The distribution of enamel proteins (EP) within extracellular and subcellular compartments of the enamel organ has been characterized by use of the protein A-gold immunocytochemical technique and an antibody against mouse amelogenins. EP were immunolocalized within the protein synthetic and secretory organelles, and within lysosomal elements of ameloblasts in both the secretion and maturation stages. The results provide direct evidence that ameloblasts maintain active secretory and degradative pathways for EP throughout the secretory and early maturation stages of amelogenesis. The origin of the immunoreactive material within lysosomes is unclear and could derive from the direct shunting of newly formed EP from the synthetic organelles to the lysosomes or from endocytosis of aged proteins. These findings ultimately provide new insights into the multifunctional role which ameloblasts play throughout amelogenesis.
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