Biology subjects

Phan, N. T.

Publications and source records attributed to Phan, N. T..

9 recordsLinked to original sources

bioRxiv2026

RNA m6A mediates de novo DNA methylation and heritable epigenetic silencing in human cells

DNA methylation is the most abundant epigenetic modification on the human genome and changes dynamically during embryogenesis, aging, and disease. How DNA methylation is established de novo remains incompletely understood. Using orthogonal CRISPR platforms to initiate de novo DNA methylation coupled with genome-wide CRISPR screens and proximity-dependent proteomics, we discover the interplay between RNA m6A modifications and de novo DNA methylation to program heritable epigenetic memory in human cells. The RNA m6A writer complex is recruited to chromatin with DNA methyltransferases and histone repressors during the transient establishment phase of heritable epigenetic silencing. Inhibition of RNA m6A during early pluripotent transition leads to defects in de novo DNA methylation, resulting in upregulation of transposable elements that pose a threat to genome integrity during early development. Our work reveals the vital coordination between the epitranscriptome and de novo DNA methylation to establish proper heritable epigenetic silencing in human cells.

genetics↗

bioRxiv2026

An omega glutathione S-transferase in Apis mellifera contributes to chemical adaptation through pesticide sequestration and antioxidant defense

The European honey bee (Apis mellifera L.) is a key agricultural pollinator frequently exposed to pesticide residues, yet the molecular basis of its chemical adaptation, particularly glutathione S-transferases (GSTs) involved in xenobiotic detoxification, remain incompletely understood. In this study, AmGSTO1 was structurally and functionally characterized to evaluate its role in agrochemical interaction and protection against oxidative stress. The crystal structure of AmGSTO1 in complex with glutathione revealed its 3D architecture and key active-site residues were identified by structural analysis and site-directed mutagenesis. Fluorescence binding assays demonstrated measurable affinity for multiple agrochemicals, including TCP, fenoprop, 2,4-D, tetramethrin, nicotine, and 3-phenoxybenzaldehyde. However, HPLC analysis showed no detectable substrate depletion, suggesting ligand binding to AmGSTO1 without catalytic turnover. AmGSTO1 exhibited antioxidant activity toward cumene hydroperoxide, hydrogen peroxide, and paraquat, as well as dehydroascorbate reductase activity. These findings indicate that AmGSTO1 may contribute to agrochemical tolerance through ligand sequestration and redox protection mechanisms.

biochemistry↗

bioRxiv2026

LEMONmethyl-seq: Targeted long-read DNA methylation profiling reveals dynamics of CRISPR epigenome editing and endogenous DNA methylation patterns

BACKGROUNDDNA methylation is the most prevalent epigenetic modification in human cells and undergoes dynamic changes during cell differentiation, disease progression, and aging. Here, we introduce Locus-Enriched Mapping Of Nucleotide methylation (LEMONmethyl-seq): an optimized, cost-effective pipeline for single-nucleotide detection of DNA methylation using locus-specific amplification and long-read DNA sequencing. RESULTSWe apply LEMONmethyl-seq to profile DNA methylation of endogenous gene promoters across different cell types along with DNA methylation establishment and long-range propagation induced by CRISPR epigenome editing technologies. We profile dynamic changes in DNA methylation patterns on transposable element genomic loci during global epigenetic resetting in stem cells, and we identify site-specific enrichment of non-canonical CpH methylation on genomic sites in stem cells and cultured neurons. Lastly, we apply LEMONmethyl-seq to profile DNA methylation across the MGMT promoter, a clinical biomarker for glioblastoma. We identify additional differentially methylated sites correlated with chemotherapeutic sensitivity, which may be clinically relevant. CONCLUSIONSTogether, LEMONmethyl-seq serves as a cost-effective, long-read DNA methylation sequencing pipeline that advances methods for detecting DNA methylation patterns and dynamics in mammalian cells. We envision its broad use for studying chromatin pathways, diagnostics, and therapeutic applications.

molecular biology↗

bioRxiv2026

A toolkit for programmable transcriptional engineering across eukaryotic kingdoms

Chromatin is essential for eukaryotic life. Tens of thousands of chromatin regulator (CR) proteins exist in eukaryotic genomes that are predicted to modulate chromatin states; however, their molecular functions remain largely untested experimentally. Here, we construct a library of over 300 full-length CRs from humans, plants, yeast, protozoa, and virus, each fused to DNA-binding domains, and test their direct effect on transcriptional repression and activation in plants and human cells. We discover CRs with cross-kingdom functionality when transferred across eukaryotes, including CRs that outperform existing tools for programmable transcriptional repression and activation in plants and human cells. Using pooled CRISPR screens, we demonstrate a suite of CRISPR repressors that titrate gene expression at intermediate levels. Finally, we identify RCOR1 and MTA2 as universal eukaryotic repressors that retain repressive activity in plants, yeast, and human cells. Our toolkit advances synthetic eukaryotic engineering and expands our understanding of CR functionality across eukaryotes.

synthetic biology↗

bioRxiv2023

Contribution of the delta-class glutathione S-transferase to agrochemical adaptation in Apis mellifera

