Biology subjects

Mukherjee, C.

Publications and source records attributed to Mukherjee, C..

At least 19 recordsLinked to original sources

bioRxiv2026

Cytoplasmic recapping commences the translation of a micropeptide, MARS from MALAT1 after the removal of an inhibitory RNA G-quadruplex

Long non-coding RNAs (lncRNAs), conventionally defined as RNA transcripts longer than 200 nucleotides that lack protein-coding potential, have emerged as key regulators of diverse biological processes, including metabolism, development, cellular differentiation, and stress responses. They modulate cellular functions through multiple mechanisms, including chromatin remodeling, transcriptional regulation, and the control of RNA stability and translation. Most lncRNAs are transcribed by RNA polymerase II and undergo canonical RNA processing, including splicing, polyadenylation, and 5' N7-methylguanosine (mG) capping. However, whether cytoplasmic recapping of lncRNAs can promote the production of functional micropeptides remains poorly understood. In this study, we investigated the functional consequences of cytoplasmic recapping of MALAT1, a highly abundant and broadly expressed lncRNA. We demonstrate that cytoplasmic processing and recapping of a MALAT1 decay intermediate support the production of a previously uncharacterized micropeptide, designated MARS (MALAT1 Responsive to Stress). We further identify RNA G-quadruplex (rG4) structures in the 5' region of MALAT1 that inhibit MARS translation, revealing an additional layer of structural regulation. MARS expression increases in response to arsenite-induced oxidative stress and is associated with nuclear factor erythroid 2-related factor 2 (Nrf2)-containing complexes. Furthermore, MARS is implicated in the regulation of antioxidant response element-associated genes, including SOD and CAT, suggesting a potential role in cellular antioxidant defense. Collectively, our findings identify a previously unrecognized functional output of cytoplasmic RNA recapping and expand the potential coding repertoire of lncRNAs. This study highlights a mechanism through which cytoplasmic RNA processing may contribute to micropeptide production and suggests a role for MALAT1-derived MARS in oxidative stress-responsive gene regulation.

molecular biology↗

bioRxiv2026

Cytoplasmic capping enzyme targeted, hypoxia-responsive RNAs, RORA and KCTD16 modulate the aggressiveness of CoCl2-induced hypoxic osteosarcoma cells

Hypoxia is a defining feature of the solid tumour microenvironment and a major determinant of therapeutic response. Hypoxia-inducible factors (HIFs) are central regulators of transcriptional reprogramming under hypoxic stress. Hypoxia can paradoxically elicit both tumour-promoting and tumour-suppressive outcomes, suggesting regulatory mechanisms beyond canonical HIF-dependent pathways. Emerging evidence indicates that hypoxia-responsive RNAs (HRRs) may also be regulated independently of HIFs, with posttranscriptional stabilization playing a critical determinant of hypoxic adaptation. Cytoplasmic mRNA recapping mediated by the cytoplasmic capping enzyme (cCE) has recently emerged as an important post-transcriptional regulatory process, yet its role in hypoxia-driven RNA regulation remains poorly understood. Here, we aimed to identify novel HRRs that modulate cellular adaptability to hypoxia and to determine whether these transcripts are regulated by cCE. Using CoCl2-induced hypoxia, we observed a significant reduction in osteosarcoma cell aggressiveness, characterized by decreased proliferation, clonogenic survival, and migratory capacity. Transcriptomic profiling of hypoxic osteosarcoma cells identified RORA and KCTD16 as significantly upregulated and function as suppressors of tumour cell aggressiveness. Integrative in-silico CAGE tag analysis followed by cap-specific biochemical assays confirmed that both transcripts are post-transcriptionally stabilized by cCE. Mechanistically, hypoxia-induced stabilization of HIF1 transcriptionally elevated RORA and KCTD16 expression, while cCE further reinforced their stability post-transcriptionally. Stabilization of these cCE-targeted HRRs resulted in suppression of the oncogenic proliferation driver c-Myc, thereby attenuating the aggressive phenotype of hypoxic osteosarcoma cells. Collectively, our findings identify cCE as a previously unrecognized post-transcriptional regulator in hypoxia biology and reveal a RNA-centric mechanism by which hypoxia can restrain tumour aggressiveness.

