FIGURE 10.

Hypothetical model for the initiation of AP-2, clathrin-mediated endocytosis of the degraded enamel matrix protein (EMP) debris in maturation ameloblasts. It is apparent that greater endocytotic activity is seen in the maturation ameloblasts, when compared with secretory ameloblasts. Endocytosis is likely a feature of both the ruffle-ended (RA) and smooth-ended (SA) ameloblasts. The figure illustrates that the endocytotic uptake may be initiated by direct receptor-ligand interaction, such as the EMP debris interacting directly with LAMP1, LAMP2, or CD63. Alternatively, EMP debris may bind to another EMP protein, such as TF, and then this complex may bind to the TFRC to initiate the uptake of the extracellular enamel matrix peptides. A dark gray double capsule represents a tight junctional complex at the apical region of RA, and a light gray double capsule represents a “leaky” junctional complex at the apical region of SA.