Previous studies indicated that the elevated mesenchymal Wnt/β-catenin signaling deprived dental mesenchyme of odontogenic fate. By utilizing ex vivo or pharmacological approaches, Wnt/β-catenin signaling in the developing dental mesenchyme was suggested to suppress the odontogenic fate by disrupting the balance between Axin2 and Runx2. In our study, the Osr2-cre KI ; Ctnnb1 ex3f mouse was used to explore how mesenchymal Wnt/β-catenin signaling suppressed the odontogenic fate in vivo. We found that all of the incisor and half of the molar germs of Osr2-cre KI ; Ctnnb1 ex3f mice started to regress at E14.5 and almost disappeared at birth. The expression of Fgf3 and Msx1 was dramatically down-regulated in the E14.5 Osr2-cre KI ; Ctnnb1 ex3f incisor and molar mesenchyme, while Runx2transcription was only diminished in incisor mesenchyme. Intriguingly, in the E14.5 Osr2-cre KI ; Ctnnb1 ex3f incisor epithelium, the expression of Noggin was activated, while Shh was abrogated. Similarly, the Wnt and BMP antagonists, Ectodin and Noggin were also ectopically activated in the E14.5 Osr2-cre KI ; Ctnnb1 ex3f molar epithelium. Recombination of E13.5 Osr2-cre KI ; Ctnnb1 ex3f molar mesenchyme with E10.5 and E13.5 WT dental epithelia failed to develop tooth. Taken together, the mesenchymal Wnt/β-catenin signaling resulted in the loss of odontogenic fate in vivo not only by directly suppressing odontogenic genes expression but also by inducing Wnt and BMP antagonists in dental epithelium.

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Family with sequence similarity 20, member A (Fam20a) encodes a pseudokinase which is regarded to facilitate the role of Fam20c in phosphorylating secreted proteins. Fam20c deficiency causes Raine Syndrome in human and impaired the amelogeneis, dentiogenesis and osteogenesis in mice. Mutations in Fam20a are associated with Amelogenesis Imperfecta and Enamel-Renal Syndrome in human. Similarly, abrogation of Fam20a in ectoderm caused Amelogeneis Imperefeca in mice, however, the global knock-out of Fam20a in mice showed few anomaly in dentin and bone. In this study, the Fam20a LacZ mice showed that at the E17.5, the LacZ staining was located in the osteogenic lining of calvarium and mandibular bone, odontoblasts, ameloblasts, the gingival and subcutaneous fibroblasts. During the postnatal life, the LacZ staining was detected in the osteogenic and gingival cells in mandibular bone, as well as the osteogenic and the marrow cells in long bone, but excluded from the joint cartilage. Both the LacZ staining in the mandibular and long bone became faint with the life increased. To address if Fam20a is required for the role of Fam20c during the dentinogenesis and osteogenesis, we first examined the mandibular bone and femur of the Wnt1-cre;Fam20a f/f , Osr2-cre;Fam20a f/f and Col1-cre; Fam20a f/f mice. The gross views and X-ray plain images showed no difference in the tissue morphology and mineralization density between these conditional knock-out mice and their controls. Our findings suggested that Fam20a was not required by Fam20c during dentinogenesis and osteogenesis.