Biology subjects

Paul, A.

Publications and source records attributed to Paul, A..

At least 73 records · Page 4Linked to original sources

bioRxiv2023

Biotic Assessment of Crowdsourced Data Defines Four Ecoregions in Thar: A Novel Approach for Citizen Engagement in Conservation

Distinct ecosystems have representative biota that can allow delineation of ecoregions. Despite being one of the most populated desert ecosystems in the world with extreme climatic conditions, Thar has been classified as a single ecoregion by WWF. The present study aimed to test this on the basis of biotic assessment using a citizen science-based crowdsourced data from ebird (492 species of birds through 50,000 checklists of 4000 birders). Unsupervised clustering (k=4) and mathematical validation using cosine similarity revealed the presence of four distinct ecoregionsEastern Thar (ET), Western Thar (WT), Transitional Zone (TZ) and Cultivated Zone (CZ) in Thar. Most strikingly, these ecoregions when overlaid on geographical regions of Thar show that the CZ ecoregion was split between three distant and distinct geographic regions. Further spatial diversity estimates show CZ had the least diversity (273) and highest {beta} diversity (1.8) indicating the least similarity between the districts that comprised this ecoregion. The results suggest CZ as an evolving ecoregion or a consequence of habitat fragmentation due to anthropogenic effects. The presence of least number of exclusive species in CZ (0.2%) and TZ (0.8%) including the near-threatened species like Laticilla burnesii (Rufous-vented grass babbler) and Pelecanus philippensis (Spot-billed pelican) and an endangered species Athene blewitti (Forest Owlet) highlights the need for restoration of these threatened biota and ecoregions. This study for the first time proposes crowd-sourced bird data as an important biota-based tool to understand (a) established ecoregions in an ecosystem, (b) anthropogenic effects of agri-farmlands and (c) relation between geographic regions and biota.

ecology↗

bioRxiv2023

Temporal modification of H3K9/14ac and H3K4me3 histone marks mediates mechano-responsive gene expression during the accommodation process in poplar.

Plants can attenuate their molecular response to repetitive mechanical stimulation as a function of their mechanical history. For instance, a single bending of stem is sufficient to attenuate the gene expression in poplar plants to the subsequent mechanical stimulation, and the state of desensitization can last for several days. The role of histone modifications in memory gene expression and modulating plant response to abiotic or biotic signals is well known. However, such information is still lacking to explain the attenuated expression pattern of mechano-responsive genes in plants under repetitive stimulation. Using poplar as a model plant in this study, we first measured the global level of H3K9/14ac and H3K4me3 marks in the bent stem. The result shows that a single mild bending of the stem for 6 seconds is sufficient to alter the global level of the H3K9/14ac mark in poplar, highlighting the fact that plants are extremely sensitive to mechanical signals. Next, we analyzed the temporal dynamics of these two active histone marks at attenuated (PtaZFP2, PtaXET6, and PtaACA13) and non-attenuated (PtaHRD) mechano-responsive loci during the desensitization and resensitization phases. Enrichment of H3K9/14ac and H3K4me3 in the regulatory region of attenuated genes correlates well with their transient expression pattern after the first bending. Moreover, the levels of H3K4me3 correlate well with their expression pattern after the second bending at desensitization (3 days after the first bending) as well as resensitization (5 days after the first bending) phases. On the other hand, H3K9/14ac status correlates only with their attenuated expression pattern at the desensitization phase. The expression efficiency of the attenuated genes was restored after the second bending in the histone deacetylase inhibitor-treated plants. While both histone modifications contribute to the expression of attenuated genes, mechanostimulated expression of the non-attenuated PtaHRD gene seems to be H3K4me3 dependent.

