1,720,971 research outputs found
Gravity sensing by cells: mechanisms and theoretical grounds
No full textSpaceflight technologies have disclosed amazing opportunities to outreach human knowledge and control over the natural world. However, the actual experience of microgravity has become a relevant threat that significantly limits the extent of man permanence in space. Since then, gravity effects on living organisms became a critical field of investigation. Gravity has been proven to affect a wide array of biological functions, interacting at different levels of complexity, from molecules to cells, tissue and the organisms as a whole. However, it is still a matter of investigation if gravity induces direct or indirect effects on cells. The non-equilibrium theory has been proven to explain how biological dissipative structures, like the cytoskeleton, may be sensitive enough to sense gravity change, then transferring the mechano-signal into biochemical pathways. Within that framework, gravity represents an 'inescapable' constraint that obliges living beings to adopt only a few configurations among many others. By removing the gravitational field, living structures will be free to recover more degrees of freedom, thus acquiring new phenotypes and new properties. Discoveries on that field are thought to advance our knowledge, providing amazing insights into the biological mechanism underlying physiology as well as many relevant diseases
Gravity constraints drive biological systems toward specific organization patterns. Commitment of cell specification is constrained by physical cues
No full textDifferent cell lineages growing in microgravity undergo a spontaneous
transition leading to the emergence of two distinct phenotypes. By returning
these populations in a normal gravitational field, the two phenotypes
collapse, recovering their original configuration. In this review, we hypothesize
that, once the gravitational constraint is removed, the system freely
explores its phenotypic space, while, when in a gravitational field, cells are
“constrained” to adopt only one favored configuration. We suggest that the
genome allows for a wide range of “possibilities” but it is unable per se to
choose among them: the emergence of a specific phenotype is enabled by
physical constraints that drive the system toward a preferred solution. These
findings may help in understanding how cells and tissues behave in both
development and cancer
Physical constraints in cell fate specification. A case in point. Microgravity and phenotypes differentiation
No full textData obtained by studying mammalian cells in absence of gravity strongly support the notion that cell
fate specification cannot be understood according to the current molecular model. A paradigmatic case in
point is provided by studying cell populations growing in absence of gravity. When the physical
constraint (gravity) is ‘experimentally removed’, cells spontaneously allocate into two morphologically
different phenotypes. Such phenomenon is likely enacted by the intrinsic stochasticity, which, in turn, is
successively ‘canalized’ by a specific gene regulatory network. Both phenotypes are thermodynamically
and functionally ‘compatibles’ with the new, modified environment. However, when the two cell subsets
are reseeded into the 1g gravity field the two phenotypes collapse into one. Gravity constraints the
system in adopting only one phenotype, not by selecting a pre-existing configuration, but more precisely
shaping it de-novo through the modification of the cytoskeleton three-dimensional structure. Overall,
those findings highlight how macro-scale features are irreducible to lower-scale explanations. The
identification of macroscale control parameters e as those depending on the field (gravity, electromagnetic
fields) or emerging from the cooperativity among the field's components (tissue stiffness, cellto-
cell connectivity) e are mandatory for assessing boundary conditions for models at lower scales, thus
providing a concrete instantiation of top-down effects
Going 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
LIGHT AND ELECTRON MICROSCOPY UNVEIL MORPHOLOGICAL CHANGES IN ART-DERIVED HUMAN OOCYTES CULTURED IN WEIGHTLESSNESS CONDITION
No full textThe effects of weightlessness on human oocyte maturation and competence to fertilization have not been
investigated up to now. Our aim was to study, by light and transmission electron microscopy (LM and
TEM) the morphology of human oocytes under simulated microgravity. As preliminary results we reported
here in data on fifteen metaphase II (MII) oocytes, obtained from patients undergoing ART treatments.
Ten oocytes were grown on simulated microgravity (~0g) through Random Positioning Machine (RPM)
and prepared for LM and TEM examination after 24 hours of culture. Five oocytes were kept as controls.
Both groups contained enclosed and free cumulus oocytes. By LM, shape of both oocyte groups looks like
well rounded. However, a small percentage of microgravity-cultured oocytes (20%) showed an irregular
contour. Organelles (mitochondria, mitochondria-smooth endoplasmic reticulum aggregates, and
mitochondria-vesicle – MV- complexes) were uniformly distributed in all TEM examined samples.
Mitochondria were typically rounded and provided with peripheral, arched cristae in all but one oocyte,
where dumb-bell shaped or crescent-shaped (dividing?) mitochondria were also found. In addition, MV
complexes appeared enlarged in numerous microgravity-cultured oocytes (66%). In most samples, cortical
granules (CGs) were uniformly distributed, just beneath the oolemma. CGs located in the inner ooplasm
were also found in 20% of microgravity-grown oocytes. One oocyte presumably underwent activation
during microgravity exposure, appearing as a two-cell egg, completely devoid of CGs. Finally, we did not
evidenced ultrastructural differences between cumulus-enclosed and cumulus-free oocytes. In
conclusion, a certain proportion of human MII ART oocytes in RPM showed significant alteration in both
shape as well as in the morphology of sub-cellular organelles. However, abnormal features - possibly
induced by microgravity - such as organelle clustering, presence of irregularly shaped mitochondria,
presence of abnormally large MV complexes, CG relocation in the inner ooplasm and oocyte activation -
deserve to be further investigated
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
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe 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
Full text linkWe 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
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