1,720,998 research outputs found
Distribution of proliferating cells and vasa-positive cells in the embryo of Macrostomum lignano (Rhabditophora, Platyhelminthes)
No full textThe neoblast stem cell system of flatworms is considered to be unique within the animal kingdom. How this stem cell system arises during embryonic development is intriguing. Therefore we performed bromodeoxyuridine labelling on late stage embryos of Macrostomum lignano to assess when the pattern of proliferating cells within the embryo is comparable to that of hatchlings. This pattern can be found in late embryonic stages (stage 8). We also used the freeze cracking method to perform macvasa embryonic labelling. Macvasa is a somatic and germ line stem cell marker. We showed macvasa protein distribution during the whole embryonic development. In the macvasa-positive blastomeres the protein is localized around the nucleus in the putative chromatoid bodies. However, at a specific embryonic stage, it is also ubiquitously present in the cytoplasm of some blastomeres. We compare our data with what is known from Schmidtea polychroa of the expression of the vasa-like gene SpolvlgA and the protein distribution of the chromatoid body component Spoltud-1. The embryonic origin of the somatic stem cell system and the germ line is discussed
Distribution of proliferating cells and vasa-positive cells in the embryo of Macrostomum lignano (Rhabditophora, Platyhelminthes)
No full textThe neoblast stem cell system of flatworms is considered to be unique within the animal kingdom. How this stem cell system arises during embryonic development is intriguing. Therefore we performed bromodeoxyuridine labelling on late stage embryos of Macrostomum lignano to assess when the pattern of proliferating cells within the embryo is comparable to that of hatchlings. This pattern can be found in late embryonic stages (stage 8). We also used the freeze cracking method to perform macvasa embryonic labelling. Macvasa is a somatic and germ line stem cell marker. We showed macvasa protein distribution during the whole embryonic development. In the macvasa-positive blastomeres the protein is localized around the nucleus in the putative chromatoid bodies. However, at a specific embryonic stage, it is also ubiquitously present in the cytoplasm of some blastomeres. We compare our data with what is known from Schmidtea polychroa of the expression of the vasa-like gene SpolvlgA and the protein distribution of the chromatoid body component Spoltud-1. The embryonic origin of the somatic stem cell system and the germ line is discussed
Assessment of the configuration of the posterior cells of the nematode embryo as potential phylogenetic marker
No full textWe have reconstructed the evolutionary history of an early developmental character by mapping the configuration of the posterior cells in the early embryo onto the SSU-based molecular phylogeny of Holterman (2006). We have analyzed the early embryonic development of 19 species, complemented with 20 species from the literature, covering representatives in each clade. We show that the Caenorhabditis elegans configuration, found in most species in clade III-X, is the ancestral state for these clades. alternative configurations arose inependently in clade IX, (Diploscapter coronatus), X (Halicephalobus gingivalis), XI (all investigated species) and XII (Meloidogyne incognita). A variable configuration of the posterior cells arose at least twice independently during nematode evolution, once in clade IX (D. coronatus) and once in an ancestor, shared by clade XI and XII and thus can be used as a phylogenetic marker to delineate these clades. Statistical tests based on our data-set show that the presence of a variable configuration is related to developmental tempo and egg shape
Assessment of the configuration of the posterior cells of the nematode embryo as potential phylogenetic marker
No full textWe have reconstructed the evolutionary history of an early developmental character by mapping the configuration of the posterior cells in the early embryo onto the SSU-based molecular phylogeny of Holterman (2006). We have analyzed the early embryonic development of 19 species, complemented with 20 species from the literature, covering representatives in each clade. We show that the Caenorhabditis elegans configuration, found in most species in clade III-X, is the ancestral state for these clades. alternative configurations arose inependently in clade IX, (Diploscapter coronatus), X (Halicephalobus gingivalis), XI (all investigated species) and XII (Meloidogyne incognita). A variable configuration of the posterior cells arose at least twice independently during nematode evolution, once in clade IX (D. coronatus) and once in an ancestor, shared by clade XI and XII and thus can be used as a phylogenetic marker to delineate these clades. Statistical tests based on our data-set show that the presence of a variable configuration is related to developmental tempo and egg shape
The quest for the fountain of youth : developing flatworm models for ageing and rejuvenation research
Full text linkGoing Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Embryonic origins of hull cells in the flatworm <i>Macrostomum lignano</i> through cell lineage analysis: developmental and phylogenetic implications
No full textThe development of macrostomid flatworms is of interest for evolutionary developmental biology research because these taxa combine characteristics of the canonical spiral cleavage pattern with significant deviations from this pattern. One such deviation is the formation of hull cells, which surround the remaining embryonic primordium during early development. Using live observations with a 4D microscope system, histology, and 3D reconstructions, we analyzed the ontogeny of these hull cells in the macrostomid model organism Macrostomum lignano. Our cell lineage analysis allowed us to find the precursors of the hull cells in this species. We discuss the relation between macrostomid development and the development of other spiralians and the question of whether hull cells are homologous within rhabditophoran flatworms
Variations on the Author
Full text link“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
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