The European honey bee, Apis mellifera, serves as the principle managed pollinator species globally. In recent decades, honey bee populations have been facing serious health threats from combined biotic and abiotic stressors, including diseases, limited nutrition, and agrochemical exposure. Understanding the molecular mechanisms underlying xenobiotic adaptation of A. mellifera is critical, considering its extensive exposure to phytochemicals and agrochemicals present in flowers, propolis, hives, and the environment. In this study, we conducted a comprehensive structural and functional characterization of AmGSTD1, a delta class glutathione S-transferase (GST) enzyme, to unravel its roles in agrochemical detoxification and antioxidative stress responses. Significantly, we determined the 3D structure of a honey bee GST using protein crystallography for the first time, providing new insights into its molecular structure. Our investigations revealed that AmGSTD1 efficiently metabolizes model substrates, including 1-chloro-2,4-dinitrobenzene (CDNB), p-nitrophenyl acetate (PNA), phenylethyl isothiocyanate (PEITC), propyl isothiocyanate (PITC), and the oxidation byproduct 4-hydroxynonenal (4-HNE). Moreover, we discovered that AmGSTD1 exhibits binding affinity with the fluorophore 8-Anilinonaphthalene-1-sulfonic acid (ANS), which can be inhibited with various herbicides, fungicides, insecticides, and their metabolites. These findings highlight the potential contribution of AmGSTD1 in safeguarding honey bee health against various agrochemicals and their metabolites, while also mitigating oxidative stress resulting from exposure to these substances.

pharmacology and toxicology↗

bioRxiv2022

Systemic pesticides in a solitary bee pollen food store affect larval development and increase pupal mortality

Solitary bees are often exposed to various pesticides applied for pest control on farmland while providing pollination services to food crops1. Increasing evidence suggests that sublethal toxicity of agricultural pesticides affects solitary bees differently than the social bees used to determine regulatory thresholds like honey bees and bumblebees2-4. Studies on solitary bees are challenging because of the difficulties in obtaining large numbers of eggs or young larvae for bioassays. Here we show the toxic and sublethal developmental effects of four widely used plant systemic pesticides on the Japanese orchard bee (Osmia cornifrons). Pollen food stores of this solitary bee were treated with different concentrations of three insecticides (acetamiprid, flonicamid, and sulfoxaflor) and a fungicide (dodine). Eggs were transplanted to the treated pollen and larvae were allowed to feed on the pollen stores after egg hatch. The effects of chronic ingestion of contaminated pollen were measured until adult eclosion. This year-long study revealed that chronic exposure to all tested pesticides delayed larval development and lowered larval and adult body weights. Additionally, exposure to the systemic fungicide resulted in abnormal larval defecation and increased mortality at the pupal stage, indicating potential risk to bees from fungicide exposure. These findings demonstrate potential threats to solitary bees from systemic insecticides and fungicides and will help making policy decisions for mitigating these effects.

ecology↗

bioRxiv2021

Electrochemical measurements reveal reactive oxygen species in stress granules.

Stress granules (SGs) are membraneless organelles that assemble in the cytoplasm to organize cellular contents and promote rapid adaptation during stress. To understand how SGs contribute to physiological functions, we used electrochemical measurements to detect electroactive species in SGs. With amperometry, we discovered that reactive oxygen species (ROS) are encapsulated inside arseniteinduced SGs, and H2O2 is the main species. The release kinetics of H2O2 from single SGs and the number of H2O2 molecules were quantified. The discovery that SGs contain ROS implicates them as communicators of the cellular stresses rather than a simple end-point. This may explain how SGs regulate cellular metabolism and stress responses. This may also help better understand their cytoprotective functions in pathological conditions associated with SGs such as neurodegenerative diseases, cancers and viral infections.

biochemistry↗

bioRxiv2020

White matter integrity requires continuous myelin synthesis at the inner tongue

Myelin, the electrically insulating axonal sheath, is composed of lipids and proteins with exceptionally long lifetime. This raises the question how myelin function is affected by myelin turnover. We have studied the integrity of myelinated tracts after experimentally preventing the formation of new myelin in the CNS of adult mice, using an inducible Mbp null allele. Oligodendrocytes survived recombination, continued expressing myelin genes, but failed to maintain compacted myelin sheaths. Using 3D electron microscopy and mass spectrometry imaging we visualized myelin-like membranes that failed to incorporate adaxonally, most prominently at juxta-paranodes. Myelinoid body formation indicated degradation of existing myelin at the abaxonal side and at the inner tongue of the sheath. Compacted myelin thinning and shortening of internodes, with about 50% myelin lost after 20 weeks (=5 months), ultimately led to axonal pathology and neurological disease. These data reveal that functional axon-myelin units require the continuous incorporation of new myelin membranes.

neuroscience↗

bioRxiv2020

Mass Spectrometry Imaging of Cocaine, Drug Removal and Methylphenidate AlterPhospholipids in Drosophila Brain

Cocaine dependence displays a broad impairment in cognitive performance including attention, learning and memory. To obtain a better understanding of the action of cocaine in the nervous system, and the relation between phospholipids and memory, we have investigated whether phospholipids recover in the brain following cocaine removal using the fly model, Drosophila. In addition, the effects of methylphenidate, a substitute medication for cocaine dependence, on fly brain lipids after cocaine abuse are also determined to see if it can rescue the lipid changes caused by cocaine. Time of flight secondary ion mass spectrometry with a (CO2)6000+ gas cluster ion beam was used to detect intact phospholipids. We show that cocaine has persistent effects, both increasing and decreasing the levels of specific phosphatidylethanolamines and phosphatidylinositols. These changes remain after cocaine withdrawal and are not rescued by methylphenidate. Cocaine is again shown to generally increase the levels of phosphatidylcholines in the fly brain; however, after drug withdrawal the abundance of these lipids returns to the original level and methylphenidate treatment of the flies following cocaine exposure enhances the reversal of the lipid level reducing them below the original control. The study provides insight into the molecular effects of cocaine and methylphenidate on brain lipids. We suggest that phosphatidylcholine could be a potential target for the treatment of cocaine abuse, as well as be a significant hallmark of cognition and memory loss with cocaine.

neuroscience↗