Biology subjects

Samaddar, S.

Publications and source records attributed to Samaddar, S..

17 recordsLinked to original sources

bioRxiv2026

FTO-Dependent m6A RNA Dysregulation Underlies Memory Deficits Induced by Early-Life Stress

Cognitive functions in adults are mainly attributed to experience-dependent plasticity. Nonetheless, the developmental encoding of memory deficits is still inadequately addressed. Here, we demonstrate that early-life stress (ELS) reprograms the hippocampal epitranscriptome by enhancing N6-methyladenosine (m6A) deposits during early development leading to memory deficit in adulthood. We observed a shift toward hypermethylation of transcripts including coding and non-coding RNAs (lncRNAs) following maternal separation. We also observed that these transcripts encoding proteins necessary for translational regulation, ribosome biogenesis and mitochondrial function. This epitranscriptomic change is driven by ELS-induced downregulation of the m6A demethylase FTO (Fat mass and obesity-associated protein). We observe that the overexpression of FTO in young adult mice selectively rescues memory deficits without ameliorating elevated anxiety. Further, the knockdown of FTO in primary hippocampal neuron, mimicking ELS - induced reduction of its expression, leads to reduced translation as detected by puromycin labelling. Taken together, our study demonstrated previously uncharacterized mechanism of ELS-induced epitranscriptomic change linked with memory deficit via the regulation of protein synthesis.

neuroscience↗

bioRxiv2026

Machine Learning Ensemble Reveals Distinct Molecular Pathways of Retinal Damage in Spaceflown Mice

BackgroundSpaceflight-associated neuro-ocular syndrome (SANS) poses significant risks to astronaut visual health during long-duration missions, yet its underlying molecular mechanisms remain incompletely understood. Oxidative stress and apoptosis are candidate molecular drivers, but their transcriptomic signatures in spaceflight-exposed retinal tissue have not been systematically characterized. MethodsWe applied a machine learning ensemble of linear regression models to predict two ocular phenotypes: 4-hydroxynonenal (4-HNE) immunostaining as a marker of lipid peroxidation-mediated oxidative damage; and TUNEL positivity as a marker of apoptotic cell death. In this observational study, we use bulk retinal gene expression data obtained from a controlled experiment with ground control and spaceflown mice to predict these phenotypes. Gene Ontology pathway enrichment was performed on the most predictive gene sets for each phenotype. ResultsThe 4-HNE phenotype was predicted by genes that converge on membrane-associated pathways, photoreceptor protein modification, synaptic dysfunction, and extracellular matrix dysregulation, including B2m, Tf, Cnga1, mt-Nd1, Snap25, and Efemp1. The genes predicting the TUNEL phenotype revealed a distinct signature emphasizing stress-induced apoptosis, rod photoreceptor degeneration, and endoplasmic reticulum dysfunction, with Ddit4, Nrl, Rom1, Reep6, and Gabarapl1 emerging as central regulators. ConclusionsOxidative lipid peroxidation and apoptotic cell death represent complementary and molecularly distinct pathological mechanisms in spaceflight-exposed murine retinal tissue. The gene signatures provide a putative molecular framework for developing noninvasive biomarkers and therapeutic targets to monitor and protect astronaut visual health during long-duration and deep-space missions.

bioinformatics↗

bioRxiv2024

The RNA binding ubiquitination ligase MEX3B regulates bFGF-dependent neuronal proliferation.