plant biology↗

bioRxiv2022

Interaction of the Tau fibrils with the neuronal membrane

Tau proteins are gaining a lot of interest recently due to their active role in causing a range of tauopathies. Molecular mechanisms underlying the tau interaction with the neuronal membrane are hitherto unknown and difficult to characterize using conventional experimental methods. Starting from the cryo-EM structure of the tau fibrils, we have used atomistic molecular dynamics simulations to model the interaction between the fibril and neuronal membrane, with explicit solvation. The dynamics and structural characteristics of the tau fibril with the neuronal membrane are compared to the tau fibril in the aqueous phase to corroborate the effect of the neuronal membrane on the tau structure. The tau fibrils are in general more compact in the presence of neuronal membrane compared to their structure in the water medium. We find that the number of {beta} -sheet residues of the tau fibrils are different in the case of two polymorphs, paired helical filament and straight filaments (PHF and SF) in the two media. PHF is found to approach closer to the neuronal membrane than the SF. The negatively charged lipids in the neuronal membrane are found to mediate the tau-neuronal membrane binding. Our study initiates the understanding of tau conformational ensemble in the presence of neuronal membrane and sheds light on the significant tau - membrane interactions. The simulation times of our report might limit the conformational sampling required to observe membrane permeation, nevertheless it provides significant insights into fibril - neuronal membrane interactions.

biophysics↗

bioRxiv2022

Translesion DNA synthesis polymerase kappa functions in the nucleolar stress response

DNA polymerase kappa (Pol{kappa}) has multiple cellular roles such as translesion DNA synthesis, replication of repetitive sequences and nucleotide excision repair. However, the mechanisms regulating Pol{kappa}s cellular activities are unknown. Since all polymerases insert the canonical deoxynucleotide triphosphates, it is difficult to determine which polymerase is active at a particular genomic site. To counter this difficulty, we utilized the selective Pol{kappa} substrate, N2-(4-ethynylbenyl)-2-deoxyguanosine (EBndG), as bait to capture proteins associated with Pol{kappa} synthesized DNA. Here we show that, Pol{kappa} is active in the nucleolus and Pol{kappa} synthesized DNA are enriched with nucleolar proteins. Exposure of cells to benzo[a]pyrene diol epoxide (BPDE) induced hallmarks of nucleolar stress, increased Pol{kappa} stability and nucleolar activity. Other agents that induce nucleolar stress such as mitomycin C, cisplatin and actinomycin D also increased Pol{kappa}s nucleolar activity. The Pol{kappa} activity was cell-cycle independent and dependent on PCNA ubiquitination. In addition, we identified that the expression and activity of Pol{kappa} is regulated by the polycomb complex protein Ring Finger Protein 2 (RNF2) and by poly(ADP)-ribose polymerase 1 (PARP1) catalyzed PARylation. This study provides insight into the novel role of Pol{kappa} in ribosomal RNA synthesis, in maintaining ribosomal DNA integrity after DNA damage thus protecting the cells from nucleolar stress.

molecular biology↗

bioRxiv2022

Comparing lipid remodeling in mouse adipose and liver tissue with quantitative Raman microscopy

Brown adipose tissue (BAT) consists of highly metabolically active adipocytes that catabolize nutrients to produce heat. Playing an active role in triacylglycerol (TAG) clearance, research has shown that dietary fatty acids can modulate the TAG chemistry deposition in BAT after weeks-long dietary intervention, similar to what has been shown in white adipose tissue (WAT). Our objective was to compare the influence of sustained, non-chronic dietary intervention (a one-week interval) on WAT and BAT lipid metabolism and deposition in situ. We use quantitative, label-free chemical microscopy to show that one week of HFD intervention results in dramatically larger lipid droplet (LD) growth in BAT (and liver) compared to LD growth in inguinal WAT (IWAT). Moreover, BAT showed lipid remodeling as increased unsaturated TAGs in LDs, resembling the dietary lipid composition, while WAT (and liver) did not show lipid remodeling on this time scale. Concurrently, expression of genes involved in lipid metabolism, particularly desaturases, was reduced in BAT and liver from HFD-fed mice after one week. Our data show that BAT lipid chemistry remodels exceptionally fast to dietary lipid intervention compared WAT, which further points towards a role in TAG clearance.

cell biology↗

bioRxiv2022

The Effect of Lipid Composition on the Dynamics of Tau Fibrils

Knowledge of the interaction of the tau fibrils with the cell membrane is critical for the understanding of the underlying tauopathy pathogenesis. Lipid composition is found to effect the conformational ensemble of the tau fibrils. Using coarse grained and all-atom molecular dynamics simulations we have shown the effect of the lipid composition in modulating the tau structure and dynamics. Molecular dynamics simulations show that tau proteins interact differentially with the zwitterionic compared to the charged lipid membranes. The negatively charged POPG lipid membranes increase the binding affinity of the tau fibrils. The addition of cholesterol is also found to modify the tau binding to the membrane.

