Our previous studies have demonstrated that Fam20 C promotes differentiation and mineralization of odontoblasts,ameloblasts,osteoblasts and osteocytes during tooth and bone development.Ablation of the Fam20 C gene inhibits bone and tooth growth by increasing fibroblast growth factor 23 in serum and causing hypophosphatemia in conditional knockout mice.However,control and regulation of the expression of Fam20 C are still unknown.In this study,we generated a transgenic reporter model which expresses green fluorescence protein(GFP) driven by the Fam20 C promoter.Recombineering was used to insert a 16 kb fragment of the mouse Fam20 C gene(containing the 15 kb promoter and 1.1 kb of exon 1) intoa pBluescript SK vector with the topaz variant of GFP and a bovine growth hormone polyadenylation sequence.GFP expression was subsequently evaluated by histomorphometry on cryosections from E14 to adult mice.Fluorescence was evident in the bone and teeth as early as E17.5.The GFP signal was maintained stably in odontoblasts and osteoblasts until 4 weeks after birth.The expression of GFP was significantly reduced in teeth,alveolar bone and muscle by 8 weeks of age.We also observed colocalization of the GFP signal with the Fam20 C antibody in postnatal 1- and 7-day-old animals.Successful generation of Fam20C-GFP transgenic mice will provide a unique model for studying Fam20 C gene expression and the biological function of this gene during odontogenesis and osteogenesis. Our previous studies have demonstrated that Fam20 C promotes differentiation and mineralization of odontoblasts, ameloblasts, osteoblasts and osteocytes during tooth and bone development. Ablation of the Fam20 C gene inhibits bone and tooth growth by increasing fibroblast growth factor 23 in serum and causing hypophosphatemia in conditional Knockout mice. Yet, control and regulation of the expression of Fam20 C are still unknown.In this study, we generated a transgenic reporter model which expresses green fluorescence protein (GFP) driven by the Fam20 C promoter. Recombination was used to insert a 16 kb fragment of the mouse Fam20 C gene (containing the 15 kb promoter and 1.1 kb of exon 1) intoa pBluescript SK vector with the topaz variant of GFP and a bovine growth hormone polyadenylation sequence. GFP expression wasted evaluated by histomorphometry on cryosections from E14 to adult mice. Fluorescence was evident in the bone and teeth as early as E17.5. The GFP signal was maintaine d stably in odontoblasts and osteoblasts until 4 weeks after birth. The expression of GFP was significantly reduced in teeth, alveolar bone and muscle by 8 weeks of age. We also observed colocalization of the GFP signal with the Fam20 C antibody in postnatal 1- and 7-day-old animals.Successful generation of Fam20C-GFP transgenic mice will provide a unique model for studying Fam20 C gene expression and the biological function of this gene during odontogenesis and osteogenesis.