BackgroundE3 ubiquitin ligases, integral components of the proteasomal degradation cascade, are critical for regulating the cellular proteome via canonical proteasome-mediated protein degradation; however, the non-canonical functions of these ligases in neuronal development are poorly understood. Our study focuses on a special class of E3 ubiquitin ligases known as RNA Binding Ubiquitin Ligases (RBUL) that harbour RNA-binding domains; allowing them to acquire all the properties of RNA-binding proteins (RBPs) and regulate transcriptional or post-transcriptional changes associated with the control of gene expression in cellular phenotypes. We aim to identify one such RUBL in the context of the highly dynamic yet stringently controlled process of neural proliferation and neural fate determination. ResultsMEX3B protein is a member of the MEX3 family and a part of the RBUL class of E3 ligases. It is differentially expressed in Neural Progenitor Cells (NPCs) upon differentiation. Mex3b RNA and protein were found to have temporally opposing expression patterns in presence of basic fibroblast growth factor (bFGF), a key signalling protein involved in neuronal proliferation. MEX3B is required for maintenance of the proliferative state of NPCs, whereas, its knockdown promotes transition from proliferative to differentiation state even in presence of bFGF that restricts differentiation. Furthermore, the knockdown of MEX3B protein results in the appearance of morphological hallmarks associated with early stages of neuronal differentiation including increase in neurite length and complexity. MEX3B interacts with the pro-proliferative transcription activator REST and the long non-coding RNA, HOTAIR. The study suggests the existence of a bFGF-dependent, combinatorial axis involving Mex3b, REST and HOTAIR, for the maintenance of NPC proliferative states. ConclusionMEX3B, containing RNA binding motifs, is a unique E3 ligase that is necessary for bFGF-dependent proliferation. Mex3b protein invokes its non-canonical function of an RNA binding protein to form a tripartite complex with the transcription activator REST and HOTAIR lncRNA to define the proliferative state of NPCs. The study highlights a unique feature of special E3 ligases in neuronal proliferation during brain development that was previously overlooked.

neuroscience↗

bioRxiv2024

Reduced accrual of mineral-associated organic matter after two years of enhanced rock weathering in cropland soils, though no net losses of soil organic carbon

Enhanced rock weathering (ERW), the application of crushed silicate rock to soil, can remove atmospheric carbon dioxide by converting it to (bi)carbonate ions or solid carbonate minerals. However, few field studies have empirically evaluated ERW in field settings. A critical question remains as to whether additions of crushed rock might positively or negatively affect soil organic matter (SOM) - Earths largest terrestrial organic carbon (C) pool and a massive reservoir of organic nitrogen (N). Here, in three irrigated cropland sites in California, USA, we investigated the effect of crushed meta-basalt rock additions on different pools of soil organic carbon and nitrogen (i.e., mineral-associated organic matter and particulate organic matter), active microbial biomass, and microbial community composition. After two years of crushed rock additions, mineral-associated organic matter (MAOM) stocks were lower in the upper surface soil (0-10 cm) compared to unamended controls. At the two sites where baseline pre-treatment data were available, neither total SOC nor SON decreased over the two years of study in crushed rock or unamended control plots. However, the accrual rate of MAOM-C and MAOM-N at 0-10 cm was lower in plots with crushed rock vs. unamended controls. Before ERW is deployed at large scales, our results suggest that field trials should assess the effects of crushed rock on SOM pools, especially over multi-year time scales, to accurately assess changes in net C and understand the mechanisms driving interactions between ERW and SOM cycling.

ecology↗

bioRxiv2023

Diet-induced miRNAs regulate adult neurogenesis and functional activity of nascent neurons in the hypothalamus

A high-fat diet (HFD) regulates the feeding circuitry in young-adult mice by stimulating neurogenesis from {beta}2 tanycytes in the hypothalamus. However, the fate of HFD-induced tanycytic neurogenesis, the functional attributes of the nascent neurons, and mechanisms underlying their subsequent integration into the feeding-related neural circuitry remain unclear. microRNAs (miRNAs) are known to play crucial roles in adult neurogenesis. In this study, miRNA profiling of BrdU-labelled neurogenic {beta}2 tanycytes from HFD-fed mice identified a cohort of miRNAs that originate from different chromosomal loci rather than a single genomic cluster. Network analysis of predicted targets for these HFD-induced miRNAs identified key "hub" mRNA targets that influence neurogenesis and the functional integration of newborn neurons. These HFD-induced miRNAs promoted the differentiation of nascent neurons into orexigenic AgRP+ and anorexigenic POMC+ neurons. Interestingly, only AgRP+ newborn neurons were selectively integrated into the functional feeding circuit, as detected by c-Fos immunostaining. This integration was disrupted when HFD-induced miRNA activity was suppressed via hypothalamic miRNA sponge expression. Furthermore, HFD feeding increased body weight in female mice, which was abrogated upon the inhibition of HFD-induced miRNAs. Magnetic resonance imaging (MRI) revealed elevated liver fat in HFD-fed mice, which reverted to normal levels when the HFD-induced miRNAs in hypothalamic tanycytes were blocked. Collectively, the findings from our study highlight a miRNA-mediated paradigm that links HFD-induced neurogenesis from {beta}2 tanycytes to weight gain and liver fat accumulation, and identifies the selective integration of AgRP+ neurons into the feeding circuitry as a possible causality of HFD-induced changes to body weight. Significance StatementThis study highlights a miRNA-network that biases the transcriptional program in hypothalamic tanycytes to promote neurogenesis in young adult mice following their exposure to an acute high-fat diet (HFD) paradigm. These HFD-induced miRNAs have the potential to alter the brains feeding circuitry by promoting neurogenesis and the preferential functional integration of nascent orexigenic (AgRP+) neurons; resulting in weight gain and hepatic fat accumulation. Collective inhibition of this miRNA-network prevents the integration of newborn AgRP+ neurons and reverses the metabolic consequences of high-fat diet. Our study provides an unexplored link between diet, neurogenesis, and remodeling of the feeding circuitry; and reveals potential therapeutic targets for combating hyperphagic obesity.

