1,721,139 research outputs found
ORGANIZZAZIONE DEL CITOSCHELETRO, ESPRESSIONE EDISTRIBUZIONE INTRACITOPLASMATICA DI STAUFEN(RNA-BINDING PROTEIN) E CALRETICULINA IN OVOCITIUMANI DURANTE IL PROCESSO MATURATIVO
No full textBefore the mammalian oocyte engages in the fertilization process, it must acquire an array of molecular and cellular assets defining its developmental potential. These properties specify competencies to complete meiosis and initiate mitosis. Meiotic maturation requires the acquisition both of nuclear and cytoplasmic competence and this complex mechanism involves most of the organelles, the cytoskeleton and molecules that are relocated from the nucleus to the cytoplasm. Messenger RNAs of maternal origin are accumulated in the oocyte throughout its growth in the ovary. These transcripts are then shuttled to specific sites of the ooplasm, where local translation is promoted. The oocyte maturation marks the beginning of this phase of activation of maternal transcripts and proteins and involves the "unmasking" of maternal mRNA concomitantly to post-translational changes of stored proteins. This process loosens the stabilization mechanisms that had been imposed during oogenesis. At the end of this route maternal information will be available to the developing embryo. In this scenario, Staufen RNA Binding Protein may play an important role in the light of its function of vector of mRNAs from the nucleus to the sites of translation. Therefore, we hypothesized that Staufen is expressed during oocyte maturation and that the localization of Staufen protein changes during the meiotic transition from GV to MII. We also postulated that the pattern of Staufen distribution reflects its physical interaction with the endoplasmic reticulum, an organelle directly involved in the process of mRNA translation whose relocalization is central to the process of oocyte maturation. To test the above hypotheses, we assessed the expression of Staufen and Calreticulin (CALR), the latter adopted as a marker of the endoplasmic reticulum, in human oocytes at different stages of maturation: GV, MI and MII. The oocytes were obtained from supernumerary material of assisted reproductive cycles and were subjected to polymerase chain reaction in order to investigate the expression of Staufen, CALR and related RNAs. The corresponding protein products were identified by immunofluorescence and confocal laser scanning microscopy. Our findings indicate that Staufen and CALR are constantly expressed and selectively localized during oocyte maturation. The different pattern of Staufen distribution at the GV, MI and MII stages implicates that localization of protein translation is one of the levels at which gene expression is regulated in the maturing oocyte. On the other hand, localization of CALR at the MII stage reveals novel aspects of physical interaction with the MII spindle and suggests a previously unrecognised role of the endoplasmic reticulum in support of cytoskeletal function in the human oocyte
Le istituzioni bilaterali tra legge e contrattazione collettiva: note di sintesi e prospettive
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Studio dei fenomeni tribologici di base Comportamento a secco di tre tipici acciai in atmosfere a tenori di ossigeno variabili
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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
Changes of Large-Scale Chromatin Configuration During Mammalian Oocyte Differentiation
No full textMammalian oocyte development is characterized by impressive dynamic changes in chromatin structure and function within the germinal vesicle (GV). During meiotic arrest at diplotene stage, and particularly during the oocyte growth phase leading to the formation of the fully-grown and dif- ferentiated oocyte, the chromatin enclosed within the GV is subjected to several levels of regulation controlling both its structure and function. Morphologically, the chromosomes lose their individuality and form a loose chromatin mass, which in turn undergoes profound and dynamic rearrangements within the GV before the meiotic resumption. These large- scale chromatin configuration changes have been studied in several mam- mals and progressive condensation of the chromatin has been related to the achievement of meiotic and developmental potential. In this chapter we will give an overview of the scientific literature on this topic, highlight- ing how changes in chromatin configurations are related to both functional and structural modifications occurring in the oocyte nuclear and cytoplas- mic compartments. Further, we will discuss the machinery regulating this complex process, including the fundamental role exerted by the follicular cells also throughout intracellular messenger dependent mechanism(s). Finally, we will discuss possible implications for the field of assisted reproductive technologies
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