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International audience; Reciprocal epithelial-mesenchymal interactions control odontogenesis and the cap stage tooth germ mesenchyme specifies crown morphogenesis. The aim of this work was to determine whether this mesenchyme could also control epithelial histogenesis. Dental mesenchyme and enamel organ were dissociated from mouse first lower molars at E14. At this early cap stage, the enamel organ consists of four cell types forming the inner dental epithelium (IDE), primary enamel knot (PEK), outer dental epithelium (ODE) and the stellate reticulum (SR). Pelleted trypsin-dissociated single dental epithelial cells, which had lost all positional information, were reassociated to either dental mesenchyme or dissociated mesenchymal cells and cultured in vitro. Although with different timings, teeth developed in both types of experiments showing a characteristic dental epithelial histogenesis, cusp formation, and the differentiation of functional odontoblasts and ameloblasts. The rapid progression of the initial steps of histogenesis suggested that the cell history was not memorized. The dental mesenchyme, as well as dissociated mesenchymal cells, induced the formation of a PEK indicating that no specific organisation in the mesenchyme is required for this step. However, the proportion of well-formed multicusped teeth was much higher when intact mesenchyme was used instead of dissociated mesenchymal cells. The mesenchymal cell dissociation had consequences for the functionality of the newly-formed PEK.

International audience; Recent developments in tooth-tissue engineering require that we understand the regulatory processes to be preserved to achieve histomorphogenesis and cell differentiation, especially for enamel tissue engineering. Using mouse first lower molars, our objectives were: (1) to determine whether the cap-stage dental mesenchyme can control dental epithelial histogenesis, (2) to test the role of the primary enamel knot (PEK) in specifying the potentialities of the dental mesenchyme, and (3) to evaluate the importance of positional information in epithelial cells. After tissue dissociation, the dental epithelium was further dissociated into individual cells, re-associated with dental mesenchyme, and cultured. Epithelial cells showed a high plasticity: Despite a complete loss of positional information, they rapidly underwent typical dental epithelial histogenesis. This was stimulated by the mesenchyme. Experiments performed at E13 demonstrated that the initial potentialities of the mesenchyme are not specified by the PEK. Positional information of dental epithelial cells does not require the memorization of their history.