How the evolution of tooth enamel tissue unfolded

evolution of tooth enamel tissue
Photo: olegdudko 123rf

Studies of mammalian evolution often rely on the analyses of teeth, which are the best-preserved parts of fossilised skeletons. Tooth morphology and the composition of enamel—the most mineralised tissue of the body—constitute important criteria for speciation events that occurred over 200 million years of evolution. These evolutionary adaptations, which are linked to genetic modifications, have contributed to the extensive diversification of cell types in animals.

A team of researchers from the Center of Dental Medicine at the University of Zurich has identified the Notch pathway as the key gene network that is responsible for changes in tooth shape and enamel composition during evolution—publishing their findings in Cellular and Molecular Life Sciences

The Notch pathway is an ancient, evolutionary conserved signaling mechanism that controls cell-fate decisions and proper morphogenesis of most organs, including teeth.

Using genetically modified mouse models, the research team analysed the effects of the Notch-ligands in teeth. Absence of those ligand molecules affected tooth morphology and enamel formation due to the alteration of numerous significant morphogenetic genes. Deregulation of the Notch pathway reverted the evolutionary cascade, thus generating less complex dental structures that are more reminiscent of the enameloid of fishes rather than that of mammalian enamel.

“We hypothesise that the evolution of teeth depends on Notch signaling for the generation of new dental cell types from already existing primitive dental cell types, thus allowing the formation of more complex and unique dental structures such as tooth enamel,” first author Dr Thimios Mitsiadis said.

The correlation between Notch molecules and the generation and/or maintenance of distinct dental cell types could represent a general mechanism underlying the evolution of specialised cell types in mammals. 

“In teeth, deregulation of Notch signaling initiates the suppression of specific dental cell types that were acquired during evolution,” Dr Mitsiadis said. 

“Loss of these cells leads to the generation of enamel malformations and tooth morphological alterations.”

Modelling of these changes allows predictions of how Notch-associated mutations in humans could affect the morphology and enamel of their teeth.

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