Dlx5 Plays a Critical Role During Soft Palate Muscle Development

Objectives: The oropharyngeal region that includes the soft palate plays an important role in our daily activities such as speech, swallowing, breathing and hearing. To explore an optimal approach to soft palate muscle restoration, we need to expand our understanding of the molecular regulatory and cellular mechanisms of soft palate development. Our previous study demonstrated that Dlx5 controls oronasal patterning in the anterior part of the palatal shelf. However, where Dlx5 is expressed in the posterior part of the palate and whether Dlx5 plays an important role in regulating the development of the soft palate has remained unknown. In this study, we examined the role of Dlx5 during soft palate muscle development.
Methods: MicroCT scanning and histological analysis were performed to analyze the phenotypes of Dlx5^-/- and control mice. We also generated Wnt1-Cre;ZsGreen and Dlx5-Cre;tdTomato mice for expression pattern analysis. The cells were isolated from Dlx5^-/- and control mice and were cultured for analyzing the downstream targets of Dlx5 signaling.
Results: Dlx5^-/- mice exhibited a shortened palate, ending in a posterior uvula-like structure. In the soft palate, loss of Dlx5 resulted in the defects of the levator veli palatini (LVP), palatopharyngeus (PLP), and palatoglossus muscles, but the tensor veli palatini was unaffected. Dlx5-positive cranial neural crest (CNC) cells were adjacent to muscle progenitor cells in the LVP and PLP regions. In addition, loss of Dlx5 led to an increase in apoptosis and decrease in proliferation in the LVP and PLP regions. In Dlx5^-/- mice, expression of Fgf10 was downregulated in the LVP and PLP regions. Finally, treatment of Dlx5^-/- cells with FGF10 rescued differentiation of muscle progenitor cells and proliferative ability of CNC cells.
Conclusions: Dlx5-FGF10 signaling cascade plays an important role during muscle development of the LVP and PLP likely via interactions between CNC-derived and muscle progenitor cells.