neuroscience↗

bioRxiv2023

Tick extracellular vesicles impair epidermal homeostasis through immune-epithelial networks during hematophagy

Wound healing has been extensively studied through the lens of inflammatory disorders and cancer, but limited attention has been given to hematophagy and arthropod-borne diseases. Hematophagous ectoparasites, including ticks, subvert the wound healing response to maintain prolonged attachment and facilitate blood-feeding. Here, we unveil a strategy by which extracellular vesicles (EVs) ensure blood-feeding and arthropod survival in three medically relevant tick species. Through single cell RNA sequencing and murine genetics, we demonstrate that wildtype animals infested with EV-deficient Ixodes scapularis display a unique epidermal sub-population with a mesenchymal-like transcriptional program and an overrepresentation of pathways connected to wound healing. Furthermore, tick EVs inhibit proliferation and diminish the capacity of wound closure in keratinocytes. This occurrence was linked to phosphoinositide 3-kinase activity, keratinocyte growth factor 1 (KGF-1) and transforming growth factor {beta} (TGF-{beta}) levels. Collectively, we uncovered a strategy employed by a blood-feeding arthropod that disrupts the circuitry in cutaneous wound healing, contributing to ectoparasite fitness.

microbiology↗

bioRxiv2023

Genetic manipulation of an Ixodes scapularis cell line

Although genetic manipulation is one of the hallmarks in model organisms, its applicability to non-model species has remained difficult due to our limited understanding of their fundamental biology. For instance, manipulation of a cell line originated from the blacklegged tick Ixodes scapularis, an arthropod that serves as a vector of several human pathogens, has yet to be established. Here, we demonstrate the successful genetic modification of the commonly used tick ISE6 line through ectopic expression and clustered regularly interspaced palindromic repeats (CRISPR)/CRISPR-associated protein 9 (Cas9) genome editing. We performed ectopic expression using nucleofection and attained CRISPR-Cas9 editing via homology dependent recombination. Targeting the E3 ubiquitin ligase X-linked inhibitor of apoptosis (xiap) and its substrate p47 led to alteration in molecular signaling within the immune deficiency (IMD) network and increased infection of the rickettsial agent Anaplasma phagocytophilum in I. scapularis ISE6 cells. Collectively, our findings complement techniques for genetic engineering of ticks in vivo and aid in circumventing the long-life cycle of I. scapularis, of which limits efficient and scalable molecular genetic screens. ImportanceGenetic engineering in arachnids has lagged compared to insects, largely because of substantial differences in their biology. This study unveils the implementation of ectopic expression and CRISPR-Cas9 gene editing in a tick cell line. We introduced fluorescently tagged proteins in ISE6 cells and edited its genome via homology dependent recombination. We ablated the expression of xiap and p47, two signaling molecules present in the immune deficiency (IMD) pathway of I. scapularis. Impairment of the tick IMD pathway, an analogous network of the tumor necrosis factor receptor in mammals, led to enhanced infection of the rickettsial agent A. phagocytophilum. Altogether, our findings provide a critical technical resource to the scientific community to enable a deeper understanding of biological circuits in the blacklegged tick Ixodes scapularis.

genetics↗

bioRxiv2023

Tick hemocytes have pleiotropic roles in microbial infection and arthropod fitness

