Biology subjects

Ram-Mohan, N.

Publications and source records attributed to Ram-Mohan, N..

10 recordsLinked to original sources

bioRxiv2026

Z-DNA is an Intrinsic Structural Component of Neutrophil Extracellular Traps

Neutrophil extracellular traps (NETs), with their networked extracellular DNA (eDNA), are key effectors of innate immunity which when ineffectively cleared can lead to immunopathologies. Here, we demonstrate the existence of intrinsic, host-derived left-handed noncanonical Z-DNA in NETs eDNA. Immunofluorescence staining of NETs formed in response to diverse NETosis pathways resulted in extensive filamentous Z-DNA tracing the non-Z-DNA backbone irrespective of the stimulus suggesting converging mechanisms. Circular dichroism validated the existence of Z-DNA in NETs. Temporal analysis revealed Z-DNA formation through a staged process sourced from early mitochondrial DNA release engaging with ZBP1 and transitioning to nuclear-derived as NETs mature, increasing through nucleation of new domains, revealing a heterogeneous and dynamically evolving B-to-Z-DNA landscape. The intrinsic Z-DNA showed greater relative retention than its non-Z-DNA counterpart following nuclease treatment. Modulation of DNA structure using chloroquine induced Z-to-B transition and restored susceptibility to nuclease-mediated degradation thereby establishing conformation as a tunable determinant of NET architecture. Critically, Z-DNA-enriched NETs induce significantly greater IFN- from PBMCs compared to non-Z-DNA fractions, linking NETs Z-DNA to innate immune activation. NETs may also represent endogenous antigens for anti-Z-DNA antibodies, and Z-DNA may contribute as an additional intrinsic structural determinant of NET persistence observed in DNase-rich vasculature.

immunology↗

bioRxiv2023

Neutrophil Extracellular Traps have DNAzyme activity that drives bactericidal potential

The mechanisms of bacterial killing by neutrophil extracellular traps (NETs) are unclear. DNA, the largest component of NETs is believed to merely be a scaffold with minimal antimicrobial activity through the charge of the backbone. Here, we report that NETs DNA is beyond a scaffold and produces hydroxyl free radicals through the spatially concentrated G-quadruplex/hemin DNAzyme complexes, driving bactericidal effects. Immunofluorescence staining showed colocalization of G-quadruplex and hemin in extruded NETs DNA, and Amplex UltraRed assay portrayed its peroxidase activity. Proximity labeling of bacteria revealed localized concentration of radicals resulting from NETs bacterial trapping. Ex vivo bactericidal assays revealed that G-quadruplex/hemin DNAzyme is the primary driver of bactericidal activity in NETs. NETs are DNAzymes that may have important biological consequences. One-Sentence SummaryG-quadruplex/hemin DNAzymes may be major contributors to biological consequences of neutrophil extracellular traps.

immunology↗

bioRxiv2023

Rapid molecular phenotypic antimicrobial susceptibility test for Neisseria gonorrhoeae based on propidium monoazide viability PCR

Neisseria gonorrhoeae (NG) is an urgent threat to antimicrobial resistance (AMR) worldwide. NG has acquired rapid resistance to all previously recommended treatments leaving ceftriaxone monotherapy as the first and last line of therapy for uncomplicated NG. The ability to rapidly determine susceptibility, which is currently nonexistent for NG, has been proposed as a strategy to preserve ceftriaxone by using alternative treatments. Herein, we used a DNA-intercalating dye in combination with NG-specific primers/probes to generate qPCR cycle threshold (Ct) values at different concentrations of 2 NG-relevant antimicrobials. Our proof of concept dual-antimicrobial logistic regression model based on the differential Ct measurements achieved an AUC of 0.93 with a categorical agreement for susceptibility of 84.6%. When surveying the performance against each antimicrobial separately, the model predicted 90% and 75% susceptible and resistant strains respectively to ceftriaxone and 66.7% and 83.3% susceptible and resistant strains respectively to ciprofloxacin. We further validated the model against the individual replicates and determined the accuracy of the model in classifying susceptibility agnostic of the inoculum size. We demonstrated a novel PCR-based approach to determine phenotypic ciprofloxacin and ceftriaxone susceptibility information for NG with reasonable accuracy in under 30 min, a significant improvement compared to the conventional method which takes 3 days. Table of Content Graphic O_FIG_DISPLAY_L [Figure 1] M_FIG_DISPLAY C_FIG_DISPLAY

