The biological activities of polypeptide growth factors are specifically regulated by various binding proteins. Follistatin has been shown to bind and neutralise many members of the transforming growth factor
b (TGF-
b) superfamily, including Activin, BMP, and GDF. Follistatin knockout mice died at birth and had defects in muscle, bone, skin, hair follicle, and tooth. Objective: The aim of this study was to investigate the potential role of follistatin during tooth development. Methods: We analysed tooth abnormalities in follistatin knockout mice and in transgenic mice overexpressing follistatin under keratin 14 promoter. The molar tooth morphology was analysed from serial histological sections (knockout mice) and macroscopically (K14-follistatin mice). The expression of ameloblast and odontoblast marker genes were compared in mutant and wild type mice by using
in situ hybridisation and immunohistochemistry. Mutant tooth germs were also cultured
in vitro for further developmental assay. Results: Both follistatin deficiency and overexpressing mice have misshapen molars. Follistatin knockout mice generate functional ameloblasts on the lingual side of incisors, which is the root analogue area without any enamel formation in wild type mice. Conclusions: Our results indicate that follistatin regulates cusp formation and cell differentiation of the developing teeth. The presence of ameloblasts on the lingual surface of follistatin mutant incisors suggests that follistatin normally inhibits ameloblast differentiation and is responsible for the formation of enamel-free area in mouse teeth. These data suggest important roles of TGF-
b superfamily growth factors and their inhibitors in the regulation of enamel formation and root development.