Aspects ultrastructuraux et fonctionnels de diverses régions cuticulaires non minéralisées d'un crustacé décapode, Carcinus maenas

peer reviewe

Distribution et importance quantitative de la chitine dans les coquilles de mollusques

1. The wide distribution of chitin in the shells of Molluscs was confirmed thanks to the application of a quantitative and specific enzymatic method. Chitin was found not only in Cephalopod shells, but also in mother-of-pearl, pseudonacreous layers, and in many cases, in periostracum and prismatic layers of Gastropod and Bivalve shells. 2. The presence and the proportion of chitin are highly variable in the periostracum of the Bivalve species studied so far. On the Contrary, its permanent presence in the organic matrix, associated with mother-of-pearl, emphasizes the homology of this structure in the whole phylum nof Mollusca. 3. The more or less important participation of chitin in the vbuilding of the organic matrix of the different shell structures may be related to taxonomic and/or ecological characteristics. From a taxonomical point of view, on the one hand, chitin distribution is in good agreement with the classification grouping Arcidae and Glycimeridae among the Filibranchia Taxodonta and isolating Nuculidae in the Protobranchia. On the other hand, the lower rate of chitin observed in the inner calcified shell layers of seven species of Anisomyaria and the high chitin rate in those of four species of Adapedonta may be a further indication of the homogeneity of both taxa. From an ecological point of view, chitin constitutes an important fraction of the shell organic matter in burrowing species, while this polysaccharide is practically lacking or in very low proportions in the shells of fixed or free species.1. Au moyen d'une méthode enzymatique hautement spécifique, la chitine a été mise en évidence et dosée chez toute une série de Mollusques, non seulement chez les Céphalopodes et au niveau de structures où sa présence était déjà connue, mais aussi dans la nacre d'autres types de strates calcifiées de la coquille de diverses espèces de Lamellibranches et de Gastéropodes ainsi que, dans certains cas, au niveau des couches de prismes et du périostracum. 2. Le périostracum diffère considérablement, chez les espèces étudiées, sous le rapport de la présence de chitine et de son importance quantitative relative. Par contre, la chitine est toujours présente dans la matrice organique de la nacre, ce qui pourrait confirmer le caractère d'homologie de cette structure à travers le phylum des Mollusques. 3. La participation de la chitine à la constitution de la matrice organique des coquilles de Bivalves peut être interprétée sous l'angle taxonomique ou écologique. D'un point de vue taxonomique, la constitution chimique du périostracum d'une part est en bon accord avec l'isolement des Nuculidae au sein des Protobranchiés, et avec le regroupement des Arcidae et des Glycimeridae parmi les Filibranchiés Taxodontes. D'autre cpart, les Adapédontes se caractérisent par une plus forte proportion de chitine dans les strates calcifiées de la coquille que chez les Anisomyaires. D'un point de vue écologique, c'est chez les espèces fuisseuses (Adapédontes, mais aussi Venus, Arca, Glycimeris) que la chitine est un constituant quantitativement important de la matrice organique du périostracum et/ou des strates calcifiées internes. Chez les espèces fixées ou libres, au contraire, la chitine manque ou n'est présente qu'en faible proportion

Structure, synthèse et dégradation des chitinoprotéines de la cuticule des Crustacés décapodes

peer reviewedThe procuticle of the Crustacea Decapoda is formed of stacked laminae composed of fibre beds in which the fibres run parallel to the surface and undergo a slight and progressive change in orientation from one bed to another. The basic structural unit of the procuticle is a microfibril made up of a core of chitin criystallite surrounded by a protein sheath. Microfibrils arise at the surface of plasmamembrane plaques which are concerned with their deposition and orientation. According to the degree of mineralization, microfibrils are either homogeneously distributed (membranous layer) or secondarily associated into reticulate structures (pigmented layer) or into macrofibres (principal layer). In the newly secreted procuticular sheets the chitin-proteic fibres are disposed around long vertical microvilli originating from the epidermis. The plasmamembrane of the microvilli appears to be closely concerned with the deposition of fibrous components running vertically. Progressively the microvilli degenerate and leave hollow twisted tubes, the cuticular canals (pore canals), delimited by a helical fibre sheath. These canals may project lateral connections and constitute routes through which material involved in cuticle hardening can gain access to the external laminae. The membranous layer, deposited a long time after ecdysis, is not mineralized and exhibits a peculiar chemical composition as well as hygroscopic properties. It keeps hydrolytic enzymes in store during the preecdysial period and plays the role of lubrificating agent at the critical moment of ecdydis. The enzymatic degradation of the old cuticle during the preecdysial period is characterized by an important decrease of chitin and soluble protein contents. In contrast, the cuticular calcium is not reabsorbed, at least in Cancer pagurus and Carcinus maenas

Ultrastructural organization and chemical composition of the mineralized cuticle of Glomeris marginata (Myriapoda, Diplopoda)

peer reviewe

Human periodontal ligament fibroblast behavior on chemically conditioned dentine: an in vitro study.

BACKGROUND: Chemical root conditioning is widely used in an attempt to improve the outcome of regenerative periodontal surgery, but its effect on connective tissue cell proliferation and biosynthetic activity has been poorly studied. The goal of the present study was to test in vitro the consequences of conditioning human dentine by citric acid or minocycline on the behavior of attached human periodontal ligament (HPDL) cells in terms of proliferation, protein synthesis and morphological appearance. METHODS: HPDL cells were seeded on powdered human dentine, either untreated or conditioned for 3 minutes with 3% citric acid or 2.5% minocycline HCI. Scanning (SEM) and transmission (TEM) electron microscopic observations were performed, and 3H-thymidine and 3H-proline incorporation tests were used to evaluate the proliferative and the biosynthetic activities. RESULTS: Cell spreading was already evident and the penetration of cytoplasmic processes into dentinal tubules were frequently observed on all dentine types after 2 hours of attachment. After 24 hours of incubation, citric acid conditioning promoted an intense spreading of the cells, while minocycline HCI conditioning induced the formation of a dense feltwork of cellular processes. HPDL fibrolasts adherent to both types of surface-conditioned dentine exhibited a significantly higher rate of proliferation (P<0.01) as well as a significantly higher level of total protein and of collagen synthesis (P<0.01) than on untreated dentine. CONCLUSIONS: These data suggest that during periodontal surgery a conditioning of the root surface by citric acid or by minocycline HCI could promote the attachment, the proliferation, and the biosynthetic activity of HDPL, prerequisites to periodontal regeneration

Cytochemical investigation on tunic morphogenesis in the sea-peach Halocynthia papillosa (Tunicata, Ascidiacea). 2. Demonstration of proteins.

peer reviewe