Runx2 Regulates Mouse Tooth Root Development Via Activation of WNT Inhibitor NOTUM

Progenitor cells are crucial in controlling organ morphogenesis. Tooth development is a well-established model for investigating the molecular and cellular mechanisms that regulate organogenesis. Despite advances in our understanding of how tooth crown formation is regulated, we have limited understanding of tooth root development. Runt-related transcription factor 2 (RUNX2) is a well-known transcription factor in osteogenic differentiation and early tooth development. However, the function of RUNX2 during tooth root formation remains unknown. We revealed in this study that RUNX2 is expressed in a subpopulation of GLI1+ root progenitor cells, and that loss ofRunx2in these GLI1+ progenitor cells and their progeny results in root developmental defects. Our results provide in vivo evidence thatRunx2plays a crucial role in tooth root development and in regulating the differentiation of root progenitor cells. Furthermore, we identified thatGli1,Pcp4,NOTUM, and Sfrp2 are downstream targets ofRunx2by integrating bulk and single-cell RNA sequencing analyses. Specifically, ablation ofRunx2results in downregulation of WNT inhibitorNOTUMand upregulation of canonical WNT signaling in the odontoblastic site, which disturbs normal odontoblastic differentiation. Significantly, exogenous NOTUM partially rescues the impaired root development in Runx2 mutant molars. Collectively, our studies elucidate howRunx2achieves functional specificity in regulating the development of diverse organs and yields new insights into the network that regulates tooth root development. (c) 2020 The Authors.Journal of Bone and Mineral Researchpublished by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).