MSX1 and tooth agenesis: Although Msx1 is essential for normal tooth development, it is dispensable for the formation of supernumerary teeth in K14-Cre8Brn; Apccko/cko mice, which suggests that Apc escapes the Msx1–Bmp4 feedback loop to rescue tooth germ arrest and facilitates its development to more advanced stages.88 Sostdc1 (ectodin, Wise and USAG1) is another candidate protein for molecular targeted therapy of tooth agenesis.