microbiology↗

bioRxiv2022

The circulating phageome reflects bacterial infections

Bacteriophage, viruses that infect bacteria, are abundant in the human body but the relationship between the phageome and bacterial population dynamics is unclear. Because bacteriophage are often highly specific to bacterial host strains and species, we asked whether bacteriophage present in cell-free DNA (cfDNA) reflect bacterial infections in sepsis. To address this, we generated a workflow for identifying and interpreting bacteriophage sequences in cfDNA and a bacteriophage characteristic dictionary. In two independent cohorts of infected patients and asymptomatic controls, we demonstrate that all individuals, septic and healthy, have a circulating phageome. Moreover, infection associates with overrepresentation of pathogen-specific phage, allowing for the study of bacterial pathogens. We further show that phage can identify pathovariant Escherichia coli infections and distinguish between closely-related pathogenic bacterial species such as Staphylococcus aureus and frequent contaminants such as coagulase-negative Staphylococcus. Phage DNA may have utility in studying bacteriophage ecology in infection.

microbiology↗

bioRxiv2022

Disease diagnostics using machine learning of immune receptors

Clinical diagnosis typically incorporates physical examination, patient history, and various laboratory tests and imaging studies, but makes limited use of the human systems own record of antigen exposures encoded by receptors on B cells and T cells. We analyzed immune receptor datasets from 593 individuals to develop MAchine Learning for Immunological Diagnosis (Mal-ID), an interpretive framework to screen for multiple illnesses simultaneously or precisely test for one condition. This approach detects specific infections, autoimmune disorders, vaccine responses, and disease severity differences. Human-interpretable features of the model recapitulate known immune responses to SARS-CoV-2, Influenza, and HIV, highlight antigen-specific receptors, and reveal distinct characteristics of Systemic Lupus Erythematosus and Type-1 Diabetes autoreactivity. This analysis framework has broad potential for scientific and clinical interpretation of human immune responses.

immunology↗

bioRxiv2020

Insights into gene expression changes under conditions that facilitate horizontal gene transfer (mating) of a model Archaeon

Horizontal gene transfer is a means by which bacteria, archaea, and eukaryotes are able to trade DNA within and between species. While there are a variety of mechanisms through which this genetic exchange can take place, one means prevalent in the archaeon Haloferax volcanii involves the transient formation of cytoplasmic bridges between cells and is referred to as mating. This process can result in the exchange of very large fragments of DNA between the participating cells. Genes governing the process of mating, including triggers to initiate mating, mechanisms of cell fusion, and DNA exchange, have yet to be characterized. We used a transcriptomic approach to gain a more detailed knowledge of how mating might transpire. By examining the differential expression of genes expressed in cells harvested from mating conditions on a filter over time and comparing them to those expressed in a shaking culture, we were able to identify genes and pathways potentially associated with mating. These analyses provide new insights into both the mechanisms and barriers of mating in Hfx. volcanii.

microbiology↗

bioRxiv2020

A novel platform to accelerate antimicrobial susceptibility testing in Neisseria gonorrhoeae using RNA signatures

The rise of antimicrobial-resistant pathogens can be attributed to the lack of a rapid pathogen identification (ID) or antimicrobial susceptibility testing (AST), resulting in delayed therapeutic decisions at the point of care. Gonorrhea is usually empirically treated with no AST results available before treatment, thus contributing to the rapid rise in drug resistance. Herein we present a rapid AST platform using RNA signatures for Neisseria gonorrhoeae (NG). RNA-seq followed by bioinformatic tools were applied to explore potential markers in the transcriptome profile of NG upon minutes of azithromycin exposure. Validation of candidate markers using PCR showed that two markers (arsR (NGO1562) and rpsO) can deliver accurate AST results across 14 tested isolates. Further validation of our cutoff in comparison to MIC across 64 more isolates confirmed the reliability of our platform. Our RNA markers combined with emerging molecular point-of-care systems has the potential to greatly accelerate both ID and AST to inform treatment.

molecular biology↗

bioRxiv2020

Integrative profiling of early host chromatin accessibility responses in human neutrophils with sensitive pathogen detection.

