Immunolocalization of enamel proteins during amelogenesis in the cat

Amelogenesis in the cat has been suggested to closely resemble enamel formation in human teeth. In order to further characterize the sequence of events leading to enamel formation in the cat, the expression and distribution of enamel proteins throughout amelogenesis were examined by postembedding immunocytochemistry using an antibody to mouse amelogenins and the high resolution protein A-gold technique. Enamel proteins were first immunodetected in ameloblasts and in the extracellular matrix during the presecretory stage. Secretory stage ameloblasts showed the most intense cellular reactivity. In these cells, protein synthetic organelles, secretory granules, and large lysosome-like structures were all intensely labeled. Extracellularly, numerous gold particles were observed over enamel and over patches of material found at the baso-lateral surfaces of these ameloblasts. During the early maturation stage, the protein synthetic organelles and secretory granules of ameloblasts still showed some immunoreactivity, although the most conspicuous labeling at this later stage was found over enamel and over material present among the extensive apical membrane infoldings of ruffle-ended ameloblasts. Qualitative analysis of lysosome-like elements in ameloblasts suggested that their frequency and immunoreactivity in the maturation stage were relatively lower than in the secretory stage, where some groups of cells often showed numerous large labeled structures. The enamel matrix was intensely labeled at all stages; however, cervical-occlusal and surface-depth gradients were readily apparent by conventional staining and by quantitative analysis of immunolabeling in the late secretory and early maturation stages. These data suggest that the cellular and extracellular distribution of enamel proteins in the cat is generally similar to that reported in other species, although some particularities were observed, perhaps reflecting variation in the timing of developmental parameters.