1,720,979 research outputs found
Alterations in the protein kinase C signaling activated by a parthenogenetic agent in oocytes from reproductively old mice
No full textBackground: Mammalian sperm-oocyte interaction at fertilization involves several combined interactions
between integrins on the oocyte and integrin ligands (disintegrins) on the sperm. Recent research has
indicated the ability of peptides containing the RGD sequence that characterized several sperm
disintegrins, to induce intracellular Ca2+ transients and to initiate parthenogenetic development in
amphibian and bovine oocytes. In the present study, we investigate the hypothesis that an integrinassociated
signalling may participate in oocyte activation signalling by determining the ability of a cyclic
RGD-containing peptide to stimulate the activation of protein kinase C (PKC) and the exocytosis of
cortical granules in mouse oocytes.
Methods: An In-Vitro-Fertilization assay (IVF) was carried in order to test the condition under which a
peptide containing the RGD sequence, cyclo(Arg-Gly-Asp-D-Phe-Val), was able to inhibit sperm fusion
with zona-free mouse oocytes at metaphase II stage. PKC activity was determined by means of an assay
based on the ability of cell lysates to phosphorylate MARKS peptide, a specific PKC substrate. Loss of
cortical granules was evaluated by measuring density in the oocyte cortex of cortical granules stained with
LCA-biotin/Texas red-streptavidin. In all the experiments, effects of a control peptide containing a non
RGD sequence, cyclo(Arg-Ala-Asp-D-Phe-Val), were evaluated.
Results: The IVF assay revealed that the fusion rate declined significantly when insemination was carried
out in the presence of cyclic RGD peptide at concentrations > or = 250 microM (P < 0.05, Student-
Newman-Keuls Method). When the peptide was applied to the oocytes at these concentrations, a dosedependent
increase of PKC activity was observed, in association with a loss of cortical granules ranging
from 38+/-2.5 % to 52+/-5.4 %. Evaluation of meiotic status revealed that cyclic RGD peptide was
ineffective in inducing meiosis resumption under conditions used in the present study.
Conclusion: The presents results provide evidence that a cyclic RGD peptide highly effective in inhibiting
sperm-oocyte interaction stimulates in mouse oocytes the activation of PKC and the exocytosis of cortical
granules. These data support the view that RGD-binding receptors may function as signalling receptors
giving rise integrated signalling not sufficient for a full oocyte activation response. This study may
contribute to the understanding of possible negative effects of skipping gamete interaction in IVF
techniques
L’invecchiamento dell'ovocita: possibile ruolo del metilgliossale, una molecola citotossica prodotta dal metabolismo cellulare
No full textPossible involvement of integrin-mediated signalling in oocyte activation: evidence that a cyclic RGD-containing peptide can stimulate protein kinase C and cortical granule exocytosis in mouse oocytes
No full textAbstract Background Mammalian sperm-oocyte interaction at fertilization involves several combined interactions between integrins on the oocyte and integrin ligands (disintegrins) on the sperm. Recent research has indicated the ability of peptides containing the RGD sequence that characterized several sperm disintegrins, to induce intracellular Ca2+ transients and to initiate parthenogenetic development in amphibian and bovine oocytes. In the present study, we investigate the hypothesis that an integrin-associated signalling may participate in oocyte activation signalling by determining the ability of a cyclic RGD-containing peptide to stimulate the activation of protein kinase C (PKC) and the exocytosis of cortical granules in mouse oocytes. Methods An In-Vitro-Fertilization assay (IVF) was carried in order to test the condition under which a peptide containing the RGD sequence, cyclo(Arg-Gly-Asp-D-Phe-Val), was able to inhibit sperm fusion with zona-free mouse oocytes at metaphase II stage. PKC activity was determined by means of an assay based on the ability of cell lysates to phosphorylate MARKS peptide, a specific PKC substrate. Loss of cortical granules was evaluated by measuring density in the oocyte cortex of cortical granules stained with LCA-biotin/Texas red-streptavidin. In all the experiments, effects of a control peptide containing a non RGD sequence, cyclo(Arg-Ala-Asp-D-Phe-Val), were evaluated. Results The IVF assay revealed that the fusion rate declined significantly when insemination was carried out in the presence of cyclic RGD peptide at concentrations > or = 250 microM (P Conclusion The presents results provide evidence that a cyclic RGD peptide highly effective in inhibiting sperm-oocyte interaction stimulates in mouse oocytes the activation of PKC and the exocytosis of cortical granules. These data support the view that RGD-binding receptors may function as signalling receptors giving rise integrated signalling not sufficient for a full oocyte activation response. This study may contribute to the understanding of possible negative effects of skipping gamete interaction in IVF techniques.</p
Ultrastructural apects of naturally occurring wound in the tunic of two ascidians: Ciona intestinalis and Styela plicata (Tunicata)
No full textEfficient wound healing is essential for all animals from insects to mammals. Ciona intestinalis and Styela plicata are solitary ascidians belonging to urochordates, a subphylum that occupies a key phylogenetic position as it includes the closest relative to vertebrates. Urochordate first physical barrier against invaders is the tunic, an extracellular matrix that is constantly exposed to all kinds of insults. Thus, when damage occurs, an innate immune response is triggered to eliminate impaired tissue and potentially pathogenic microbes, and restore tissue functionality. Ultrastructural aspects of the tunic in the wound healing process of two ascidians are described. In the injured areas, we evidenced thinning of the tunic and areas of low fibre density, dense intratunic bacterial and protozoan population, and inflammatory aspects such as the increase in tunic cells, their aggregates, and phagocytosis. This is the first report on tunic physical wounding occurring in the natural habitat
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
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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