zebrafish), the mechanisms that control the organization of the dentition are still a mystery. Mammals display simplified dentitions when compared to other vertebrates with only a single tooth row positioned in the anterior part of the mouth, whereas other vertebrates exhibit tooth rows in many locations. As proposed 60 years ago, tooth rows can be formed sequentially from an initiator tooth. Recent results in zebrafish have now largely confirmed this hypothesis. Here this observation is generalized upon and it is suggested that in most vertebrates tooth rows could form sequentially from a single initiator tooth.

Oral and Palatal Dentition of Axolotl Arises From a Common Tooth-Competent Zone Along the Ecto-Endodermal Boundary

“…In the mouse, the first tooth germ similarly initiates the whole molar row ( Prochazka et al, 2010 ; Sadier et al, 2019 ). The first tooth thus acts as an initiator cue for the development of the whole tooth row or tooth patch ( Sadier et al, 2020 ) while spacing between the teeth is mediated by the zone of inhibition surrounding each tooth germ ( Osborn, 1978 ; Huysseune and Witten, 2006 ; Fraser et al, 2008 ). In the axolotl, the position of the initiator-tooth is specific to each tooth field ( Figure 7 ) and these different positions next trigger disparate ways, in which new germs are added (see Huysseune and Witten, 2006 ).…”

“…Absence of Shh or Pitx2 signaling results in the loss of tooth signaling centers, defects in tooth development, and missing teeth ( Lin et al, 1999 ; Dassule et al, 2000 ; Cobourne et al, 2004 ; Jackman et al, 2010 ; Yu et al, 2020 ), and a lack of co-expression of Shh and Pitx2 , for example, is associated with toothlessness in cypriniforms ( Jackman et al, 2010 ). Once Shh and Pitx2 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 initiator-tooth ( 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 then leads to the final appearance of the respective tooth field.…”

Tissue-Nonspecific Alkaline Phosphatase—A Gatekeeper of Physiological Conditions in Health and a Modulator of Biological Environments in Disease

“…Teeth are usually formed by the orthodentine that is located close to the pulp cavity and are covered with an enameloid cap [115]. Zebrafish are constantly replacing their teeth, and the starter tooth (named 4V1) is stimulating and probably initiating the development of the following ones in the pharynx [116]. Adult Zebrafish dentition includes three rows with five ventral teeth, four mediodorsal teeth, and two dorsal teeth on each side [117].…”

Novel Insights into Tooth Row Development: From Old Ideas to New Concepts

“…The recent paper by Sadier, Jackman, Laudet, and Gibert is important because it proposes a generalized model in which tooth rows develop sequentially from a single first‐formed tooth starting the inhibitor cascade for subsequent tooth development. [ 3 ]…”

“…Changes in activation/inhibition signals during jaw development are assumed to result in variations of tooth development between species and clades. [ 3 ]…”