The cell web in the ameloblasts of the rat incisor.

Abstract

AbstractThe ameloblasts (and associated cells) of adult rat incisors were examined in sections stained with tannic acid‐phosphomolybdic acid‐amino black (TPA), a method which demonstrates the fibrillar structures of cytoplasm referred to as cell web, as well as terminal bars and desmosomes. These structures were analyzed at various stages of the life cycle of ameloblasts.The first sign of a cell web is found in the immature ameloblasts observed toward the end of the proliferation zone. Delicate vertical fibrils appear, which persist in various forms throughout the zones of differentiation, secretion, post‐secretion, pigmentation and regression. These vertical fibrils are present along the lateral cell wall in most zones. In the post‐secretion zone, a coarse fiber appears in the axis of the cell within the supranuclear region. This fiber splits at both ends into fine fibrils running toward the apex and base of the ameloblast, where delicate desmosomes are visible.A first set of terminal bars arises at the base of ameloblasts in the zone of proliferation. These “basal” terminal bars persist in all except the regression zone. A second set of terminal bars appears at the apex of the ameloblasts in the zone of differentiation. These “apical” terminal bars reach their maximal development in the secretion zone and disappear in the regression zone. Finally, desmosomes are prominent in the post‐secretion and pigmentation zones, mainly on the apical and basal surfaces of the cells.The staining of terminal bars and desmosomes with TPA is presumably due to the accumulation of cell web fibrils on these attachment sites. The cell web may impart rigidity to the cell and provide resistance to stress wherever the fibrils are inserted on desmosomes and terminal bars.