Sepsis is a leading cause of death globally where neutrophils respond to pathogens via tightly regulated antimicrobial effectors. Combining early neutrophilic responses and pathogen detection may reveal insights for disease recognition. We performed ATAC-seq of human neutrophils challenged with six toll-like receptor ligands and two organisms; and RNA-seq after Escherichia coli (EC) exposure for 1 and 4 hours along with ATAC-seq. ATAC-seq of neurophils retains more pathogenic DNA reads than standard library preparation methods. Only a fraction of differential chromatin regions overlap between challenges. Shared signatures exist for ligands but rest are unique in position, function, and challenge. Epigenomic changes are plastic, only [~]500 are shared by EC challenges over time, resulting in varied differential genes and associated processes. We also identify three classes of chromatin mediated gene regulation based on their relative locations. These and transcription factor footprinting reveal timely and challenge specific mechanisms of transcriptional regulation in neutrophils.

immunology↗

bioRxiv2019

Regulatory context drives conservation of glycine riboswitch aptamers

In comparison to protein coding sequences, the impact of mutation and natural selection on the sequence and function of non-coding (ncRNA) genes is not well understood. Many ncRNA genes are narrowly distributed to only a few organisms, and appear to be rapidly evolving. Compared to protein coding sequences, there are many challenges associated with assessment of ncRNAs that are not well addressed by conventional phylogenetic approaches, including: short sequence length, lack of primary sequence conservation, and the importance of secondary structure for biological function. Riboswitches are structured ncRNAs that directly interact with small molecules to regulate gene expression in bacteria. They typically consist of a ligand-binding domain (aptamer) whose folding changes drive changes in gene expression. The glycine riboswitch is among the most well-studied due to the widespread occurrence of a tandem aptamer arrangement (tandem), wherein two homologous aptamers interact with glycine and each other to regulate gene expression. However, a significant proportion of glycine riboswitches are comprised of single aptamers (singleton). Here we use graph clustering to circumvent the limitations of traditional phylogenetic analysis when studying the relationship between the tandem and singleton glycine aptamers. Graph clustering enables a broader range of pairwise comparison measures to be used to assess aptamer similarity. Using this approach, we show that one aptamer of the tandem glycine riboswitch pair is typically much more highly conserved, and that which aptamer is conserved depends on the regulated gene. Furthermore, our analysis also reveals that singleton aptamers are more similar to either the first or second tandem aptamer, again based on the regulated gene. Taken together, our findings suggest that tandem glycine riboswitches degrade into functional singletons, with the regulated gene(s) dictating which glycine-binding aptamer is conserved.\n\nAuthor SummaryThe glycine riboswitch is a ncRNA responsible for the regulation of several distinct gene sets in bacteria that is found with either one (singleton) or two (tandem) aptamers, each of which directly senses glycine. Which aptamer is more important for gene-regulation, and the functional difference between tandem and singleton aptamers, are long-standing questions in the riboswitch field. Like many biologically functional RNAs, glycine aptamers require a specific 3D folded conformation. Thus, they have low primary sequence similarity across distantly related homologs, and large changes in sequence length that make creation and analysis of accurate multiple sequence alignments challenging. To better understand the relationship between tandem and singleton aptamers, we used a graph clustering approach that allows us to compare the similarity of aptamers using metrics that measure both sequence and structure similarity. Our investigation reveals that in tandem glycine riboswitches, one aptamer is more highly conserved than the other, and which aptamer is conserved depends on what gene(s) are regulated. Moreover, we find that many singleton glycine riboswitches likely originate from tandem riboswitches in which the ligand-binding site of the non-conserved aptamer has degraded over time.

bioinformatics↗

bioRxiv2018

The Transcriptional landscape of Streptococcus pneumoniae reveals a complex operon architecture and abundant riboregulation critical for growth and virulence

Efficient and highly organized transcription initiation and termination is fundamental to an organisms ability to survive, proliferate, and quickly respond to its environment. Over the last decade, our simplistic outlook of bacterial transcriptional regulation and architecture has evolved to include stimulus-responsive regulation by untranslated RNA and the formation of alternate transcriptional units. In this study, we map the transcriptional landscape of the bacterial pathogen Streptococcus pneumoniae by applying a combination of high-throughput RNA-sequencing techniques. Our study reveals a complex transcriptome wherein environment-respondent alternate transcriptional units are observed within operons stemming from internal transcription start sites (TSS) and transcription terminators (TTS) suggesting that more fine-tuning of regulation occurs than previously thought. Additionally, we identify many putative cis-regulatory RNA elements and riboswitches within 5-untranslated regions (5-UTR) of genes. By integrating TSSs and TTSs with independently collected RNA-Seq datasets from a variety of conditions, we establish the response of these regulators to changes in growth conditions and validate several of them. Furthermore, to determine the importance of ribo-regulation by 5-UTR elements for in vivo virulence, we show that the pyrR regulatory element is essential for survival, successful colonization and infection in mice suggesting that such RNA elements are potential drug targets. Importantly, we show that our approach of combining high-throughput sequencing with in vivo experiments can reconstruct a global understanding of regulation, but also pave the way for discovery of compounds that target (ribo-) regulators to mitigate virulence and antibiotic resistance.

microbiology↗