1,721,152 research outputs found
N-Cadherin adhesive ligation regulates mechanosensitive neural stem cell lineage commitment in 3D matrices
No full textDuring differentiation, neural stem cells (NSCs) encounter diverse cues from their niche, including not only biophysical cues from the extracellular matrix (ECM) but also cell-cell communication. However, it is still poorly understood how these cues cumulatively regulate mechanosensitive NSC fate commitment, especially in 3D matrices that better mimic in vivo systems. Here, we develop a click chemistry-based 3D hydrogel material system to fully decouple cell-cell and cell-ECM interactions by functionalizing small peptides: the HAVDI motif from N-cadherin and RGD motif from fibronectin. The hydrogel is engineered to range in stiffness from 75 Pa to 600 Pa. Interestingly, HAVDI-mediated interaction shows increased neurogenesis, except for the softest gel (75 Pa). Moreover, the HAVDI ligation attenuates the mechanosensing state of NSCs, exhibiting restricted cytoskeletal formation and RhoA signaling. Given that mechanosensitive neurogenesis has been reported to be regulated by cytoskeletal formation, our finding suggests that the enhanced neurogenesis in the HAVDI-modified gel may be highly associated with the HAVDI interaction-mediated attenuation of mechanosensing. Furthermore, NSCs in the HAVDI gel shows higher beta-catenin activity, which has been known to promote neurogenesis. Our findings provide critical insights into how mechanosensitive NSC fate commitment is regulated as a consequence of diverse interactions in 3D microenvironments.
N-cadherin adhesive interaction of human neural stem cells affects the mechanosensitive fate commitment in a three-dimensional environment
No full textSpectrin mediates 3D-specific matrix stress-relaxation response in neural stem cell lineage commitment.
Full text linkWhile extracellular matrix (ECM) stress relaxation is increasingly appreciated to regulate stem cell fate commitment and other behaviors, much remains unknown about how cells process stress-relaxation cues in tissue-like three-dimensional (3D) geometries versus traditional 2D cell culture. Here, we develop an oligonucleotide-crosslinked hyaluronic acid-based ECM platform with tunable stress relaxation properties capable of use in either 2D or 3D. Strikingly, stress relaxation favors neural stem cell (NSC) neurogenesis in 3D but suppresses it in 2D. RNA sequencing and functional studies implicate the membrane-associated protein spectrin as a key 3D-specific transducer of stress-relaxation cues. Confining stress drives spectrins recruitment to the F-actin cytoskeleton, where it mechanically reinforces the cortex and potentiates mechanotransductive signaling. Increased spectrin expression is also accompanied by increased expression of the transcription factor EGR1, which we previously showed mediates NSC stiffness-dependent lineage commitment in 3D. Our work highlights spectrin as an important molecular sensor and transducer of 3D stress-relaxation cues
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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Directed Evolution of Novel Adeno-Associated Viruses for Therapeutic Gene Delivery
Full text linkGene delivery vehicles, or vectors, based on adeno-associated viruses (AAV) have demonstrated success in both preclinical disease models and recently in human clinical trials for several disease targets, including muscular dystrophy, hemophilia, Parkinson's disease, Leber's congenital amaurosis, and macular degeneration. AAV gene therapy vectors have become increasingly utilized because the parent virus is nonpathogenic in humans, they can transduce both dividing and non-dividing cells, and they are efficient for some important cell and tissue types. AAV's simple genome contains two open reading frames, which encode the nonstructural proteins needed for viral replication and virus assembly (rep) and the three structural proteins that assemble to form a 60-mer viral capsid (cap). To create a gene therapy vector, a therapeutic gene of interest is inserted in place of the viral open reading frames to be packaged during vector production. Despite its considerable promise and emerging clinical success, several challenges impede the broader implementation of AAV gene therapy, including the prevalence of anti-AAV neutralizing antibodies in the human population due to natural exposure to the parent virus, low transduction of a number of therapeutically relevant cell types, and an inability to overcome physical transport barriers in the body. These challenges arise since the demands we place on AAV vectors are often different from or even at odds with the properties nature bestowed on their parent viruses. Viral directed evolution - the iterative generation of large, diverse libraries of viral mutants and selection for variants with specific properties of interest - offers a promising means to address these problems.Directed evolution is a high-throughput, molecular engineering approach that our group has adapted and implemented to create AAV variants with novel properties, such as altered receptor binding, altered cell transduction, and altered tissue transduction in the body. In general, the method emulates the process of natural evolution, in which repeated genetic diversification and selection enable the accumulation of key mutations or genetic modifications that progressively improve a molecule's function, even without knowledge of the underlying mechanistic basis for the problem. For AAV, this process has involved mutating wild-type AAV cap genes to create large genetic libraries, which can be packaged to generate libraries of viral particles, each of which is composed of a variant capsid surrounding a viral genome encoding that capsid. A selective pressure - such as high-affinity antibodies against the AAV capsid, the ability to infect adult neural stem cells, or the ability to infect human pluripotent stem cells - is then applied to promote the emergence of variants able to surmount these barriers. After each such selection step, the successful variants can be recovered and used as the starting material for the next selection step to further enrich for improved variants. After several such selection steps, the resulting cap gene pool is subjected to additional mutagenesis and selection. After several rounds of mutagenesis and selection, the resulting variants can be analyzed individually for the desired property.Using directed evolution, I have engineered several novel AAV variants capable of enhanced gene delivery in several applications. First, variants selected in the presence of pooled human antibodies were 2- to 35-fold less susceptible to neutralization by anti-AAV antibodies compared to parental AAV in vitro. The antibody neutralization properties also translated to enhanced transduction in an in vivo mouse model in the presence of neutralizing antibodies. The isolation of such novel variants resistant to anti-AAV antibodies may enable the future treatment of patients with pre-existing immunity that are currently ineligible for AAV gene therapy. Second, a novel variant selected for the ability to infect adult neural stem cells was capable of more efficient gene delivery to rat, mouse, and human neural stem cells in vitro. Furthermore, the variant demonstrated more efficient and specific transduction of rat and mouse neural stem cells in vivo compared to natural AAV serotypes. Gene delivery to neural stem cells using this variant could be used as a gene therapy option to better harness these cells for tissue regeneration. Finally, a novel variant selected for the ability to infect human pluripotent stem cells was able to transduce several human embryonic stem cell and induced pluripotent stem cell lines 3-fold more efficiently than natural AAV serotypes, which enabled a 10-fold increase in the efficiency of a genome-editing technique termed gene targeting. These results demonstrate that engineered and evolved AAV vectors are highly promising for a range of applications from the lab to the clinic
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