biophysics↗

bioRxiv2022

Babesia divergens egress from host cells is orchestrated by essential and druggable kinases and proteases

A unique aspect of apicomplexan biology is the requirement for egress from and invasion into host red blood cells (RBCs). The cellular mechanisms and molecular mediators of RBC egress and invasion remain poorly characterized in Babesia spp., a group of parasites of veterinary importance and emerging cause of zoonotic disease. Through the use of video microscopy, transcriptomics, and chemical genetics we have implicated signaling, proteases and gliding motility in egress and/or invasion by Babesia divergens. We developed CRISPR/Cas9 and two inducible knockdown systems to perform a genetic screen of putative mediators of egress. We found that proteases ASP2 and ASP3 are required for invasion, and the latter is also required for egress. Strikingly, parasites continue to replicate intracellularly in the absence of the protein kinases, PKG or CDPK4, indicating that they are required for exit from the replication cycle and egress. These essential molecules present druggable targets for Babesia spp. All together we have established a molecular framework for the spread of infection through host RBCs, with egress of B. divergens more closely resembling T. gondii than the more evolutionarily related Plasmodium spp. HighlightsO_LIEgress in Babesia divergens requires host cell lysis and parasite motility C_LIO_LITranscriptomics can be used to identify egress and invasion proteins C_LIO_LIKnockdown of the proteases, ASP2 and ASP3, inhibit egress and invasion C_LIO_LIInhibition of PKG or CDPK4 signaling results in continued intracellular replication C_LI

microbiology↗

bioRxiv2022

Biomechanical dependence of SARS-CoV-2 infections

Older people have been disproportionately vulnerable to the current SARS-CoV-2 pandemic, with an increased risk of severe complications and death compared to other age groups. A mix of underlying factors has been speculated to give rise to this differential infection outcome, including changes in lung physiology, weakened immunity, and severe immune response. Our study focuses on the impact of biomechanical changes in lungs that occur as individuals age, i.e., the stiffening of the lung parenchyma and increased matrix fiber density. We used hydrogels with an elastic modulus of 0.2 and 50 kPa and conventional tissue culture surfaces to investigate how infection rate changes with parenchymal tissue stiffness in lung epithelial cells challenged with SARS-CoV-2 Spike (S) protein pseudotyped lentiviruses. Further, we employed electrospun fiber matrices to isolate the effect of matrix density. Given the recent data highlighting the importance of alternative virulent strains, we included both the native strain identified in early 2020 and an early S protein variant (D614G) that was shown to increase the viral infectivity markedly. Our results show that cells on softer and sparser scaffolds, closer resembling younger lungs, exhibit higher infection rates by the WT and D614G variant. This suggests that natural changes in lung biomechanics do not increase the propensity for SARS-CoV-2 infection and that other factors, such as a weaker immune system, may contribute to increased disease burden in the elderly.

bioengineering↗

bioRxiv2021

ESR2 regulates indian hedgehog signaling in neonatal rat ovary

The transcriptional regulatory function of estrogen receptor {beta} (ESR2) is essential for the regulation of primordial follicle activation (PFA). Increased PFA due to the loss of ESR2 becomes evident as early as postnatal day 8 (PND8). To identify the ESR2-regulated genes that control PFA, we performed RNA-seq analyses of wildtype, and Esr2 knockout (Esr2KO) neonatal rat ovaries collected on PND4, PND6, and PND8. Among the differentially expressed genes in Esr2KO ovaries, indian hedgehog (Ihh) displayed the highest downregulation among the ovary enriched genes. IHH regulated genes including Hhip as well as the steroidogenic enzymes were also downregulated in Esr2KO rat ovaries. Remarkably, the expression of Ihh in Esr2KO ovaries was not upregulated despite the high levels of Gdf9 and Bmp15, which are known regulators of Ihh expression in granulosa cells. Our findings suggest that indian hedgehog signaling in the neonatal rat ovary is dependent on ESR2.

developmental biology↗

bioRxiv2021

Long-Range Electrostatic Interactions Significantly Modulate the Affinity of Dynein for Microtubules

