1,720,975 research outputs found
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
Unraveling new mechanisms for nuclear positioning prior to cell migration
No full textSFRH/BD/52227/201
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
The role of nuclear positioning in muscle function
No full textSkeletal muscle is formed by multinucleated myofibers, the biggest cells in the human body. The multiple nuclei in these cells are regularly positioned so that the distance between them is maximized. It was previously found that nuclear positioning is important for skeletal muscle function (Metzger et al., 2012). However, mechanistic insight was missing since no evident structural abnormalities were found as a consequence of nuclear mispositioning. We hypothesized that each nucleus influences the nearby cytoplasm by determining mRNA localization along myofibers. As a consequence, protein translation and regulation would be hampered in situations of nuclear mispositioning, such as in centronuclear myopathies.
Using highly matured mouse myofibers differentiated in vitro, we found that overall mRNA distribution depends on nuclear position. Using smFISH we observed that during myofiber maturation and myofibril organization, mRNAs are pushed towards the sarcolemma. We also validated the nuclear domain theory (Pavlath et al., 1989) by detecting total mRNA clustering around peripheral nuclei. This seems to be the default localization of mRNAs in myofibers since both muscle specific and housekeeping transcripts display the same pattern.
This perinuclear clustering is an active mechanism, dependent on the minus end directed microtubule motor dynein and its activator dynactin. We have also established that the levels of protein translation can depend on nuclear location. Ribosome content is higher in the nuclear region, independently of Dynactin2 expression. Using a heterokaryon system, we show that at least some proteins in the cell remain localized close to their nucleus of origin. Moreover, contractibility of the cells correlates with the position of the nucleus and thus with overall mRNA localization.
Interestingly, a peculiar subset of mRNAs localizes regardless of where the nucleus is placed. A common feature of these transcripts is their extremely big length. We confirmed that this differential distribution is also happening in vivo. We propose that an active mechanism is responsible for this “giant” mRNA localization in order to ensure and facilitate the localization of the encoded proteins. Understanding the mechanisms of mRNA transport and anchoring that govern its subcellular destinations in myofibers may be the key to understand how nuclear positioning impacts muscle activity
Unravelling the role of mRNA localization mechanisms in the establishment of myofiber nuclear domains
No full textSkeletal muscle is formed by the largest cells in the human body. Muscle cells or myofibers are elongated cells with multiple nuclei evenly distributed in a manner that maximizes the distance between nuclei (Bruusgaard et al., 2003). During development, the nuclei undergo a series of movements until they reach their final position and are anchored in the cell periphery (Roman & Gomes, 2018). It was previously described that nuclear positioning is important for muscle function (Metzger et al., 2012). The spaced distribution of nuclei suggests that nuclear positioning can be relevant for the establishment of the myonuclear domains. According to this hypothesis, each nucleus within the multinucleated myofiber is responsible for a limited volume of cytoplasm. In the neuromuscular and mypotendinous junctions there is compartmentalization of specific messenger ribonucleic acids (mRNAs) and proteins, but the mRNA distribution in non specialized areas of the myofiber remains largely unexplored. In this work, we analyzed the distribution of several mRNAs important for muscle function in highly differentiated myofibers in vitro. We observed that the bulk of mRNA is enriched around the nucleus of origin. The perinuclear enrichment depends on recently transcribed mRNAs. Surprisingly, we found a subset of mRNAs that are differentially distributed. mRNAs encoding large proteins are spread throughout the cell. By exogenous expression of mRNAs with different sizes, we found that transcript size contributes to mRNA spreading in a sequence independent manner. Microtubules are involved in the distribution of normal size and large mRNAs away from the nucleus, but the effect is more evident in the distribution of large mRNAs. Additionally, we observed that the differential distribution is independent of the nuclear positioning and mRNA expression and stability. Considering our findings, we propose that mRNA distribution in non-specialized regions of skeletal muscle is size selective to ensure the distribution of mRNAs with special characteristics, such as large size, while maintaining cellular compartmentalization around each nucleus
