The Role of WNT/β-Catenin Signaling in Tongue Development and Homeostasis

Objectives: Craniofacial muscle development is distinctly different from axial skeletal muscle development. The WNT/β-catenin pathway is a highly evolutionary conserved pathway important in many developmental and morphogenic processes. Gene mutations in the WNT/β-catenin pathway cause muscular disorders and diseases in humans and mice. However, it is still largely unknown about the temporospatial role of WNT/β-catenin signaling in tongue development.
The aim of this study is to determine the role(s) of WNT/β-catenin signaling in tongue muscle cells during development and homeostasis. Particularly, we investigated how WNT/β-catenin signaling regulates each stage of development (cell proliferation, differentiation, and maintenance) using primary cells and tissue explants from the tongue. In addition, we investigated the function of WNT/β-catenin signaling in mice with ablation of β-catenin.
Methods: Tongue cells and tissues were treated with a WNT/β-catenin signaling inhibitor, endo-IWR1, at specific time-points of development and homeostasis. Mice with skeletal muscle-specific deletion of β-catenin (Myo-Cre;Ctnnb1^F/F mice) were used for histological analyses.
Results: An inhibition of WNT/β-catenin signaling decreased proliferation activity, but did not induce cell death, through the regulation of genes Ccna2 and Cdc25c. During muscle differentiation, the inhibition of WNT/β-catenin signaling blocked myoblast fusion through downregulated expression of the Fermt2 gene. In well-differentiated myofibers, the blockade of WNT/β-catenin signaling induced disruption of cadherin/β-catenin/actin complex formation and resulted in a failure of maintenance of their muscular structure. Corresponding to our in vitro findings, Myo-Cre;Ctnnb1^F/F mice exhibited a significant decrease in tongue size and disorganized muscle fiber formation, compared to littermate controls.
Conclusions: Our results indicate that WNT/β-catenin signaling can regulate multiple steps of myogenesis by targeting step-specific molecules. Our study sheds light on muscular disorders related to the WNT/β-catenin signaling and will help develop procedures for keeping homeostasis and accelerating regeneration of tongue muscles.