The dynein family of microtubule minus-end directed motor proteins drives diverse functions in eukaryotic cells, including cell division, intracellular transport, and flagellar beating. Motor protein processivity, which characterizes how far a motor walks before detaching from its filament, depends on the interaction between its microtubule-binding domain (MTBD) and the microtubule. Dyneins MTBD switches between high- and low-binding affinity states as it steps. Significant structural and functional data show that specific salt bridges within the MTBD and between the MTBD and the microtubule govern these affinity state shifts. However, recent computational work suggests that non-specific, long-range electrostatic interactions between the MTBD and the microtubule may also play a significant role in the processivity of dynein. To investigate this hypothesis, we mutated negatively charged amino acids remote from the dynein MTBD-microtubule-binding interface to neutral residues and measured the binding affinity using microscale thermophoresis and optical tweezers. We found a significant increase in the binding affinity of the mutated MTBDs for microtubules. Furthermore, we found that charge screening by free ions in solution differentially affected the binding and unbinding rates of MTBDs to microtubules. Together, these results demonstrate a significant role for long-range electrostatic interactions in regulating dynein-microtubule affinity. Moreover, these results provide insight into the principles that potentially underlie the biophysical differences between molecular motors with various processivities and protein-protein interactions more generally. Statement of SignificanceThe dynein family of motor proteins drives the motility of multiple cellular functions by walking toward the minus end of microtubules. The biophysical mechanisms of dynein rely on its ability to change affinity for the microtubule as it steps. Specific short-range electrostatic interactions acting at the microtubule-binding domain (MTBD)-microtubule interface are known to govern binding affinity. This study shows that non-specific longer-range electrostatic interactions due to charged amino acids remote from the binding interface also contribute significantly to the binding affinity mechanisms. Our results suggest that subtle differences in the electrostatic charge distribution within the MTBD significantly affect the molecular biophysical motility mechanisms in the dynein family of motors.

biophysics↗

bioRxiv2021

Calculating the force-dependent unbinding rate of biological macromolecular bonds from the force-ramp optical trapping assays

The non-covalent biological bonds that constitute protein-protein or protein-ligand interactions play crucial roles in many cellular functions, including mitosis, motility, and cell-cell adhesion. The effect of external force (F) on the unbinding rate (koff(F)) of macromolecular interactions is a crucial parameter to understanding the mechanisms behind these functions. Optical tweezer-based single-molecule force spectroscopy is frequently used to obtain quantitative force-dependent dissociation data on slip, catch, and ideal bonds. However, analyses of this data using dissociation time or dissociation force histograms often quantitatively compare bonds without fully characterizing their underlying biophysical properties. Additionally, the results of histogram-based analyses can depend on the rate at which force was applied during the experiment and the experiments sensitivity. Here, we present an analytically derived cumulative distribution function-like approach to analyzing force-dependent dissociation force spectroscopy data. We demonstrate the benefits and limitations of the technique using stochastic simulations of various bond types. We show that it can be used to obtain the detachment rate and force sensitivity of biological macromolecular bonds from force spectroscopy experiments by explicitly accounting for loading rate and noisy data. We also discuss the implications of our results on using optical tweezers to collect force-dependent dissociation data.

biophysics↗

bioRxiv2021

Co-aggregation and secondary nucleation in the life cycle of human prolactin/galanin functional amyloids

Synergistic-aggregation and cross-seeding by two different amyloid proteins/peptides are well evident in various neurological disorders. However, this phenomenon is not well studied in functional amyloid aggregation. Here, we show Prolactin (PRL) is associated with lactation in mammals and neuropeptide galanin (GAL), which are co-stored in the lactotrophs facilitates the synergic aggregation in the absence of secretory granules helper molecules glycosaminoglycans (GAGS). Interestingly, although each partner possesses homotypic seeding ability, a unidirectional cross-seeding of GAL aggregation can be mediated by PRL seeds. The specificity of co-aggregation by PRL and GAL along with unidirectional cross-seeding suggests tight regulation of functional amyloid formation during co-storage of these hormones in secretory granule biogenesis of female rat lactotrophs. Further mixed fibrils release the constituent functional hormone much faster than the corresponding individual amyloid formed in presence of GAGs, suggesting that co-aggregation of functionally distant hormones might have evolved for efficient storage, synergistic and rapid release of both hormones upon stimulation. The co-aggregation and cross seeding by two different hormones of completely different structures and sequences (PRL and GAL) suggest a novel mechanism of heterologous amyloid formation both in disease and functional amyloids.

