Differentiation of epithelial cells has a key role in morphogenesis of tubular organs such as the gut and involves coordinated processes that procced according to physiological changes during development. With combination of light and electron microscopic techniques we have investigated hindgut epithelium differentiation during development of crustacean Porcellio scaber. The hindgut epithelium of isopod P. scaber exhibits typical ultrastructure of transport epithelia and comprises two anatomically and functionally distinct regions. Hindgut cell differentiation temporally coincides with key developmental transitions during the late embryonic and early postembryonic development. The folding of apical plasma membrane and the differentiation of septate junctions coincide with the hatching from inner egg envelope, associated by the onset of active feeding. These changes provide increased apical surface available for the absorption of digestion products and proficient diffusion barrier for the controlled paracellular transport. After mancae are released into the external environment, the apical plasma membrane and the septate junctions are further differentiated and the basal labyrinth is established, probably in association with increased osmoregulatory demands. The microtubules in hindgut cells are arranged in apico-basally oriented bundles, which are the most abundant in mechanically burdened cells and are gradually formed during the development of mancae. During the formation of new cuticle in molting late marsupial mancae the apical plasma membrane and septate junctions are completely remodelled. The apical plasma membrane forms shallow protrusions and the septate junctions at lateral plasma membranes are considerably reduced. Studies of intact embryos provide insight into epithelial cell differentiation in physiological relevant environment of the whole organism and thus the interpretation of ultrastructural changes from the functional aspect.
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