Notum Regulates the Cusp and Root Patterns in Mouse Molar

Notumis a direct target of Wnt/β-catenin signaling and plays a crucial role as a Wnt inhibitor within a negative feedback loop. In the tooth, Notum is known to be expressed in odontoblasts, and severe dentin defects and irregular tooth roots have been reported in Notum-deficient mice. However, the precise expression pattern of Notum in early tooth development, and the role of Notum in crown and root patterns remain elusive. In the present study, we identified a novel Notum expression in primary enamel knot (EK), secondary EKs, and dental papilla during tooth development. Notum-deficient mice exhibited enlarged secondary EKs, resulting in broader cusp tips, altered cusp patterns, and reduced concavity in crown outline. These alterations in crown outline led to a reduction in cervical tongue length, thereby inducing root fusion in Notum-deficient mice. Overall, these results suggest that the size of secondary EK size, regulated by the Wnt/Notum negative feedback loop, has a significant impact on the patterns of crown and root during tooth morphogenesis. To investigate the gene expression pattern and the role of Notum in the developing tooth, Notum knockout mouse (Notumem1(IMPC)Tcp) generated on the C57BL/6N background strain were purchased from the international mouse phenotyping consortium (IMPC) and mated with C57BL/6N wild-type mice to get the future generations. All animal experiments were performed under approved protocols of the Intramural Animal Use and Care Committee of the Yonsei University College of Dentistry. Notum-/- mice and the Notum+/+ control mice embryonic day (E) 14.5 and E16.5 maxillary and mandibular molar tooth germs RNA were isolated, and bulk RNA sequencing was performed. Comparative gene expression profiling analysis of the RNA-seq data for Notum-/- mice and the Notum+/+ was performed at E14.5 and E16.5.