biophysics↗

bioRxiv2021

Selective MAP1LC3C (LC3C) autophagy requires noncanonical initiation regulators and the paralog-specific C-terminal peptide

LC3s are canonical proteins necessary for the formation of autophagosomes. We have previously established that two paralogs, LC3B and LC3C, have opposite activities in renal cancer, with LC3B playing oncogenic role and LC3C tumor suppressing role. LC3C is an evolutionary late gene, present only in higher primates and humans. Its most distinct feature is a C-terminal 20 amino acid peptide cleaved in the process of glycine 126 lipidation. Here we investigated mechanisms of LC3C selective autophagy. LC3C autophagy requires noncanonical upstream regulatory complexes that include ULK3, UVRAG, RUBCN, PIK3C2A, and a member of ESCRT, TSG101. We established that Postdivision Midbody Rings (PDMBs) implicated in cancer stem cell regulation are direct targets of LC3C autophagy. LC3C C-terminal peptide is necessary and sufficient to mediate LC3C-dependent selective degradation of PDMBs. This work establishes a new noncanonical human-specific selective autophagic program relevant to cancer stem cells.

cancer biology↗

bioRxiv2020

Septal HDAC1 facilitates long-lasting extinction of social fear in male mice

Social anxiety disorder (SAD) is primarily caused by traumatic social events and is characterized by intense fear and avoidance of socially enriched contexts. Formation of such intense social aversion requires learning of the association between trauma and originally neutral social stimuli. Acetylation of histones in response to learning is critical for long-term memory formation. Class I histone deacetylases (HDACs) have emerged as powerful negative regulators of long-term memory formation. However, the lack of clarity in isoform and spatial specificity in HDAC function exists. Utilizing the social fear conditioning (SFC) as well as cued fear conditioning (CFC) paradigms, we aimed to functionally characterize the role of class I HDACs, especially HDAC1, in the regulation of aversive memories in social versus non-social contexts. Using cFos expression as a marker of cellular activity, we revealed that the lateral septum (LS) was specifically activated post-acquisition in socially fear conditioned (SFC+) mice. We further measured an increase in activity-inducing HDAC1 phosphorylation at serine residues within the septum of SFC+ mice during extinction of social fear. Pharmacological inhibition of HDAC1 within the LS facilitated, while viral overexpression of septal HDAC1 impaired extinction of social fear. Finally, we found that the abovementioned facilitation of extinction memory by HDAC1 inhibition was long-lasting and persists even after 30 days of extinction. Our results show that LS-HDAC1 is a key regulator of long-lasting social fear extinction, which points towards HDAC1 as a potential therapeutic target for SAD.

neuroscience↗

bioRxiv2020

Detection and genetic analysis of infectious spleen and kidney necrosis virus (ISKNV) in ornamental fish from non-clinical cases: First report from India

Infectious spleen and kidney necrosis virus (ISKNV), a type species of the genus Megalocytivirus, poses a threat to ornamental fish trade as most cases show nonspecific symptoms, thus making timely diagnosis challenging. Apparently health molly (Poecilia sphenops) and angelfish (Pterophyllum scalare) collected from two distinct geographic localities of India were screened for four genera under Iridoviridae, Megalocytivirus i.e, ISKNV, turbot reddish body iridovirus (TRBIV) and red seabream iridovirus (RSIV); ranaviruses and Singapore grouper iridovirus; and Lymphocystivirus through molecular approach. In total seven numbers out of 35 samples (20%), ISKNV genome fragments were detected. A PCR assay using major capsid protein (MCP) gene was standardised to detect and differentiate infections within the Megalocytivirus genus, even without aid of sequencing. This forms the first report of ISKNV infection in ornamental fish from India. Moreover, the ISKNV infection was confirmed by PCR and sequence analysis of MCP and ATPase genes. The sequence of these genes showed that Indian isolate being 99-100% similar to the complete genome or reference strain of ISKNV. Phylogenetic reconstruction demonstrated the present strain belonging to ISKNV genotype I. Furthermore, structural stability of the MCP revealed this strain was more stable than ISKNV genotype II, RSIV and TRBIV at 25{degrees}C and pH 7.0. Thus, strong pan-India surveillance is recommended to reduce trade risk.