molecular biology↗

bioRxiv2025

A Transformer based method for the Cap Analysis of Gene Expression and Gene Expression Tag associated 5' cap site prediction in RNA

5 RNA capping is one of the major post-transcriptional modifications for the mobility and stability of RNA molecules. Measuring 5 caps of RNAs can help quantify expression levels of mRNAs and lncRNAs. One of the most successful RNAseq methods that have used capping as a tool to quantify expression of transcription is Cap Analysis of Gene Expression(CAGE). Computational prediction of capping can therefore be used as a precursor to the prediction of transcriptional expression. Unfortunately, there is hardly any computational technique that has focused purely on predicting 5 capping. We have developed a transformer-based method for computational prediction of capping from DNA sequences. Our Llama and ReLoRA-based pre-training model, and Llama and LoRA-based fine-tuning model predict 5 cap sites. We have used Leave-one-chromosome-out-cross-validation for our model. The average accuracy, and F1-score after fine-tuning the human genome hg19(mouse genome mm9) for sequence classification is 79.12%(78.09%), and 78.11%(76.17%), respectively. We noted attention peak-based motifs having an aggregate Wilcoxon rank-sum p-value of 1.075e-10 between the attention peak region and the entire context window for the predicted positive motifs; an aggregate p-value of 7.17e-18 for the predicted negative motifs; and an aggregate p-value of 6.70e-08 between the attention peaks of the predicted positive and the predicted negative motifs. Our Llama-based approach aims to create a sequence-based framework to identify 5 capping sites corresponding to CAGE peaks. Our analysis reveals statistically significant motifs from the regions of peak attention scores, which demonstrates biological relevance for some through their resident sites matching with known TF motifs.

bioinformatics↗

bioRxiv2025

AP-3 complex sorts preferential cargo to govern dense core vesicle function in neuroendocrine cells

This study reveals new insights into the role of the Adaptor protein (AP-3) complex in dense core vesicle function. Despite numerous studies, an existing knowledge lacuna in the role of AP-3 in DCV function prompted us to delve deeper. Advanced microscopy and biochemical analysis revealed compromised DCV exocytosis in AP-3-depleted PC12 cells and C. elegans. AP-3 depletion altered the size and positioning of DCVs. Golgi defects and RUSH (Retention under Selective Hook) substantiated the role of AP-3 in trans-Golgi DCV budding. Proteomics revealed the loss of specific known and putative novel DCV proteins, which were mislocalized and rerouted to lysosomes in AP-3-depleted cells. Bioinformatics, Proximity ligation assays and Co-immunoprecipitation identified interactions of mislocalized proteins with AP-3 subunit. These findings corroborated with functional defects in granule maturation, release modes, Zinc and neurotransmitter mobilisation. Our study highlights the complexity of the AP-3 complex in regulating DCV function and its importance in vesicle transport in neurons and neuroendocrine cells. SummaryThis work reveals the critical role of AP-3 complex in DCV function, highlighting its impact on DCV exocytosis, positioning, and trans-Golgi budding. This study identifies Dlk1 as a novel DCV cargo.

cell biology↗

bioRxiv2025

Integrative Chemical Genetics Platform Identifies Condensate Modulators Linked to Neurological Disorders

Aberrant biomolecular condensates are implicated in neurological disorders including ALS, frontotemporal dementia, and DYT1 dystonia, yet approaches to systematically identify their modulators remain limited. Here we establish MLF2 as a versatile condensate biomarker and develop CondenScreen, an integrated high-content screening and bioinformatic pipeline enabling identification of condensate modulators across chemical and genetic space. Screening 1,760 FDA-approved compounds in a cellular DYT1 dystonia model, we identify drugs that alter aberrant condensate properties, validating the platform for condensate-targeted drug discovery. In parallel, a genome-wide CRISPR/Cas9 screen links condensate accumulation to microcephaly genes and more than 10 additional neurodevelopmental disorders. Machine learning and confocal imaging resolves distinct condensate phenotypes: loss of microcephaly-associated ZNF335 results in nucleoplasmic condensates, whereas RNF26 deletion produces nuclear envelope condensates that phenocopy hallmarks of torsin deficiency. Our study provides a scalable resource for identifying corrective modulators of condensates and establishes a link between nuclear condensate accumulation and neurodevelopmental disorders.

