Figure 9: Hypothetical model. NUMB regulates stem cell properties at two levels. NUMB downregulates the expression of the activated Notch 1 protein level in the progenitor cells at the cervical loop and thereby inhibits the Shh expression in the adjacent preameloblasts. Thus, NUMB influences the expression of downstream genes such as Notch1 and Shh and thus performs critical role in ameloblast differentiation.