Uncovering the complexity of systems in non-model organisms is critical for understanding arthropod immunology. Prior efforts have mostly focused on Dipteran insects, which only account for a subset of existing arthropod species in nature. Here, we describe immune cells or hemocytes from the clinically relevant tick Ixodes scapularis using bulk and single cell RNA sequencing combined with depletion via clodronate liposomes, RNA interference, Clustered Regularly Interspaced Short Palindromic Repeats activation (CRISPRa) and RNA-fluorescence in situ hybridization (FISH). We observe molecular alterations in hemocytes upon tick infestation of mammals and infection with either the Lyme disease spirochete Borrelia burgdorferi or the rickettsial agent Anaplasma phagocytophilum. We predict distinct hemocyte lineages and reveal clusters exhibiting defined signatures for immunity, metabolism, and proliferation during hematophagy. Furthermore, we perform a mechanistic characterization of two I. scapularis hemocyte markers: hemocytin and astakine. Depletion of phagocytic hemocytes affects hemocytin and astakine levels, which impacts blood feeding and molting behavior of ticks. Hemocytin specifically affects the c-Jun N-terminal kinase (JNK) signaling pathway, whereas astakine alters hemocyte proliferation in I. scapularis. Altogether, we uncover the heterogeneity and pleiotropic roles of hemocytes in ticks and provide a valuable resource for comparative biology in arthropods.

immunology↗

bioRxiv2023

Transcriptomic analysis identifies synapse-enriched lncRNAs required for glutamatergic synapse development and fear memory consolidation.

Regulatory functions of lncRNAs in neurons have been majorly limited to the nucleus. The identity of synaptic lncRNAs and their functional roles associated with synapse development and plasticity are poorly understood. Transcriptomic analysis from synaptoneurosomes identified 94 synapse-enriched lncRNAs from the mouse hippocampus. We find Pvt1 to be a specific regulator of excitatory, not inhibitory, synapse development. Synapse-specific loss of Pvt1 regulates synaptic activity and the downregulation of mRNAs pertinent to synapse development. We also report a synapse-centric role for an uncharacterized lncRNA; 2410006H16Rik (SynLAMP); in translation and memory formation. SynLAMP demonstrates enhanced localization to the synapse following fear conditioning and regulates dendritic translation by sequestering the translation repressor FUS; acting as a molecular decoy. Synapse-specific knockdown of SynLAMP inhibits the localised, activity-dependent translation of CamK2a, a FUS target. SynLAMP RNAi occludes fear-memory formation. Comprehensively, our study highlights that de novo activity of lncRNAs are involved in diverse synaptic functions.

neuroscience↗

bioRxiv2023

Metabolic disruption impacts tick fitness and microbial relationships

Arthropod-borne microbes rely on the metabolic state of a host to cycle between evolutionarily distant species. For instance, arthropod tolerance to infection may be due to redistribution of metabolic resources, often leading to microbial transmission to mammals. Conversely, metabolic alterations aids in pathogen elimination in humans, who do not ordinarily harbor arthropod-borne microbes. To ascertain the effect of metabolism on interspecies relationships, we engineered a system to evaluate glycolysis and oxidative phosphorylation in the tick Ixodes scapularis. Using a metabolic flux assay, we determined that the rickettsial bacterium Anaplasma phagocytophilum and the Lyme disease spirochete Borrelia burgdorferi, which are transstadially transmitted in nature, induced glycolysis in ticks. On the other hand, the endosymbiont Rickettsia buchneri, which is transovarially maintained, had a minimal effect on I. scapularis bioenergetics. Importantly, the metabolite {beta}-aminoisobutyric acid (BAIBA) was elevated during A. phagocytophilum infection of tick cells following an unbiased metabolomics approach. Thus, we manipulated the expression of genes associated with the catabolism and anabolism of BAIBA in I. scapularis and detected impaired feeding on mammals, reduced bacterial acquisition, and decreased tick survival. Collectively, we reveal the importance of metabolism for tick-microbe relationships and unveil a valuable metabolite for I. scapularis fitness.

