Comparative ultrastructure of cells and cuticle in the anterior chamber and papillate region of Porcellio scaber (Crustacea, Isopoda) hindgut

Isopod hindgut consists of two anatomical and functional parts, the anterior chamber, and the papillate region. This study provides a detailed ultrastructural comparison of epithelial cells in the anterior chamber and the papillate region with focus on cuticle ultrastructure, apical and basal plasma membrane labyrinths, and cell junctions. Na+/K+-ATPase activity in the hindgut epithelial cells was demonstrated by cytochemical localisation. The main difference in cuticle ultrastructure is in the thickness of epicuticle which is almost as thick as the procuticle in the papillate region and only about one sixth of the thickness of procuticle in the anterior chamber. The apical plasma membrane in both hindgut regions forms an apical plasma membrane labyrinth of cytoplasmic strands and extracellular spaces. In the papillate region the membranous infoldings are deeper and the extracellular spaces are wider. The basal plasma membrane is extensively infolded and associated with numerous mitochondria in the papillate region, while it forms relatively scarce basal infoldings in the anterior chamber. The junctional complex in both hindgut regions consists of adherens and septate junctions. Septate junctions are more extensive in the papillate region. Na+/K+-ATPase was located mostly in the apical plasma membranes in both hindgut regions. The ultrastructural features of hindgut cuticle are discussed in comparison to exoskeletal cuticle and to cuticles of other arthropod transporting epithelia from the perspective of their mechanical properties and permeability. The morphology of apical and basal plasma membranes and localisation of Na+/K+-ATPase are compared with other arthropod-transporting epithelia according to different functions of the anterior chamber and the papillate region

Ultrastructural differentiation of hindgut epithelium during development of crustacean Porcellio scaber Crustacea:Isopoda)

Diferenciacija epitelnih celic ima ključno vlogo pri morfogenezi cevastih organov kot je črevo in vključuje usklajene procese, ki potekajo v skladu s fiziološkimi spremembami med razvojem. V okviru doktorske disertacije smo s kombinacijo tehnik svetlobne in elektronske mikroskopije preučili diferenciacijo epitela zadnjega črevesa med razvojem raka Porcellio scaber. Epitel zadnjega črevesa raka enakonožca P. scaber ima tipične ultrastrukturne značilnosti transportnih epitelov, ter tvori dve funkcijsko in anatomsko različni regiji. Diferenciacija črevesnih celic časovno sovpada s ključnimi razvojnimi spremembami med poznim embrionalnim in zgodnjim postembrionalnim razvojem. Gubanje apikalne plazmaleme v apikalni labirint in diferenciacija septiranih stikov sovpadata s pričetkom prehranjevanja ob izvalitvi embrijev iz notranje jajčne ovojnice. Celice zadnjega črevesa marzupijskih mank imajo tako že intenzivno povečano apikalno površino za absorpcijo prebavnih produktov in vzpostavljeno obsežno difuzijsko pregrado za uravnavan paracelularni transport. Po sprostitvi mank iz valilnika v zunanje okolje se nadaljuje diferenciacija apikalnega labirinta in septiranih stikov, oblikuje pa se tudi bazalni labirint, kar je zlasti v papilatni regiji zadnjega črevesa najverjetneje povezano s povečanimi osmoregulacijskimi zahtevami. Mikrotubuli v črevesnih celicah so urejeni v apikalno-bazalno orientirane snope, ki jih je največ v mehansko bolj obremenjenih celicah in se postopno oblikujejo med razvojem mank. Apikalna plazmalema in septirani stiki se povsem preoblikujejo med tvorbo nove kutikule ob levitvi poznih marzupijskih mank. Apikalna plazmalema se preoblikuje v nizke izrastke z elektronsko gostimi konicami, obseg septiranih stikov na lateralnih plazmalemah pa se bistveno zmanjša. Raziskave intaktnih embrijev omogočajo vpogled v diferenciacijo epitelnih celic v fiziološko relevantnem okolju celotnega organizma in s tem interpretacijo ultrastrukturnih sprememb tudi s funkcijskega vidika.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