cell biology↗

bioRxiv2024

Identification of transcriptome-wide cobalt chloride-induced hypoxia-responsive long noncoding RNAs regulated by cytoplasmic mRNA capping enzyme

Long non-coding RNAs (lncRNAs) are key regulators of gene expression in human cancers, influencing tumor microenvironment (TME). Hypoxia, a hallmark of solid tumors, elevates hypoxia-inducible factor 1 (HIF-1), which regulates hypoxia-responsive lncRNAs (HRLs). These HRLs are essential in regulating gene expression under hypoxic conditions at both transcriptional and post-transcriptional levels. However, the mechanisms governing the post-transcriptional regulation of lncRNAs are not fully understood. It has been shown that the cytoplasmic pool of mRNA capping enzyme (cCE) can post-transcriptionally regulate its substrate uncapped mRNAs and lncRNAs in the cytoplasm, thereby preventing their degradation. Our previous study showed elevated expression of cCE under hypoxic conditions. This study aimed to determine whether cCE influences the transcriptome-wide HRLs in CoCl2-induced hypoxia in osteosarcoma U2OS cells. We identified 306 known lncRNAs with significant differential expression under hypoxic conditions, including 137 upregulated and 169 downregulated by RNA sequencing. Gene Ontology enrichment analysis revealed their distinct association with various cancers. Our investigation aimed to ascertain whether the cCE post-transcriptionally regulates these HRLs. Overexpression of a dominant negative form of cCE suggested cCE might post-transcriptionally regulate these HRLs. Future research should focus on understanding how cCE influences substrate HRLs, which play a crucial role in the bidirectional signaling circuit between TME and cancer cells under hypoxic stress as well as establishing cCE as a key factor that may alter cellular responses to hypoxia by stabilizing cCE-targeted lncRNAs.

molecular biology↗

bioRxiv2024

Automated Navigation of the lncRNA Transcriptome: A comprehensive SnakeMake based computational Pipeline for robust Identification of lncRNAs and their putative targets

BackgroundLong non-coding RNAs (lncRNAs) have emerged as potent regulatory elements in cellular processes. The substantial increase in transcriptomic data resulting from high-throughput RNA sequencing necessitates effective approaches for the identification and functional annotation of lncRNAs. MethodTo address this need, we have developed a SnakeMake-based pipeline. Our pipeline automates and integrates several key steps: 1) RNA-seq analysis using Hisat2 and stringTie, (2) lncRNA identification using inhouse python scripts and tools CPC2 and BLASTX, (3) prediction of cis- and trans- gene targets of lncRNAs, and (4) KEGG pathway enrichment to obtain biological insights. Importantly, the pipeline allows users to customize parameters for each step through a user-friendly configuration file (config.yaml), enhancing flexibility and ease of use. One of the distinctive features of our approach is its single command execution, facilitating multiple runs without the need for extensive user intervention. This not only enhances user convenience but also ensures reproducibility of analyses across different studies. ResultWe applied our pipeline on rice, sorghum, and human RNA-seq data, to identify (1) List of all differentially expressed transcripts., (2) List of differentially expressed lncRNAs, (3) lncRNA target genes, (4) Enriched pathways to which target genes belong and (5) Obtain a visualization output in the form of a bubble plot that depicts the enriched pathways. Our approach can help researchers obtain valuable biological insights into how lncRNAs contribute to various biological functions. ConclusionThe distinctive features of our SnakeMake-based automation pipeline position it as a versatile asset for researchers seeking a user-friendly, adaptable, robust, and reproducible solution for pan species lncRNA analysis. By efficiently uncovering the regulatory roles of lncRNAs in cellular processes, this pipeline has the potential to shed light on various biological phenomena, such as developmental biology, disease progression, and cellular response to external stimuli. GRAPHICAL ABSTRACTThis study presents a SnakeMake-based pipeline for identifying and annotating long non-coding RNAs (IncRNAs) from RNA sequencing data. It integrates RNA-seq analysis, IncRNA identification, gene target prediction, and pathway enrichment, with customizable parameters through a user-friendly configuration file. The pipelines single command execution enhances convenience and reproducibility. (The bubble chart in the figure is a representative chart and provided as an example.) O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=96 SRC="FIGDIR/small/608522v1_ufig1.gif" ALT="Figure 1"> View larger version (26K): org.highwire.dtl.DTLVardef@9e2930org.highwire.dtl.DTLVardef@1a219e9org.highwire.dtl.DTLVardef@153462dorg.highwire.dtl.DTLVardef@243d3d_HPS_FORMAT_FIGEXP M_FIG C_FIG