microbiology↗

bioRxiv2023

CRISPR based programmable RNA editing in primary neurons

Investigating the RNA regulation landscape primarily relies on our understanding of how RNA-protein interactions are governed in various cell types, including neurons. Analysis of RNA-protein interactions in physiological environments warrants the development of new tools that rely on RNA manipulation. Recently, A CRISPR-based RNA-editing tool (dCas13b-ADAR2DD) was developed to mitigate disease associated point mutations in cell lines. Here, we have explored the targeted sequence editing potential of the tool (dCas13b-ADAR2DD system) by adapting it to manipulate RNA function with an aim to visualize RNA editing in primary hippocampal neurons. This is a two-component system that includes a programmable guide RNA (gRNA) complementary to the target RNA, and a catalytically dead version of the Cas13b enzyme fused to ADAR. The RNA editing protocol outlined in this manuscript relies on using the gRNA-dependent targeting of dCas13b-ADAR fusion protein to the mutant form of mDendra transcript. We first abrogated the fluorescence of Dendra2 by introducing a nonsense mutation that precludes the formation of the functional protein. To visualize the efficacy of the RNA editing in neurons, we used the dCas13b-ADAR2DD system to edit specific nucleotides within the Dendra2 mRNA to restore the amino acid codes critical for Dendra2 fluorescence. This method therefore lays the foundation to future studies on the dynamicity of activity-induced RNA-protein interactions in neurons and can be extended to manipulate the endogenous RNome in diverse neuronal subtypes. Furthermore, this methodology will enable investigators to visualize the spatial and temporal resolution of RNA-protein interactions without altering the genomes via conventional methods. HighlightsO_LICRISPR-Cas13 based application that enables site specific A-to-I in target RNAs directed by gRNA; optimized in neurons. C_LIO_LIEnables the temporal mapping of developmentally relevant RNAs and their cis-interacting RNA binding proteins. C_LI

neuroscience↗

bioRxiv2022

Post-translational modification by the Pgf glycosylation machinery modulates Streptococcus mutans physiology and virulence

Streptococcus mutans is a keystone pathogen of dental caries, and the ability to form biofilms is essential for its pathogenicity. We identified a glycosylation machinery (Pgf) in S. mutans that post-translationally modifies two surface-associated adhesins, Cnm and WapA. The four pgf genes (pgfS, pgfM1, pgfE, and pgfM2) are part of S. mutans core genome and we hypothesized that the scope of Pgf goes beyond Cnm and WapA. By inactivating each pgf gene individually or creating a quadruple pgf mutant in S. mutans OMZ175, we showed that the Pgf machinery is important for biofilm formation. Compared to OMZ175, differences in surface charge, membrane stability, and genetic competence were also observed for most mutants. Importantly, in silico analyses and tunicamycin MIC assays suggest a functional redundancy between the Pgf machinery and the rhamnose-glucose polysaccharide synthesis pathway. Using a rat oral colonization model, we showed a 10-fold reduction in recovered CFUs for the pgf quadruple mutant compared to OMZ175. Finally, using Cnm as a model, we showed by glycoproteomics analyses that Cnm is heavily modified with N-acetyl hexosamine in OMZ175 whereas phosphorylations were observed for the pgfS mutant. Our findings indicate that the Pgf machinery participates in important aspects of S. mutans pathobiology. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=164 SRC="FIGDIR/small/511621v1_ufig1.gif" ALT="Figure 1"> View larger version (53K): org.highwire.dtl.DTLVardef@146f37eorg.highwire.dtl.DTLVardef@11c0e45org.highwire.dtl.DTLVardef@ece1eaorg.highwire.dtl.DTLVardef@1e3f221_HPS_FORMAT_FIGEXP M_FIG C_FIG Abbreviated summaryIn this study, we demonstrate that the Pgf glycosylation machinery of Streptococcus mutans, a keystone pathogen of dental caries, regulates several aspects of bacterial pathophysiology that ultimately contribute to S. mutans fitness in oral colonization experiments. Using the heavily glycosylated Cnm adhesin as a model, we found that inactivation of the glycosyltransferase PgfS results in loss of Cnm glycosylation, but instead, Cnm became heavily phosphorylated, suggesting a crosstalk/competition between these two post-translational modification mechanisms.

microbiology↗

bioRxiv2022

Musleblind-1 regulates microtubule cytoskeleton in C. elegans mechanosensory neuron through tubulin mRNAs