Unravelling the role of mRNA localization mechanisms in the establishment of myofiber nuclear domains
No full textSkeletal muscle is formed by the largest cells in the human body. Muscle cells or myofibers are elongated cells with multiple nuclei evenly distributed in a manner that maximizes the distance between nuclei (Bruusgaard et al., 2003). During development, the nuclei undergo a series of movements until they reach their final position and are anchored in the cell periphery (Roman & Gomes, 2018). It was previously described that nuclear positioning is important for muscle function (Metzger et al., 2012). The spaced distribution of nuclei suggests that nuclear positioning can be relevant for the establishment of the myonuclear domains. According to this hypothesis, each nucleus within the multinucleated myofiber is responsible for a limited volume of cytoplasm. In the neuromuscular and mypotendinous junctions there is compartmentalization of specific messenger ribonucleic acids (mRNAs) and proteins, but the mRNA distribution in non specialized areas of the myofiber remains largely unexplored. In this work, we analyzed the distribution of several mRNAs important for muscle function in highly differentiated myofibers in vitro. We observed that the bulk of mRNA is enriched around the nucleus of origin. The perinuclear enrichment depends on recently transcribed mRNAs. Surprisingly, we found a subset of mRNAs that are differentially distributed. mRNAs encoding large proteins are spread throughout the cell. By exogenous expression of mRNAs with different sizes, we found that transcript size contributes to mRNA spreading in a sequence independent manner. Microtubules are involved in the distribution of normal size and large mRNAs away from the nucleus, but the effect is more evident in the distribution of large mRNAs. Additionally, we observed that the differential distribution is independent of the nuclear positioning and mRNA expression and stability. Considering our findings, we propose that mRNA distribution in non-specialized regions of skeletal muscle is size selective to ensure the distribution of mRNAs with special characteristics, such as large size, while maintaining cellular compartmentalization around each nucleus
The role of nuclear positioning in muscle function
No full textSkeletal muscle is formed by multinucleated myofibers, the biggest cells in the human body. The multiple nuclei in these cells are regularly positioned so that the distance between them is maximized. It was previously found that nuclear positioning is important for skeletal muscle function (Metzger et al., 2012). However, mechanistic insight was missing since no evident structural abnormalities were found as a consequence of nuclear mispositioning. We hypothesized that each nucleus influences the nearby cytoplasm by determining mRNA localization along myofibers. As a consequence, protein translation and regulation would be hampered in situations of nuclear mispositioning, such as in centronuclear myopathies.
Using highly matured mouse myofibers differentiated in vitro, we found that overall mRNA distribution depends on nuclear position. Using smFISH we observed that during myofiber maturation and myofibril organization, mRNAs are pushed towards the sarcolemma. We also validated the nuclear domain theory (Pavlath et al., 1989) by detecting total mRNA clustering around peripheral nuclei. This seems to be the default localization of mRNAs in myofibers since both muscle specific and housekeeping transcripts display the same pattern.
This perinuclear clustering is an active mechanism, dependent on the minus end directed microtubule motor dynein and its activator dynactin. We have also established that the levels of protein translation can depend on nuclear location. Ribosome content is higher in the nuclear region, independently of Dynactin2 expression. Using a heterokaryon system, we show that at least some proteins in the cell remain localized close to their nucleus of origin. Moreover, contractibility of the cells correlates with the position of the nucleus and thus with overall mRNA localization.
Interestingly, a peculiar subset of mRNAs localizes regardless of where the nucleus is placed. A common feature of these transcripts is their extremely big length. We confirmed that this differential distribution is also happening in vivo. We propose that an active mechanism is responsible for this “giant” mRNA localization in order to ensure and facilitate the localization of the encoded proteins. Understanding the mechanisms of mRNA transport and anchoring that govern its subcellular destinations in myofibers may be the key to understand how nuclear positioning impacts muscle activity
Unraveling new mechanisms for nuclear positioning prior to cell migration
No full textSFRH/BD/52227/201
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