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Celleutvikling og blad-mønsterdanning i tidlige stadier av Saccharina latissima sporofytter
No full textSaccharina latissima is a multicellular parenchymatic photosynthetic organism in the group of brown algae (Phaeophyceae). It belongs specifically to the group of kelps (Laminariales), a group that has recently acquired great economic and ecological importance. Notably, our knowledge for Saccharina and the other kelps is restricted to their physiological and ecological traits while our understanding on their development is mostly outdated or incomplete. Their life cycle is diplobiotic with heteromorphous generations. Specifically, the large and conspicuous plant is the sporophyte, and the microscopic stage is represented by two dioecious gametophytes. The early development of the sporophyte is a largely unknown process.
The aim of this project was to elucidate the morphogenesis of Saccharina latissima’s embryos from descriptive and mechanistic point of view. First, we identified three main phases based on the body axes of the embryo. Phase I follows the formation of the polarised zygote, characterised by a sequence of anticlinal transverse divisions perpendicular to the main growth axis. Then, longitudinal anticlinal divisions take place during Phase II, leading to the formation of a monostromatic grid made of crossaligned cuboid cells. The third growth axis is introduced during Phase III, together with the emergence of different types of tissue, a process defined as polystromatisation. Then (Paper I), a morphometric study was performed in Phase II. Morphometric quantitative parameters like cell division rate and orientation as well as cell shape and direction of expansion were collected and combined with hyperosmotic treatments to test simulations derived from vertex modelling. Simulations suggest that anisotropic patterns on cell wall (CW) stiffness explain the 2D morphogenesis of the embryo. Next (Paper II), we postulated that these patterns could be underlied by a specific organisation of the cytoskeleton. Observations on actin labelling show an anisotropic actin filaments (AFs) organisation at the cortex below the anticlinal CWs. Specifically, the cortical AFs are parallel to the future third growth axis. In contrast, the AFs below the walls of the front and rear surfaces seem isotropic. Drug treatments did not assist to establish a functional link between the CW stiffness and AF patterns. However, AFs potentially restrict cell growth along a 2D plane. We postulate that this pattern of AFs organisation needs to be rearranged for allowing cell growth and division along the three spatial axes, and therefore, to allow thickening of the so far monolayer lamina. Furthermore, we focused on the cellular and molecular events leading lamina thickening (Phase II – to – Phase III transition). At the molecular level (Paper IV), transcriptomic analysis during the initiation of Phase III detected a downregulation of most of the differentially expressed genes. In addition, GO analysis indicates a switch of gene expression towards signaling and post-translational modifications. However, a direct relation between the patterns of gene expression and the addition of a third growth axis has not been established. At the cellular level (Paper III), semithin sections elucidated the patterns of 3D growth and cell differentiation. Specifically, polystromatisation (thickening) and cell differentiation occurs centripetally from an external epidermal meristem and propagates acropetally from the base of the embryo. Different regions of the developing thallus present different morphometries and abundance of the different cell types. For example, the older polystroma is rich in medullary elements and poor in cortical cells, and the inverse is observed in younger polystroma.
My project formulates a morphogenetic model for Saccharina’s embryos, based on simple cellular mechanics. Anisotropic patterns explain how the embryos acquire their initial shape which is the scaffold for the late 3D growth accompanied by tissue emergence and a superficial meristem.Saccharina latissima est un organisme photosynthétique multicellulaire parenchymateux du groupe des algues brunes (Phaeophyceae). Elle appartient spécifiquement au groupe des kelps (Laminariales), qui a récemment fait l’objet d’un intérêt croissance au niveau économique et écologique. Nos connaissances sur Saccharina et les autres laminaires sont limitées à leurs caractéristiques physiologiques et écologiques, et notre compréhension de leur développement est pour la plupart ancienne ou incomplète. Leur cycle de vie est diplobiontique avec des générations hétéromorphes. Plus précisément, la phase du cycle la plus grande et la plus visible est le sporophyte et le stade microscopique est représenté par deux gamétophytes dioïques. Le développement précoce du sporophyte est un processus largement inconnu.