Regulation of microtubule cytoskeleton is fundamental for the development and maintenance of neuronal architecture. Recent studies have shown that regulated RNA processing is also critical for the establishment and maintenance of neural circuits. In a genetic screen using mechanosensory neurons of C. elegans, we identified a mutation in muscleblind-1 as a suppressor of loss of kinesin-13 family microtubule destabilizing factor klp-7. Muscleblind-1(MBL-1) is an RNA-binding protein that regulates the splicing, localization, and stability of RNA. We found that mbl-1 is required cell-autonomously for axon growth and synapse formation in the posterior lateral microtubule (PLM) neuron. Loss of mbl-1 affects stability and plus-end-out organization of microtubules in the anterior process of PLM. These defects are also accompanied by abnormal axonal transport of the synaptic protein RAB-3 and loss of gentle touch sensation in mbl-1 mutant. Our data showed that mbl-1 is genetically epistatic to mec-7 ({beta} tubulin) and mec-12 (a tubulin) for axon growth. The immunoprecipitation of MBL-1 pulls down the mec-7, mec-12, and sad-1 mRNAs. Additionally, the mbl-1 mutants show a reduction in the level and stability of mec-7 and mec-12 transcripts. Independently, mbl-1 is epistatic to sad-1 for synapse formation. Our work elucidated a previously unknown link between RNA binding protein and cytoskeletal machinery for the development and maintenance of the nervous system.

neuroscience↗

bioRxiv2022

CD36 homologs determine microbial resistance to the Lyme disease spirochete

Pattern recognition receptors sense pathogens in arthropods and mammals through distinct immune processes. Whether these molecules share a similar function and recognize the same microbe in evolutionarily distant species remain ill-defined. Here, we establish that the CD36 superfamily is required for Borrelia burgdorferi resistance in both the arthropod vector and humans. Using the blacklegged tick Ixodes scapularis and an electronic health record-linked biobank, we demonstrate that CD36 members elicit immunity to the Lyme disease spirochete. In ticks, the CD36-like protein Croquemort recognizes lipids and initiates the immune deficiency and jun N-terminal kinase pathways against B. burgdorferi. In humans, exome sequencing and clinical information reveal that individuals with CD36 loss-of-function variants have increased prevalence of Lyme disease. Altogether, we discovered a conserved mechanism of anti-bacterial immunity. One Sentence SummaryLipid receptors belonging to the CD36 superfamily exhibit a shared immune function in both ticks and humans.

immunology↗

bioRxiv2021

Amyloid aggregation of Streptococcus mutans Cnm influences its collagen-binding activity

The glycosylated collagen- and laminin-binding surface adhesin Cnm is present in approximately 20% of S. mutans clinical isolates and is associated with systemic infections and increased caries risk. Other surface-associated collagen-binding proteins of S. mutans such as P1 and WapA have been demonstrated to form an amyloid quaternary structure with functional implications within biofilms. In silico analysis predicted that the {beta}-sheet rich N-terminal collagen-binding domain (CBD) of Cnm has propensity for amyloid aggregation, whereas the threonine-rich C-terminal domain was predicted to be disorganized. In this study, thioflavin-T fluorescence and electron microscopy were used to show that Cnm forms amyloids either in its native glycosylated or recombinant non-glycosylated forms and that the CBD of Cnm is the main amyloidogenic unit of Cnm. We then performed a series of in vitro, ex vivo and in vivo assays to characterize the amylogenic properties of Cnm. In addition, Congo red birefringence indicated that Cnm is a major amyloidogenic protein of S. mutans biofilms. Competitive binding assays using collagen-coated microtiter plates and dental roots, a substrate rich in collagen, revealed that Cnm monomers inhibit S. mutans binding to collagenous substrates whereas Cnm amyloid aggregates lose this property. Thus, while Cnm contributes to recognition and initial binding of S. mutans to collagen-rich surfaces, Cnm amyloid aggregation appears to represent a mechanism to modulate this activity in mature biofilms. IMPORTANCEStreptococcus mutans is a keystone pathogen that promotes caries by acidifying the dental biofilm milieu. The collagen- and laminin-binding glycoprotein Cnm is a virulence factor found in about 20% of the clinical isolates of S. mutans. Expression of Cnm by S. mutans is associated with niche expansion, allowing colonization of multiple sites in the body including collagen-rich surfaces such as dentin and heart valves. Here, we demonstrate for the first time that Cnm function appears to be modulated by its aggregation status. As a monomer, its primary function is to promote attachment to collagenous substrates via its collagen binding domain (CBD). However, in later stages of biofilm maturation, the same CBD of Cnm self-assembles into amyloid fibrils, losing the ability to bind to collagen and likely becoming a component of the biofilm matrix. Our findings shed light into the role of functional amyloids in S. mutans pathobiology and ecology.