bioinformatics↗

bioRxiv2024

Cytoplasmic mRNA capping enzyme is regulated by hypoxia inducible factor HIF1α and controls stability of the target lncRNAs during hypoxia

In response to hypoxia, hypoxia-inducible factors (HIFs) control the transcriptomic output to mitigate the hypoxic stress. Long noncoding RNAs (lncRNA) are found to be very crucial in regulating hypoxia. Like mRNAs, lncRNAs are protected by 5 caps that are added by mRNA capping enzyme (CE) in the nucleus. The previous concept that capping takes place in the nucleus was changed by the recognition of a cytoplasmic pool of capping enzyme (cCE). cCE has been shown to recap its substrate uncapped mRNAs or long noncoding RNAs (lncRNAs) present in the cytoplasm, preventing their degradation, even during arsenite-induced oxidative stress. In this study, we examined the effect of CoCl2 induced hypoxia on cCE and its function in regulating the substrate lncRNAs. Here, we show that CoCl2 induced hypoxia elevates the expressions of nuclear and cytoplasmic CE in HIF1 dependent manner as evidenced by Chromatin immunoprecipitation and HIF1 inhibitor experiments. Furthermore, we found cCE post-transcriptionally controls the stability of its target lncRNAs amidst CoCl2 induced hypoxia. These results suggest that cCE, upregulated by HIF1, may act as a posttranscriptional modulator for a few cCE-targeted lncRNAs.

molecular biology↗

bioRxiv2023

Sida cordifolia, a medicinal plant is efficacious in models of Huntingtons disease, by reducing ER stress

Background and aimHuntingtons Disease is a severe neurodegenerative disorder caused by misfolded mutant huntingtin proteins with expanded stretches of polyglutamines aggregating and destroying cells in the nervous system. Sida cordifolia and Acorus calamus are medicinal plants used in traditional Ayurvedic medicine to treat neurological disorders. Here, we tested the effectiveness of extracts of both medicinal plants in decreasing aggregation of mutant huntingtin protein in models of Huntingtons Disease and explored the mode of action. Experimental procedureWe used two models, the nematode Caenorhabditis elegans and a transgenic mouse neuroblastoma cell line, both expressing mutant huntingtin proteins with elongated polyglutamines. We assessed the effect of Sida cordifolia and Acorus calamus on mutant huntingtin protein aggregation in both models, and additionally used the cell line for mechanistic studies to identify cellular pathways underlying the effects of treatment. Results and conclusionHere, we show that an extract of Sida cordifolia inhibits aggregation of mutant huntingtin proteins. In the C. elegans model, the extract prolonged life span and improved motility of the nematode by reducing aggregation of the mutant huntingtin protein. Acorus calamus did not exhibit these effects. In the transgenic mouse neuroblastoma cell line, the extract decreased aggregation of the mutant huntingtin protein by suppressing key pathways in the ER stress response caused by the mutant protein. Our results highlight the potential therapeutic value of Sida cordifolia and its promise as a source for novel medications. HighlightsO_LISida cordifolia extract reduces aggregates in HD model of transgenic worms C_LIO_LIReduction in aggregates leads to improved motility and longevity C_LIO_LISida cordifolia extract reduces ER stress in cells expressing mHTT protein C_LIO_LIFirst report on the pharmacology of Sida cordifolia in neurodegeneration C_LI

pharmacology and toxicology↗

bioRxiv2023

Mild ER Stress Impedes Regulated Secretion By Governing Key Exocytotic and granulogenic Molecular Switches

