Down-regulation of Msx1 antisens RNA expression by 1,25α(OH)₂VitaminD3 in ameloblasts

Clinical investigations report the existence of enamel and dentin alterations in vitamin D-related pathologies. Tooth morphogenesis results from the combinatorial action of different homeobox genes expressed in the facial neural-crest-derived mesenchyme. One of them, Msx1, is involved in cell proliferation and inhibits cell differentiation. A sense and a cis-antisens (AS) RNA are transcribed from Msx1 gene. They are present during tooth morphogenesis, but AS fonction is not clearly identified. It can modulate the distribution of the protein. Most of target organs of Msx1 are also known for their sensitivity to 1,25a(OH)₂VitaminD3 (vitD).

Objective: To elucidate the influence of vitD on the Msx1 sense and AS RNA expression pattern during dental cell differentiation. Methods: Msx1 sense and AS transcripsts was detected by in situ hybridization in postnatal mouse mandibular incisors. 21 day-old CD1 mice were carenced in vitamin D-free conditions during 5 weeks. Some of them were repleated with vitD injection. RNA from the microdissected dental epithelium and mesenchyme of incisors, and from amelobast-like cells (LS8) treated by VitD were analyzed by RT-PCR. Results: Sense was detected in preodontoblast cells, odontoblasts, pulp and dental follicle cells. Antisense was detected in ameloblasts, odontoblasts and dental follicle cells. This incisor pattern is different from the previously established for molar, and it overlaps the VDR expression. In incisor of vitamin D-deficient mice, a increase in Msx1 AS RNA expression in epithelium was showed without both the alteration of sense expression, and the modification of Msx1 transcript expressions in mesenchyme. The up-regulation of Msx1 expression in epthelium was rescued in incisor of vitamin D-repleated mice. In vitro, vitD treated LS8 cells confirmed the down-regulation of Msx1 AS RNA expression by vitD. Conclusion: Altogether, our results suggest that Msx1 is an actor in the dental phenotype of vitD-related pathologies.