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NEW INSIGHTS INTO THE ROLE OF THE CENTROSOMAL MARK4 KINASE IN REGULATING THE DYNAMICS AND REMODELLING OF CYTOSKELETON FROM OVEREXPRESSION STUDIES OF ITS TWO ISOFORMS IN NORMAL AND TUMOR CELLS
Full text linkMAP/Microtubule Affinity Regulating Kinase 4 (MARK4) belongs to a highly conserved family of serine–threonine kinases (MARKs) that are able to phosphorylate the microtubule associated proteins (MAPs), and cause these proteins to detach from microtubules (MTs) increasing microtubules dynamics. MARKs kinases represent the mammalian homologues of PAR-1, a protein involved in establishment of the cell shape and polarity in lower eukaryotes.
The MARK4 gene is located at 19q13.2 and encodes at least two alternatively spliced isoforms, MARK4L and MARK4S, which have an identical protein structure apart from the C-terminal region. The two isoforms are differentially expressed in human tissues, particularly in the central nervous system (CNS). Several studies reported that MARK4S is expressed in normal brain tissue and neurons, suggesting that this isoform has a role in neuronal differentiation. Conversely, MARK4L is up-regulated in glioma and neural progenitor cells, pointing to a possible role of this isoform in cell proliferation. Recently, we highlighted an increasingly subverted MARK4L/MARK4S ratio, with prevalence of MARK4L, in glioblastoma and glioblastoma-derived cancer stem cells, that recapitulate the expression profiling of neural stem cells. These findings suggest that the expression of the two MARK4 isoforms is tightly regulated during the proliferation/differentiation of neural stem cells and changes in their expression levels may be a molecular marker of tumour transformation.
Unlike the other members of the family (MARK1, MARK2 and MARK3), that exhibit uniform cytoplasmic localisation, both MARK4 isoforms localise at the centrosomes and in the midbody, supporting their involvement in mitotic division and cytokinesis.
To elucidate the role played by MARK4 isoforms in cell cycle progression and in the regulation of the cytoskeleton, we monitored the activation status of MARK4 during the cell cycle and performed overexpression experiments in fibroblasts and glioma cell lines.
We showed that despite MARK4 is expressed across all the cell cycle phases, its active form, phosphorylated at the Thr214 residue, is prevalent in mitosis. Phospho-MARK4 is detected in centrosomes at all mitotic stages and in the midbody during cytokinesis. Conversely, only a fraction of interphase centrosomes show phospho-MARK4 positive signals.
Overexpression experiments on fibroblasts and glioma cell lines demonstrated the role of MARK4 in the regulation of cytoskeleton dynamics. Indeed overexpression of MARK4L or MARK4S led to a sharp decrease in microtubule density in both the cell systems, as monitored by immunofluorescence experiments. By contrast, overexpression of catalytically inactive MARK4L/MARK4S mutants, did not affect the microtubule network, indicating that the effects on MTs are dependent on the kinase activity of MARK4 and likely linked to MAPs phosphorylation.
Besides the effect on MT array, overexpressed MARK4L in fibroblasts showed a filamentous staining pattern, co-localising with vimentin, the core component of cytoskeleton intermediate filaments. In contrast, overexpressed MARK4S co-localised with vimentin to a lesser extent and only in few cells.
The MARK4L-vimentin co-localisation was particularly evident in the perinuclear zone and in some overexpressing cells, the filaments appeared reshaped as compared to those in GFP-transfected cells, and showed the formation of bundle structures. These alterations seem to be due to the kinase activity of MARK4L since overexpression of kinase dead mutants did not remodel the intermediate filaments.
The overall data highlight MARK4 as a key component in the regulation of microtubules dynamics, and indicate vimentin as a plausible target of MARK4L activity, suggesting a wide-ranging influence of MARK4 on cytoskeleton. Moreover the dynamic involvement of active MARK4 in structure like centrosomes and midbody, crucial for mitosis and cytokinesis, point to a fundamental role for this kinase in the cell cycle
First archaeobotanical analysis from a medieval well (14th century AD) in Sassari (Sardinia, Italy)
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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
Suggestive evidence on the involvement of polypyrimidine-tract binding protein in regulating alternative splicing of MAP/microtubule affinity-regulating kinase 4 in glioma
No full textMAP/microtubule affinity-regulating kinase 4 (MARK4) is a serine-threonine kinase that phosphorylates microtubule-associated proteins taking part in the regulation of microtubule dynamics. MARK4 is expressed in two spliced isoforms characterized by inclusion (MARK4S) or exclusion (MARK4L) of exon 16. The distinct expression profiles in the central nervous system and their imbalance in gliomas point to roles of MARK4L and MARK4S in cell proliferation and cell differentiation, respectively. Having ruled out mutations and transcription defects, we hypothesized that alterations in the expression of splicing factors may underlie deregulated MARK4 expression in gliomas.Bioinformatic analysis revealed four putative polypyrimidine-tract binding (PTB) protein binding sites in MARK4 introns 15 and 16. Glioma tissues and glioblastoma-derived cancer stem cells showed, compared with normal brain, significant overexpression of PTB, correlated with high MARK4L mRNA expression. Splicing minigene assays revealed a functional intronic splicing silencer in MARK4 intron 15, but mutagenesis of the PTB binding site in this region did not affect minigene splicing, suggesting that PTB may bind to a splicing silencer other than the predicted one and synergistically acting with the other predicted PTB sites. Electrophoretic mobility shift assays coupled with mass spectrometry confirmed binding of PTB to the polypyrimidine tract of intron 15, and thus its involvement in MARK4 alternative splicing. This finding, along with evidence of PTB overexpression in gliomas and glioblastoma-derived cancer stem cells and differentiated progeny, merged in pointing out the involvement of PTB in the switch to MARK4L, consistent with its established role in driving oncogenic splicing in brain tumors
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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