Dense core vesicles (DCVs) and synaptic vesicles (SVs) are specialised secretory vesicles (SSVs) in neurons/neuroendocrine cells harbouring cargo whose abnormal release is associated with pathophysiology. Endoplasmic Reticulum (ER) stress and inter-organellar communication are also associated with disease biology. In pursuit of investigating the cell physiological consequences arising from the crosstalk of a stressed ER and DCVs, ER stress was modelled in PC12 neuroendocrine cells using Thapsigargin (Tg). DCV exocytosis was severely compromised in ER-stressed PC12 cells, reversed by Docosahexaenoic acid (DHA). Experiments with Tunicamycin(Tm), an independent ER stressor, yielded similar results. Concurrently, ER stress caused impaired DCV exocytosis also in INS-1 cells. Molecular analysis revealed blunted SNAP25 expression, potentially attributed to augmented levels of ATF4 (a well-known CREB inhibitor) and its transcriptional regulator CREB (also known to regulate key granulogenic players Chromogranin A, Secretogranin II). Our studies revealed severe defects in DCV exocytosis in ER-stressed cells for the first time, mediated by reduced levels of key exocytotic and granulogenic switches regulated via the CREB/ATF4/eIF2 axis.

cell biology↗

bioRxiv2023

Increase in primary cilia number and length upon VDAC1 depletion contributes to attenuated proliferation of cancer cells

Primary cilia (PCs) that are present in most human cells and perform sensory function or signal transduction are lost in many solid tumors. Previously, we identified VDAC1, best known to regulate mitochondrial bioenergetics, to negatively regulate ciliogenesis. Here, we show that downregulation of VDAC1 in pancreatic cancer-derived Panc1 and glioblastoma-derived U-87 cells significantly increased ciliation. Those PCs were remarkably longer than the control cells. Such increased ciliation inhibited cell cycle, which contributed to reduced proliferation of these cells. VDAC1-depletion also led to longer PCs in quiescent RPE1 cells. Therefore, serum-induced PC disassembly was slower in VDAC1-depleted RPE1 cells. Overall, this study reiterates the importance of VDAC1 in modulating tumorigenesis, due to its novel role in regulating PC length and disassembly.

cell biology↗

bioRxiv2023

mRNA capping enzyme exports to cytoplasm, localizes to stress granules and maintains cap homeostasis of the target mRNAs

mRNA decapping is believed to trigger RNA degradation until the identification of cytoplasmic capping that has changed the epitome of RNA stability. Unlike nuclear capping machinery that includes RNA polymerase II bound mRNA Capping Enzyme (CE), N-7 RNA methyl transferase and RNMT activating protein RAM, cytoplasmic capping complex consist of cytoplasmic pool of CE (cCE) and N-7 RNA methyl transferase-RAM along with a few cytoplasmic proteins of various functions. Cytoplasmic capping has been shown to recap selective uncapped mRNAs and maintains cap homeostasis by a cyclic process of decapping and recapping. Thus, it acts as post-transcriptional nexus for the target transcripts. Our data show nuclear export of mammalian CE is regulated by Exportin1 (XPO1) pathway via a conserved Nuclear Export Signal sequence. In order to examine biological function of cCE, we show cCE forms granules during stress and majority of these granules co-localize with SGs. In order to identify how cCE regulates cap homeostasis during stress and recovery, we measured the cap status of specific cCE targeted mRNA transcripts along with non-targeted transcripts during non-stress, stress and recovery phase using Xrm1 susceptibility assay. Our data show cCE targeted mRNA transcripts lost their caps in stress condition when cCE is sequestered in granules. After removal of stress, when cCE is released, the cap status has been restored for these transcripts pointing towards the role of cCE in altering cap homeostasis and thus promoting cellular recovery from stress.

