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REGULATORY ELEMENTS AND BIOMIMETIC SIGNALS IN NEURITOGENESIS, NEURAL DEVELOPMENT AND REGENERATIVE MEDICINE
No full textHomodimerization between Cell Adhesion Molecules (CAMs) of the immunoglobulin family play a central role in cell-cell and cell-extracellular matrix interactions. Specific Ig-like repeats from the extracellular domains of neuronal CAMs share a highly conserved Neurite Outgrowth and Guidance (NOG) motif, which is crucial in mediating such interactions during neural development and repair. Synthetic peptides derived from the NOG motif of such proteins can promote neurite sprouting and elongation in cell cultures at levels comparable to whole recombinant proteins by binding to a cleft between the second and third Ig-like domain of L1CAM. This protein is known to be crucial to neuronal differentiation in both mature and developing nervous systems. Several studies suggest that many of its functional interactions are mediated by homodimerization via Ig2 domains. X-linked mutations in the human L1CAM gene cause the L1 syndrome, a severe neurodevelopmental disorder that, in most cases, abrogates L1CAM homodimerization and neurite outgrowth in cell models. In silico simulations provided a molecular rationale for L1 syndrome phenotypes resulting from mutations I179S and R184Q in the NOG region of L1CAM. Simulations allowed the identification of a structural rationale for the severity of the phenotype. Notably, even if the dimerization interface was disrupted upon mutation, simulations proved that the peptide binding pocket on the L1CAM surface is preserved even upon R184Q mutation. Notably, while treatment with recombinant L1CAM ectodomain proved ineffective, NOG peptides could rescue neuritogenesis in a cellular model of the CRASH syndrome. Evidence presented in this thesis describes the role of the NOG motif in neuronal CAMs structure and function to using NOG-derived peptides as biotechnological and therapeutic tools.
L1CAM is transported towards the plasma membrane in a process depending on VAMP7, a member of the SNARE and longin families involved in vesicular trafficking. Splicing of VAMP7 results in a total of 7 different protein-coding isoforms. Among the minor isoforms identified so far, VAMP7j is the most expressed in the human brain. Functional and structural evidence suggests VAMP7j lacks a functional SNARE motif but retains both the longin and transmembrane domains. Evidence presented here suggests VAMP7j modulates L1CAM-dependent neurite growth by mediating the transport of L1CAM toward the plasma membrane in a mechanism requiring LRRK1 and dependent on the phosphorylation of the longin domain.
The importance of VAMP7 splicing in neuronal maturation was also considered. The Methyl CpG binding protein 2 (MeCP2) has been previously identified to bind the VAMP7 gene, suggesting MeCP2 could be relevant in modulating VAMP7 splicing. A human iPSCs line carrying the MeCP2T158M mutation and its isogenic control was differentiated into mature cortical neurons and harvested for RT-qPCR. qRT-PCR analysis of isogenic controls indicated all but one VAMP7 isoform exhibits a strong upregulation upon cortical differentiation of hiPSCs. When isogenic controls were compared with mutant cell lines, all isoforms stopped showing any modulation over time. Strikingly, VAMP7b and VAMP7j, missing exon 6 and exon 5 and 6, respectively, showed a steep decrease (up to 400%) in expression level upon mutation of MeCP2. Overall, this thesis work identified in the structural features of the NOG region and in the regulation of L1CAM trafficking mediated by VAMP7j, two elements contributing to the regulation of neurite outgrowth. Moreover, an application of NOG-derived peptides was also investigated, and a proof of concept for their use to rescue an L1-syndrome phenotype in a cell model is presented
VAMP7j: A Splice Variant of Human VAMP7 That Modulates Neurite Outgrowth by Regulating L1CAM Transport to the Plasma Membrane
Get PDFThe vesicle-associated membrane protein 7 (VAMP7) is a SNARE protein of the longin family involved in a wide range of subcellular trafficking events, including neurite sprouting and elongation. The expression of the human gene SYBL1, encoding VAMP7, is finely regulated by alternative splicing. Among the minor isoforms identified so far, VAMP7j is the one most expressed and modulated in the human brain. Therefore, we focused on gaining functional evidence on VAMP7j, which lacks a functional SNARE motif but retains both the longin and transmembrane domains. In human SH-SY5Y cells, we found VAMP7j to modulate neuritogenesis by mediating transport of L1CAM toward the plasma membrane, in a fashion regulated by phosphorylation of the longin domain. VAMP7-mediated regulation of L1CAM trafficking seems at least to differentiate humans from rats, with VAMP7j CNS expression being restricted to primates, including humans. Since L1CAM is a central player in neuritogenesis and axon guidance, these findings suggest the species-specific splicing of SYBL1 is among the fine tuners of human neurodevelopmental complexity
Exogenous Players in Mitochondria-Related CNS Disorders: Viral Pathogens and Unbalanced Microbiota in the Gut-Brain Axis
Get PDFBillions of years of co-evolution has made mitochondria central to the eukaryotic cell and organism life playing the role of cellular power plants, as indeed they are involved in most, if not all, important regulatory pathways. Neurological disorders depending on impaired mitochondrial function or homeostasis can be caused by the misregulation of “endogenous players”, such as nuclear or cytoplasmic regulators, which have been treated elsewhere. In this review, we focus on how exogenous agents, i.e., viral pathogens, or unbalanced microbiota in the gut-brain axis can also endanger mitochondrial dynamics in the central nervous system (CNS). Neurotropic viruses such as Herpes, Rabies, West-Nile, and Polioviruses seem to hijack neuronal transport networks, commandeering the proteins that mitochondria typically use to move along neurites. However, several neurological complications are also associated to infections by pandemic viruses, such as Influenza A virus and SARS-CoV-2 coronavirus, representing a relevant risk associated to seasonal flu, coronavirus disease-19 (COVID-19) and “Long-COVID”. Emerging evidence is depicting the gut microbiota as a source of signals, transmitted via sensory neurons innervating the gut, able to influence brain structure and function, including cognitive functions. Therefore, the direct connection between intestinal microbiota and mitochondrial functions might concur with the onset, progression, and severity of CNS diseases
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
Design and experimental validation of an optimized microalgae-bacteria consortium for the bioremediation of glyphosate in continuous photobioreactors
No full textGlyphosate will be banned from Europe by the end of 2022, but its widespread use in the last decades and its persistence in the environment require the development of novel remediation processes. In this work, a bacterial consortium was designed de novo with the aim to remove glyphosate from polluted water, supported by the oxygen produced by a microalgal species. To this goal, bioinformatics tools were employed to identify the bacterial strains from contaminated sources (Pseudomonas stutzeri; Comamonas odontotermitis; Sinomonas atrocyanea) able to express enzymes for glyphosate degradation, while the microalga Chlorella protothecoides was chosen for its known performances in wastewater treatment. To follow a bioaugmentation approach, the designed consortium was cultivated in continuous photobioreactors at increasing glyphosate concentrations, from 5 to 50 mg L-1, to boost its acclimation to the presence of the herbicide and its capacity to remove it from water. C. protothecoides tolerance to glyphosate was verified through batch experiments. Remarkably, steady state conditions were reached and the consortium was able to live as a community in the reactor. The consortium activity was validated in both synthetic and real wastewater, where glyphosate concentration was reduced by about 53% and 79%, respectively, without the detection of aminomethylphosphonic acid formation
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
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