Response to Letter to the Editor, “Osterix Regulates Tooth Root Formation in a Site-specific Manner”

Abstract

Feng et al. 2015) in response to our article titled "Osterix Regulates Tooth Root Formation in a Site-specific Manner" (Kim et al. 2015).A major issue is raised from our interpretation about the localization of Osterix and dentin phenotypes of 2 independent conditional Osterix knockout mouse lines (Kim et al. 2015). Dr. Feng's group recently reported that Osterix has an essential role in tooth root but not crown dentin formation (Zhang et al. 2015). Regardless of the difference in transactivators, dentin phenotype seems to be similar in Osterix mutants of 2 reports.In our observation, Osterix mutant mice did not show remarkable dentin phenotype in crown but did exhibit severe impairment of interradicular dentin in molar roots. In this region, both dental mesenchyme and HERS proliferation was relatively lower than in the root elongation region. This finding indicates that Osterix plays a critical role in odontoblast differentiation in a site-specific manner. In this context, it is notable that "rootless" teeth are produced without crown defect in the tissue-specific β-catenin inactivation mice (Kim et al. 2013).We also examined tooth phenotype of Osterix null newborn mice (Appendix Fig.). Although crown morphogenesis was normal, differentiation of both odontoblasts and ameloblasts was disrupted as reported previously (Clarke et al. 2014). In addition, Osterix is known to be short-lived protein, easily sumoylated and ubiquitinated (Hosoya et al. 2013;Peng et al. 2013). It could be associated with the discrepancies in Osterix expression between mRNA and protein level.We hope that our finding could contribute to further understanding the principles underlying tooth root formation.