molecular biology↗

bioRxiv2022

UltraSEQ: a universal bioinformatic platform for information-based clinical metagenomics and beyond

Applied metagenomics is a powerful emerging capability enabling untargeted detection of pathogens, and its application in clinical diagnostics promises to alleviate the limitations of current targeted assays. While metagenomics offers a hypothesis-free approach to identify any pathogen, including unculturable and potentially novel pathogens, its application in clinical diagnostics has so far been limited by workflow-specific requirements, computational constraints, and lengthy expert review requirements. To address these challenges, we developed UltraSEQ, a first-of its kind metagenomics-based clinical diagnostics and biosurveillance tool that is accurate and scalable. Here we present results for evaluation of our novel UltraSEQ pipeline using an in silico synthesized metagenome, mock microbial community datasets, and publicly available clinical datasets from samples of different infection types, and both short-read and long-read sequencing data. Our results show that UltraSEQ successfully detected all expected species across the tree of life in the in silico sample and detected all 10 bacterial and fungal species in the mock microbial community dataset. For clinical datasets, even without requiring dataset-specific configuration settings changes, background sample subtraction, or prior sample information, UltraSEQ achieved an overall accuracy of 91%. Further, we demonstrated UltraSEQs ability to provide accurate antibiotic resistance and virulence factor genotypes that are consistent with phenotypic results. Taken together, the above results demonstrates that the UltraSEQ platform offers a transformative approach to microbial and metagenomic sample characterization, employing a biologically informed detection logic, deep metadata, and a flexible system architecture for classification and characterization of taxonomic origin, gene function, and user-defined functions, including disease-causing infection.

bioinformatics↗

bioRxiv2022

Identification of Long noncoding RNAs as substrate of cytoplasmic Capping Enzyme

Cytoplasmic capping returns a cap to specific mRNAs thus protecting uncapped RNAs from decay. Prior to the identification of cytoplasmic capping, uncapped mRNAs were thought to be degraded. Here, we test whether long non-coding RNAs (lncRNAs) are cytoplasmic capping enzyme (cCE) substrates. The subcellular localization of fourteen lncRNAs associated with sarcomas were examined in U2OS osteosarcoma cells. We used 5 rapid amplification of cDNA ends (RACE) to assay uncapped forms of these lncRNAs. Inhibiting cytoplasmic capping elevated uncapped forms of selected lncRNAs indicating a plausible role of cCE in targeting them. Analysis of published cap analysis of gene expression (CAGE) data shows increased prevalence of certain 5-RACE cloned sequences suggesting that these uncapped lncRNAs are cytoplasmic capping targets.

molecular biology↗

bioRxiv2022

Microdynamics of lamin A Ig-fold domain regulates higher order assembly of the protein

Lamins maintain the shape and rigidity of the nucleus in the form of a proteinaceous scaffold underneath the inner nuclear membrane (INM) and provide anchorage to chromatin and other nuclear proteins. Mutations in the human LMNA gene encoding lamin A/C cause about 16 different diseases with distinct phenotypes collectively termed as laminopathies which affect primarily the muscle tissues as well as adipose tissues, neuromuscular junctions and multiple other organs in progeroid syndromes. Lamins contain several domains of which Ig-fold is one of the well characterized and structured domains that harbours many mutations leading to deleterious interactions with other nuclear proteins. In this work, we have elucidated the effects of 3 such mutations namely R453W, W498C and W498R on the dynamics and flexibility of the Ig-fold domain and the consequent effect on the assembly into lamina by live cell imaging, fluorescence correlation spectroscopy (FCS) and molecular dynamics (MD) simulations. From our experimental observations, we concluded that R453W has somewhat increased flexibility compared to the other mutants but lower than that of the wild type. This might be attributed due to an alteration of the salt bridges in the Ig fold domain of the mutant. This is the first report where such an alteration in the full length has been documented by gross changes in diffusional properties as a sequel to a mutation in the Ig fold domain

biochemistry↗

bioRxiv2021

Elongation factor ELOF1 drives transcription-coupled repair and prevents genome instability

