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Ca2+-binding to the C2E domain of otoferlin is required for hair cell exocytosis and hearing
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Biochemical Characterization of Otoferlin, the Ca2+ sensor for exocytosis at inner hair cell synapses
No full textTransmission of sound from the ear to the brain requires high temporal and spatial fidelity. Inner hair cells (IHC) of the inner ear are the primary sensory organ of hearing, forming the first synapse of the auditory pathway. Depolarization of IHCs by incoming sound vibrations causes Ca2+ triggered fusion of glutamate filled synaptic vesicles (SVs) with the plasma membrane. SV fusion at the IHC synapse operates with micro-second level precision and needs to be sustained over prolonged time periods.
Rates of SV fusion at IHC synapses are orders of magnitude higher than central nervous system (CNS) synapses. The synaptic machinery of IHC synapses contributes to maintaining indefatigable release and differs from that of CNS synapses. The IHC synapse is characterized by the presence of an electron dense ultrastructure termed the ribbon. The ribbon acts as a super scaffold, tethering SVs at the AZ, replenishing the releasable pool of SVs and coupling Ca2+ channels to the AZ. Many proteins required for SV fusion at CNS synapses- SNAREs, Syt-1, Munc13, Munc18, complexins- are either absent or expendable for exocytosis at IHC synapses.
Otoferlin (Otof) a multi C¬2 domain protein primarily expressed in IHCs has been identified to be essential for hearing, with mutations in the gene encoding the protein causing hearing impairment. Otof KO mice were found to be profoundly deaf, and Ca2+ triggered exocytosis was completely abolished in Otof-/- IHCs. Physiological analysis of point mutations indicated roles for Otof in vesicle tethering, release, replenishment and endocytosis at the IHC synapse. Biochemical analysis of individual C2 domains of the protein indicated that the domains bind neuronal t-SNAREs and anionic lipid membranes in a Ca2+ dependent manner. These insights have laid the basis for Otof as a putative Ca2+ sensor for exocytosis at IHC synapses.
However, a thorough mechanistic understating of the protein is lacking. This is due to a dearth of in vitro data characterizing the full length protein. The bottleneck has been the difficulty in purifying the full length protein, hence in vitro work has been limited to truncation constructs. In this work a robust and reproducible protocol for purifying full length Otof, along with constructs lacking the TMD and C2A domain has been developed. We have also characterized the protein with respect to its Ca2+ binding, lipid binding and membrane bridging properties. Furthermore, employing bulk lipid mixing assays, the role of Otof in SNARE dependent and independent membrane fusion was probed.
Otof was found to enhance SNARE mediated membrane fusion in a Ca2+ dependent manner, supporting its role as a Ca2+ sensor for exocytosis. The protein was also found to interact with the neuronal SNAREs. Enhancement of fusion by Otof was dependent on the presence of anionic lipids (PS and PiP2). Our data also show that Otof can tether and dock vesicles at discrete distances and that this function relies strongly on the presence of anionic lipids (PS and PiP2). Based on this work, we propose a model for the function of Otof at the IHC synapse.2025-09-2
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Get PDFWe 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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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