1,720,969 research outputs found
Regulated interactions of the SUMO ligase RANBP2 with the mitotic spindle and kinetochores during mitotic progression
Full text linkRANBP2 is a large nucleoporin (NUP) residing at nuclear pore complexes (NPCs) in interphase and plays a role in nucleo-cytoplasmic transport of macromolecules across the NPC. In mitosis, when nuclear envelope (NE) breaks down and NPCs disassemble, RANBP2 localizes on mitotic structures. RANBP2 has SUMO (small ubiquitin-related modifier) E3 ligase and SUMO stabilizing activities and regulates protein SUMO conjugation, a post-translational modification of particular importance in dynamic processes such as the DNA damage response, stress response, various signaling pathways and mitosis. A characterized SUMOylated RANBP2 target is RANGAP1, the GTP-hydrolysis activating factor for theGTPase RAN. RANBP2 and RANGAP1, together with Ubc9 (a SUMO E2 enzyme), form a complex, called RRSU (RANBP2/RANGAP1-SUMO/UBC9), that has enhanced SUMO ligase activity and localizes to kinetochores (KTs) in metaphase with a mechanism that is not completely understood.
The goal of my PhD project was to identify the molecular mechanisms regulating the RRSU complex localization in space and time during mitosis, particularly to KTs, given the importance of these structures as the connecting structures between chromosomes and the mitotic spindle and their crucial role in chromosome segregation.
Both RANBP2 and RANGAP1 are known to interact with nuclear transport receptors, Importin beta and CRM1, during nuclear transport in interphase. In my project I have developed in situ proximity ligation assays (PLA) to visualize their interactions with these transport factors, follow their dynamics during cell division and assess whether nuclear transport receptors have themselves a functional role in the RSSU complex localization in mitotic cells.
PLA results show that the RRSU complex engages in dynamic interactions with Importin beta and CRM1 during mitotic progression: it preferentially interacts with Importin beta in early mitotic stages along the spindle MTs. In metaphase, after MTs attach all KTs, this interaction decreases. Concomitantly, the RRSU complex also interacts with CRM1: this interaction becomes up-regulated in metaphase and becomes visible at MT attached-KTs. Thus, the RRSU complex appears to “switch partners” from prometaphase (prevalent engagement with Importin beta along the spindle) to metaphase (increased PLA signals with CRM1 at KTs), suggesting that protein SUMO conjugation takes place with a spatially and temporally regulated programme in mitosis.
To validate the “switch partner” model I generated inducible cell lines, both for Importin beta and CRM1, to assess whether unbalancing one or the other would influence the RRSU complex localization in mitosis. Results from experiments with the inducible cell lines show that the mitotic localization of the RRSU complex depends on the antagonistic actions of Importin beta and CRM1: indeed, unbalancing each one of them impairs the RSSU complex localization and concomitantly generates segregation defects, suggesting that KT functions are defective. Overall, the results of my project highlight the importance of localized SUMOylation of proteins at the mitotic apparatus and KTs for balanced chromosome segregation, and indicate a role of nuclear transport receptors as upstream regulators in the process. It is of note that several cancer types overexpress these transport factors, which may contribute to the high level of genetic instability observed in these cancers
Signaling from internalized receptors
No full textActivation of many receptors triggers a cascade of signal transducing events and increases their rate of internalization. Receptor endocytosis has always been viewed primarily as a mechanism to negatively regulate receptor activation, but recent evidence suggests that internalization may result in the formation of specialized signaling platforms on intracellular vesicles. Thus, the investigation of the molecular composition of the various vesicular compartments, their interplay and their spatial and temporal regulation is crucial in order to fully understand the modality of cell signaling
Endocytosis and Cancer : an 'Insider' Network with Dangerous Liaisons
No full textFrom the signaling point of view, endocytosis has long been regarded as a major mechanism of attenuation, through the degradation of signaling receptors and, in some cases, of their ligands. This outlook has changed, over the past decade, as it has become clear that signaling persists in the endocytic route, and that intracellular endocytic stations (the 'signaling endosomes') actually contribute to the sorting of signals in space and time. Endocytosis-mediated recycling of receptors and of signaling molecules to specific regions of the plasma membrane is also coming into focus as a major mechanism in the execution of spatially restricted functions, such as cell motility. In addition, emerging evidence connects endocytosis as a whole, or individual endocytic proteins, to complex cellular programs, such as the control of the cell cycle, mitosis, apoptosis and cell fate determination. Thus, endocytosis seems to be deeply ingrained into the cell regulation blueprint and its subversion is predicted to play an important role in human diseases: first and foremost, cancer
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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