Correct transcription is crucial for life. However, DNA damage severely impedes elongating RNA Polymerase II (Pol II), causing transcription inhibition and transcription-replication conflicts. Cells are equipped with intricate mechanisms to counteract the severe consequence of these transcription-blocking lesions (TBLs). However, the exact mechanism and factors involved remain largely unknown. Here, using a genome-wide CRISPR/cas9 screen, we identified elongation factor ELOF1 as an important new factor in the transcription stress response upon DNA damage. We show that ELOF1 has an evolutionary conserved role in Transcription-Coupled Nucleotide Excision Repair (TC-NER), where it promotes recruitment of the TC-NER factors UVSSA and TFIIH to efficiently repair TBLs and resume transcription. Additionally, ELOF1 modulates transcription to protect cells from transcription-mediated replication stress, thereby preserving genome stability. Thus, ELOF1 protects the transcription machinery from DNA damage by two distinct mechanisms.

cell biology↗

bioRxiv2021

Active microrheology using pulsed optical tweezers to probe viscoelasticity of Lamin A towards diagnosis of laminopathies

Lamins are nucleoskeletal proteins of mammalian cells that stabilize the structure and maintain the rigidity of the nucleus. These type V intermediate filament proteins which are predominantly of A and B types provide necessary tensile strength to the nucleus. Single amino acid missense mutations occurring all over the lamin A protein form a cluster of human diseases termed as laminopathies, a few of which principally affect the muscle and cardiac tissues responsible for load bearing functionalities of the body. One such mutation is lamin A350P which causes dilated cardiomyopathy in patients. It is likely that a change from alanine to proline in the -helical 2B rod domain of the protein might severely disrupt the propensity of the filaments to polymerise into functional higher order structures required to form a fully functional lamina with its characteristic elasticity. In this study, we validate for the very first time, the application of active microrheology employing oscillating optical tweezers to investigate any alterations in the visco-elastic parameters of the mutant protein meshwork in vitro, which might translate into possible changes in nuclear plasticity. We confirm our findings from this robust yet fast method by imaging both the wild type and mutant lamins using a super resolution microscope, and observe changes in the mesh size which explain our measured changes in the viscoelastic parameters of the lamins. This method could naturally be extended to conduct microrheological measurements on any intermediate filament protein or any protein endowed with elastic behavior, with minor schematic modifications, thus bearing significant implications in laminopathies and other diseases which are associated with changes in structural rigidity of any cellular organelle. SignificanceLamin A mutations produce an array of diseases termed as laminopathies which are primarily characterized by alteration of elastic behavior of the nucleus which in turn leads to defects in mechanotransduction. This is the first report in the lamin arena which shows a fast, accurate and direct quantification of elastic moduli of lamin A using optical tweezers-based microrheology. This has very significant implications and can be registered to be a robust and universal method that could also be suitably used for probing changes in elastic properties of any proteins or surfactants in a disease scenario such as SARS-Cov2 (Covid-19), which is pandemic at this time.

biophysics↗

bioRxiv2020

SMARCAD1 Mediated Active Replication Fork Stability Maintains Genome Integrity

Stalled fork protection pathway mediated by BRCA1/2 proteins is critical for replication fork stability that has implications in tumorigenesis. However, it is unclear if additional mechanisms are required to maintain replication fork stability. We describe a novel mechanism by which the chromatin remodeler SMARCAD1 stabilizes active replication forks that is essential for resistance towards replication poisons. We find that loss of SMARCAD1 results in toxic enrichment of 53BP1 at replication forks which mediates untimely dissociation of PCNA via the PCNA-unloader, ATAD5. Faster dissociation of PCNA causes frequent fork stalling, inefficient fork restart and accumulation of single-stranded DNA resulting in genome instability. Although, loss of 53BP1 in SMARCAD1 mutants restore PCNA levels, fork restart efficiency, genome stability and tolerance to replication poisons; this requires BRCA1 mediated fork protection. Interestingly, fork protection challenged BRCA1-deficient naive- or PARPi-resistant tumors require SMARCAD1 mediated active fork stabilization to maintain unperturbed fork progression and cellular proliferation.

cell biology↗