Earliest migratory cephalic NC cells are potent to differentiate into dental ectomesenchyme of the two lungfish dentitions: tetrapodomorph ancestral condition of unconstrained capability of mesencephalic NC cells to form oral teeth

Abstract

Reciprocal interactions between epithelial and neural crest-derived mesenchymal cells have been recognized in the evolutionary modulation of tetrapod odontodes, skeletal structures that include the teeth and tooth-integrated basal tissue. Using cell-tracking experiments, it has been demonstrated that mandibular neural crest cells, labelled during migration, extensively populate dental papillae of all tooth phenotypes of the lobe-finned fish, the Australian lungfish (Neoceratodus forsteri). Here, I report on an extension of this experimental study that earliest migrating NC cells are able to differentiate into odontogenic ectomesenchyme. Using vital dye cell-tracking to mark the mesencephalic neural crest prior to migration, I have found that the corresponding population of earliest migratory cells selectively relocated to dental papillae of both temporary and permanent dentitions of Neoceratodus. I noticed a gradient in distribution of the labelled cells which populated posterior teeth, pterygoid and prearticular (including associated trabecular and Meckelian cartilages; major relocation) much more densely than those in anterior marginal positions, temporary and vomeral permanent teeth (minor relocation). Contrary to mice and zebrafish, the odontogenic potency of mesencephalic neural crest cells is already programmed at the onset of the migration event in lungfish. This may imply that the morphogenic potential of mesencephalic neural crest cells to form teeth has been heterochronically shifted and constrained to later migratory populations of neural crest cells during the developmental evolution of derived tetrapods, or/and arrested in their expression in the oral development of some modern osteichthyans.