microbiology↗

bioRxiv2020

Homeostatic scaling is driven by a translation-dependent degradation axis that recruits miRISC remodelling

Homeostatic scaling in neurons has been attributed to the individual contribution of either translation or degradation; however there remains limited insight towards understanding how the interplay between the two processes effectuates synaptic homeostasis. Here, we report that a co-dependence between protein synthesis and degradation mechanisms drives synaptic homeostasis whereas abrogation of either prevents it. Coordination between the two processes is achieved through the formation of a tripartite complex between translation regulators, the 26S proteasome and the miRNA-induced-silencing-complex (miRISC) components such as Argonaute, MOV10 and Trim32 on actively translating transcripts or polysomes. The components of this ternary complex directly interact with each other in an RNA-dependent manner. Disruption of polysomes abolishes this ternary interaction, suggesting that translating RNAs facilitate the combinatorial action of the proteasome and the translational apparatus. We identify that synaptic downscaling involves miRISC remodeling which entails the mTORC1-dependent translation of Trim32, an E3 ligase and the subsequent degradation of its target, MOV10 via the phosphorylation of p70 S6 kinase. We find that the E3 ligase Trim32 specifically polyubiquitinates MOV10 for its degradation during synaptic downscaling. MOV10 degradation alone is sufficient to invoke downscaling by enhancing Arc translation through its 3 UTR and causing the subsequent removal of post-synaptic AMPA receptors. Synaptic scaling was occluded when we depleted Trim32 and overexpressed MOV10 in neurons, suggesting that the Trim32-MOV10 axis is necessary for synaptic downscaling. We propose a mechanism that exploits a translation-driven protein degradation paradigm to invoke miRISC remodeling and induce homeostatic scaling during chronic network activity.

neuroscience↗

bioRxiv2018

Vitexin alters Staphylococcus aureus surface hydrophobicity to interfere with biofilm formation.

Bacterial surface hydrophobicity is one of the determinant biophysical parameters of bacterial aggregation for being networked to form biofilm. Phytoconstituents like vitexin have long been in use for their antibacterial effect. The present work is aimed to characterise the effect of vitexin on S. aureus surface hydrophobicity and corresponding aggregation to form biofilm. We have found that vitexin shows minimum inhibitory concentration at 252 g/ml against S. aureus. Vitexin reduces cell surface hydrophobicity and membrane permeability at sub-MIC dose of 126 g/ml. The in silico binding analysis showed higher binding affinity of vitexin with surface proteins of S. aureus. Down regulation of dltA, icaAB and reduction in membrane potential under sub-MIC dose of vitexin, explains reduced S. aureus surface hydrophobicity. Vitexin has substantially reduced the intracellular adhesion of planktonic cells to form biofilm through interference of EPS formation, motility and subsequent execution of virulence. This was supported by the observation that vitexin down regulates the expression of icaAB and agrAC genes of S. aureus. In addition, vitexin also found to potentiate antibiofilm activity of sub-MIC dose of gentamicin and azithromycin. Furthermore, CFU count, histological examination of mouse tissue and immunomodulatory study justifies the in vivo protective effect of vitexin from S. aureus biofilm associated infection. Finally it can be inferred that, vitexin has the ability to modulate S. aureus cell surface hydrophobicity which can further interfere biofilm formation of the bacteria.\n\nImportanceThere has been substantial information known about role of bacterial surface hydrophobicity during attachment of single planktonic bacterial cells to any surface and the subsequent development of mature biofilm. This study presents the effect of flavone phytoconstituent vitexin on modulation of cell surface hydrophobicity in reducing formation of biofilm. Our findings also highlight the ability of vitexin in reducing in vivo S. aureus biofilm which will eventually outcompete the corresponding in vitro antibiofilm effect. Synergistic effect of vitexin on azithromycin and gentamicin point to a regime where development of drug tolerance may be addressed. Our findings explore one probable way of overcoming drug tolerance through application of vitexin in addressing the issue of S. aureus biofilm through modulation of cell surface hydrophobicity.

microbiology↗