microbiology↗

bioRxiv2020

Thermodynamics and kinetics of the amyloid-β peptide revealed by Markov state models based on MD data in agreement with experiment

The amlyoid-{beta} peptide (A{beta}) is closely linked to the development of Alzheimers disease. Molecular dynamics (MD) simulations have become an indispensable tool for studying the behavior of this peptide at the (sub)molecular level, thereby providing insight into the molecular basis of Alzheimers disease. General key aspects of MD simulations are the force field used for modeling the peptide or protein and its environment, which is important for accurate modeling of the system of interest, and the length of the simulations, which determines whether or not equilibrium is reached. In this study we address these points by analyzing 30-{micro}s MD simulations acquired for A{beta}40 using seven different force fields. We assess the convergence of these simulations based on the convergence of various structural properties and of NMR and fluorescence spectroscopic observables. Moreover, we calculate Markov state models for each of the seven MD simulations, which provide an unprecedented view of the thermodynamics and kinetics of the amyloid-{beta} peptide. This further allows us to provide answers for pertinent questions, like: Which force fields are suitable for modeling A{beta}? (a99SB-UCB and a99SB-ILDN/TIP4P-D); What does A{beta} peptide really look like? (mostly extended and disordered) and; How long does it take MD simulations of A{beta} to attain equilibrium? (20-30 {micro}s). We believe the analyses presented in this study will provide a useful reference guide for important questions relating to the structure and dynamics of A{beta}in particular, and by extension other similar disordered peptides.

biophysics↗

bioRxiv2020

Molecular dynamics simulations of protein aggregation: protocols for simulation setup and analysis with Markov state models and transition networks

Protein disorder and aggregation play significant roles in the pathogenesis of numerous neuro-degenerative diseases, such as Alzheimers and Parkinsons disease. The end products of the aggregation process in these diseases are {beta}-sheet rich amyloid fibrils. Though in most cases small, soluble oligomers formed during amyloid aggregation are the toxic species. A full understanding of the physicochemical forces behind the protein aggregation process is required if one aims to reveal the molecular basis of the various amyloid diseases. Among a multitude of biophysical and biochemical techniques that are employed for studying protein aggregation, molecular dynamics (MD) simulations at the atomic level provide the highest temporal and spatial resolution of this process, capturing key steps during the formation of amyloid oligomers. Here we provide a step-by-step guide for setting up, running, and analyzing MD simulations of aggregating peptides using GROMACS. For the analysis we provide the scripts that were developed in our lab, which allow to determine the oligomer size and inter-peptide contacts that drive the aggregation process. Moreover, we explain and provide the tools to derive Markov state models and transition networks from MD data of peptide aggregation.

biophysics↗

bioRxiv2019

Unveiling the physiological mechanisms that drive the emergence of antibiotic resisters from antibiotic persister population of mycobacteria

The physiological mechanisms behind the emergence of antibiotic-resistant bacteria from their antibiotic-persister population are beginning to be explored. Here we delineate the sequential physiological events that drive the emergence of rifampin-resistant rpoB mutants from rifampin-persister population of mycobacteria during prolonged exposure. The rifampin-persister population generated elevated levels of hydroxyl radical, which inflicted mutations, enabling regrowth of the persister cells to form multi-septated, multi-nucleated elongated cells. These cells, through multiple divisions, produced multiple sister-daughter cells, causing an abrupt, unexpectedly high increase of rifampin-resistant colonies. Similar response was observed against moxifloxacin also. Earlier studies on the rifampin/moxifloxacin-exposed laboratory/clinical M. tuberculosis strains from in-vitro cultures and infected mouse-lung also showed cfu spurt, but went unnoticed/unreported. It is likely that these sequential physiological events may be driving the emergence of antibiotic-resistant tubercle bacilli in TB patients also. Escherichia coli also has been found to respond similarly against subminimal inhibitory concentrations of ciprofloxacin. Thus, the present findings attain broad significance as a general physiological mechanism used by diverse bacterial genera to emerge as drug-resistant strains against antibiotics.

microbiology↗