Le but de ma thèse était d’identifier les mécanismes impliqués dans la morphogenèse des embryons de Saccharina latissima , essentiellement sur le plan mécanique. Tout d'abord, nous avons identifié trois phases principales basées sur les axes de croissance des embryons. La Phase I correspond la formation de l’axe apico-basal (X) du zygote, puis du jeune embryon par une séquence de divisions transversales anticlinales perpendiculaires à l'axe longitudinal du zygote. Ensuite, des divisions longitudinales anticlinales ont lieu pendant la Phase II, établissant le deuxième axe de croissance (Y) perpendiculaire au premier. La succession de divisions dans les axes X et Y conduit à la formation d'une grille monostromatique composée de cellules cuboïdes alignées en lignes et en colonnes. Le troisième axe de croissance (Z) est introduit au début de la Phase III, au cours de laquelle l’embryon s’épaissit – un processus nommé polystromatisation – et différents types de tissus se différencient.
Dans un deuxième temps de ma thèse, une étude morphométrique a été réalisée au stade Phase II (Paper I). Des paramètres quantitatifs morphométriques tels que le taux et l'orientation des divisions cellulaires ainsi que la forme des cellules et la direction de la croissance cellulaire ont été collectés. De plus, des traitements hyperosmotiques ont été effectués sur les embryons de S. latissima pour estimer d’éventuelles anisotropies mécaniques. Ces données quantitatives biologiques ont « nourri » un modèle de type « vertex model » bidimensionnel (2-VM). Le résultat des simulations suggère que l’anisotropie de la rigidité de la paroi cellulaire (CW) dans les axes X et Y peut rendre compte de la morphogenèse 2D de l'embryon. Ensuite (Paper II), nous avons caractérisé l’organisation du cytosquelette pour évaluer dans quelle mesure elle pouvait jouer un rôle dans la morphogenèse de l’embryon. Les observations sur le marquage de l'actine montrent une organisation anisotrope des filaments d'actine (AFs) au niveau du cortex le long des parois anticlinales. Notamment, les AFs corticaux sont parallèles au futur et troisième axe de croissance. En revanche, l’organisation des AFs localisés le long des parois cellulaires « avant » et « arrière » semble isotropes. Les traitements aux drogues déstabilisant les AFs n'ont pas permis d'établir un lien fonctionnel entre la rigidité des MC et l’organisation des AFs. Cependant, les AFs limitent potentiellement la croissance cellulaire le long d'un plan 2D. Nous postulons que la croissance et la division cellulaires dans les trois axes de l’espace, et en particulier l’épaississement de la lame monocouche, nécessitent une ré-organisation des AFs.
Tester cette hypothèse nécessite de mieux comprendre les événements cellulaires et moléculaires à l’origine de la polystromatisation. Ainsi, dans un troisième temps de ma thèse, j’ai entamé une analyse transcriptomique pendant la transition de la Phase II à la Phase III de l’embryogenèse (Paper IV). J’ai détecté une régulation négative de la plupart des gènes différentiellement exprimés. En outre, l'analyse GO indique un changement de l'expression des gènes vers la signalisation et les modifications post-traductionnelles. Cependant, une relation directe entre les modèles d'expression génique et l'ajout d'un troisième axe de croissance n'a pas été établie. Par ailleurs, j’ai effectué des coupes semifines dans le but d'élucider les patrons de croissance 3D et de différenciation cellulaire au moment du changement d’axes de croissance de la monocouche (X-Y) à son épaississement (X-Y-Z) (Paper III). J’ai décrit que la polystromatisation et la différenciation cellulaire se produisent de manière centripète à partir d'un méristème épidermique externe et se propagent de manière acropète à partir de la base de l'embryon. Des différences dans la forme et l’abondance des différents types cellulaires sont observées en fonction des régions de l’embryon. Par exemple, le polystroma le plus ancien est riche en éléments médullaires et pauvre en cellules corticales, et l'inverse est observé dans le polystroma le plus jeune.
En résumé, mon projet apporte les premiers éléments sur le rôle potentiel des forces mécaniques dans le patron de croissance de la lame monocouche de l’embryon S. latissima et sur le changement d’orientation de croissance cellulaire au moment de la polystromatisation. La mise en place d’anisotropies mécaniques au niveau de la paroi et d’anisotropie dans l’organisation du cytosquelette apparaît globale et homogène à l’échelle de l’embryon
PEGASUS - Phycomorph European Guidelines for a SUstainable Aquaculture of Seaweeds
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Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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