Formation of the hindgut cuticular lining during embryonic development of Porcellio scaber (Crustacea, Isopoda)

The hindgut and foregut in terrestrial isopod crustaceans are ectodermal parts of the digestive system and are lined by cuticle, an apical extracellular matrix secreted by epithelial cells. Morphogenesis of the digestive system was reported in previous studies, but differentiation of the gut cuticle was not followed in detail. This study is focused on ultrastructural analyses of hindgut apical matrices and cuticle in selected intramarsupial developmental stages of the terrestrial isopod Porcellio scaber in comparison to adult animals to obtain data on the hindgut cuticular lining differentiation. Our results show that in late embryos of stages 16 and 18 the apical matrix in the hindgut consists of loose material overlaid by a thin intensely ruffled electron dense lamina facing the lumen. The ultrastructural resemblance to the embryonic epidermal matrices described in several arthropods suggests a common principle in chitinous matrix differentiation. The hindgut matrix in the prehatching embryo of stage 19 shows characteristics of the hindgut cuticle, specifically alignment to the apical epithelial surface and a prominent electron dense layer of epicuticle. In the preceding embryonic stage – stage 18 – an electron dense lamina, closely apposed to the apical cell membrane, is evident and is considered as the first epicuticle formation. In marsupial mancae the advanced features of the hindgut cuticle and epithelium are evident: a more prominent epicuticular layer, formation of cuticular spines and an extensive apical labyrinth. In comparison to the hindgut cuticle of adults, the hindgut cuticle of marsupial manca and in particular the electron dense epicuticular layer are much thinner and the difference between cuticle architecture in the anterior chamber and in the papillate region is not yet distinguishable. Differences from the hindgut cuticle in adults imply not fully developed structure and function of the hindgut cuticle in marsupial manca, possibly related also to different environments, as mancae develop in marsupial fluid. Bacteria, evenly distributed within the homogenous electron dense material in the hindgut lumen, were observed only in one specimen of early marsupial manca. The morphological features of gut cuticle renewal are evident in the late marsupial mancae, and are similar to those observed in the exoskeleton

Formation of the hindgut cuticular lining during embryonic development of Porcellio scaber (Crustacea, Isopoda)

The hindgut and foregut in terrestrial isopod crustaceans are ectodermal parts of the digestive system and are lined by cuticle, an apical extracellular matrix secreted by epithelial cells. Morphogenesis of the digestive system was reported in previous studies, but differentiation of the gut cuticle was not followed in detail. This study is focused on ultrastructural analyses of hindgut apical matrices and cuticle in selected intramarsupial developmental stages of the terrestrial isopod Porcellio scaber in comparison to adult animals to obtain data on the hindgut cuticular lining differentiation. Our results show that in late embryos of stages 16 and 18 the apical matrix in the hindgut consists of loose material overlaid by a thin intensely ruffled electron dense lamina facing the lumen. The ultrastructural resemblance to the embryonic epidermal matrices described in several arthropods suggests a common principle in chitinous matrix differentiation. The hindgut matrix in the prehatching embryo of stage 19 shows characteristics of the hindgut cuticle, specifically alignment to the apical epithelial surface and a prominent electron dense layer of epicuticle. In the preceding embryonic stage – stage 18 – an electron dense lamina, closely apposed to the apical cell membrane, is evident and is considered as the first epicuticle formation. In marsupial mancae the advanced features of the hindgut cuticle and epithelium are evident: a more prominent epicuticular layer, formation of cuticular spines and an extensive apical labyrinth. In comparison to the hindgut cuticle of adults, the hindgut cuticle of marsupial manca and in particular the electron dense epicuticular layer are much thinner and the difference between cuticle architecture in the anterior chamber and in the papillate region is not yet distinguishable. Differences from the hindgut cuticle in adults imply not fully developed structure and function of the hindgut cuticle in marsupial manca, possibly related also to different environments, as mancae develop in marsupial fluid. Bacteria, evenly distributed within the homogenous electron dense material in the hindgut lumen, were observed only in one specimen of early marsupial manca. The morphological features of gut cuticle renewal are evident in the late marsupial mancae, and are similar to those observed in the exoskeleton