Role of RANKL (TNFSF11)-Dependent Osteopetrosis in the Dental Phenotype of Msx2 Null Mutant Mice

Beatriz Castaneda,Benoit Robert,Ariane Berdal,Yohann Simon,Christopher Mueller,Didier Ferbus,Julie Chesneau,Frédéric Lézot,Laurent Viriot

doi:10.1371/journal.pone.0080054

Abstract

The MSX2 homeoprotein is implicated in all aspects of craniofacial skeletal development. During postnatal growth, MSX2 is expressed in all cells involved in mineralized tissue formation and plays a role in their differentiation and function. Msx2 null (Msx2 −/−) mice display complex craniofacial skeleton abnormalities with bone and tooth defects. A moderate form osteopetrotic phenotype is observed, along with decreased expression of RANKL (TNFSF11), the main osteoclast-differentiating factor. In order to elucidate the role of such an osteopetrosis in the Msx2 −/− mouse dental phenotype, a bone resorption rescue was performed by mating Msx2 −/− mice with a transgenic mouse line overexpressing Rank (Tnfrsf11a). Msx2 −/− RankTg mice had significant improvement in the molar phenotype, while incisor epithelium defects were exacerbated in the enamel area, with formation of massive osteolytic tumors. Although compensation for RANKL loss of function could have potential as a therapy for osteopetrosis, but in Msx2 −/− mice, this approach via RANK overexpression in monocyte-derived lineages, amplified latent epithelial tumor development in the peculiar continuously growing incisor.

Highlights

Mutations in muscle segment homeobox (MSX) transcription factors cause craniofacial malformations such as cleft palate for MSX1 and craniosynostosis (Boston type) for MSX2 [1]
In order to investigate the importance of osteopetrosis in Msx22/2 mouse dental defects, we developed a strategy to rescue bone resorption by overexpressing RANK in osteoclast precursors [8] of Msx22/2 mice
Males that were heterozygous for the Msx2 gene mutation and overexpressed Rank were mated with females heterozygous for the Msx2 gene mutation in order to generate all possible Msx2 and Rank genotypes

Summary

Introduction

Mutations in muscle segment homeobox (MSX) transcription factors cause craniofacial malformations such as cleft palate for MSX1 and craniosynostosis (Boston type) for MSX2 [1]. An MSX2 mutation is associated with amelogenesis imperfecta [2], highlighting the importance of this protein in dental epithelial cell differentiation and function. The fact that MSX2 is required for normal dental epithelial cell fates is supported by the Msx22/2 mouse dental phenotype. These mutant mice present amelogenesis imperfecta and root dysmorphia associated with differentiation defects in epithelial cells (i.e., ameloblastic tumors and defects in Hertwig epithelial root sheaths [HERS] and epithelial cell rests of Malassez) [3,4,5]. Gene expression of the key osteoclast differentiation factor RANKL is severely decreased in the dental epithelium and alveolar bone of Msx22/2 mice [3,4,5]. The phenotypes of different teeth were analyzed in these mice

Methods

Results

Conclusion