Littérature scientifique sur le sujet « Nagariensis »

In order to understand changes in cyclic adenylate levels of Volvox carteri during the process of sexual induction, we investigated the biochemical properties of its membrane-bound adenylyl cyclase. Membrane preparations possess low levels of Mg2+ -dependent or Mn2+ -dependent adenylyl cyclase activity. This activity was solubilised and then purified 7800-fold. The enzyme detergent complex has an apparent molecular mass of 100 kDa. Purified preparations contain a major ATP-binding protein of 33 kDa as shown by affinity labelling. The Mg2+ -dependent basal enzyme activity is regulated by Ca2+, and is highest in the presence of 10-7 M Ca2+, but is inhibited by Ca2+ above 10-5 M. La3+ at 10-4M also blocks activity. Neither calmodulin nor its antagonists affect the enzyme activity, nor do the purified preparations interact with immobilised calmodulin. Further mediators of G-protein action (NaF, or GTP and its derivatives) and forskolins have no influence on the basal activity of this plant enzyme. The function of adenylyl cyclase in sexual induction of Volvox is discussed.

The structure of the extracellular matrix (ECM) of representatives of all four sections of the genus Volvox was examined by a combination of light- and electron-microscopic methods. On the basis of these observations, plus published descriptions of aspects of ECM organization in other members of the order Volvocales, a system of nomenclature is proposed, to facilitate discussion of comparative morphology and phylogeny of the ECM in the order. In this system the ECM is divided into four main zones: the flagellar zone (FZ), which consists of attachments to and specializations of the ECM around the flagella; the boundary zone (BZ), which consists of portions of the ECM that (except in periflagellar regions) are continuous over the surface of the organism and are not structurally continuous with deeper layers; the cellular zone (CZ), which consists of specializations, other than those of the FZ, around individual cells; and the deep zone (DZ), which consists of components that fill the central region of the organism, internal to CZ. An empirically based set of hierarchical subdivisions of these zones is then proposed that permits specific identification of most morphologically distinct ECM components. The fact that not all zones and subzones are present in all members of the order means that this system permits identification of those ECM structures that have been gained or lost during Volvocalean evolution. Species-specific differences in the structure of virtually all aspects of the ECM were seen among the Volvox species examined in this study. However, the fact that such differences cannot always be used as diagnostic characters for the four divisions of the genus was demonstrated by the observation that in certain ECM features two members of the same division (V. carteri f. nagariensis and V. carteri f. weismannia) differ markedly in structure from one another, with one member of the pair resembling a member of another division. Thus many details of ECM organization appear to be under separate control, and capable of independent evolution.

V. carteri f. nagariensis est un modèle établi pour l'étude des bases génétiques à l'acquisition de la multicellularité et la différenciation cellulaire. Cette algue constitue, une sphère structurée autour et stabilisée par une matrice extracellulaire primitive. Employant sa capacité à supporter l'adhésion cellulaire, j’ai développé une approche modulaire d'ingénierie des tissus mous par empilement compact de colonies de V. carteri. L’algue a démontré une cytocompatibilité, une promotion de l'histogenèse et une réponse non inflammatoire in vitro permettant d'envisager l'utilisation de V. carteri pour l'augmentation des tissus mous et lancer l’étude de sa biocompatibilité in vivo. Elle a présenté des propriétés de direction du devenir cellulaire, amenant les fibroblastes à adopter un phénotype de cellules souches à phosphatase alcaline+ et les cellules souches humaines et les cellules souches embryonnaires murines à se différencier en préadipocytes à adipocytes. Ses capacités de soutien de l'histogenèse et l'adipogenèse ont été confirmées in vivo par augmentation de tissu en sous-cutané sur souris athymiques, soutenant et influençant la régénération tissulaire. V. carteri a inspiré le développement d’autres matériaux alternatifs, d'origine végétale sous la forme d'hydrogel composite à base de cellulose caractérisé de manière approfondie pour l'augmentation des tissus mous. J’ai poursuivi l'approche biomimétique par l’étude de la faisabilité de formation d’un matériau végétal ou incluant l’algue, déclinant sa morphologie de microsphère et son contenu protéiques. Notre conclusion présente V. carteri comme un biomatériau innovant et inspirant pour l'ingénierie tissulaire et la régénération des tissus mous. Sa forme, sa structure et sa composition pourraient jouer un rôle central dans la conception d'une nouvelle génération de biomatériaux hétérogènes bio-inspirés, reflétant la complexité des tissus de l'organisme lors de leur régénération
V. carteri f. nagariensis is an established model for the study of the genetic basis underlying the acquisition of mechanisms of multicellularity and cellular differentiation. This microalga constitutes, in its most simplified form, a sphere built around and stabilised by a form of primitive extracellular matrix. Based on its structure and its ability to support surface cell adhesion most likely induced by the composition of its extracellular matrix, we have developed a modular approach to soft tissue engineering by compact-stacking of V. carteri colonies. V. carteri suspension demonstrated cytocompatibility, histogenesis promoting properties, and no induction of an inflammatory response in vitro, which allowed us to consider the use of V. carteri suspension colonies for soft tissue augmentation and to initiate the study of its in vivo biocompatibility. V. carteri exhibited cellular fate-directing properties,causing fibroblasts to take on an alkaline phosphatase+ stem-cell-like phenotype and both human adipose-derived stem cells and mouse embryonic stem cells to differentiate into preadipocytes to adipocytes. The ability of V. carteri to support histogenesis and adipogenesiswas also observed in vivo by subcutaneous tissue augmentation of athymic mice, highlighting the potential of V. carteri to support or influence tissue regeneration. The potential identified in V. carteri inspired us to develop other alternatives materials including plant-based polymers in the form of a cellulose and polyvinyl alcohol based composite hydrogel that we extensively characterised with the same intent of application as a substitute for soft tissue augmentation. We finally pursued the biomimetic approach by studying the feasibility of developing plant-based and V. carteri-based materials that would display its microsphere morphology and, additionally, its protein content. Our conclusion presents V. carteri as an innovative and inspiring biomaterial for tissue engineering and soft tissue regeneration. Its strategies in terms of shape, structure, and composition can be central in the design of a new generation of bio-inspired heterogeneous biomaterials, recapitulating more appropriately the complexity of the body tissues when guiding their regeneration