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Genome-Wide Profiling of Histone Modifications in Fission Yeast Using CUT&Tag.

Eukaryotic DNA is organized in the nucleus in the form of chromatin. Nucleosomes, the fundamental unit of chromatin, are subject to many posttranslational modifications (PTMs) as well as compositional variations through incorporation of histone variants. These alterations play important roles in regulation of genome structure and activity. Genome-wide profiling of these regulatory features is essential for understanding of genome function. Chromatin immunoprecipitation coupled with next-generation sequencing (ChIP-Seq) is a widely used method to assay genome-wide localization in fission yeast but suffers from the requirement for a large amount of input chromatin, antibodies, and a cumbersome experimental pipeline. New methods such as Cleavage Under Targets and Tagmentation (CUT&Tag), which combine the specificity of targeted cleavage and adapter insertion with the sensitivity of next-generation sequencing, enable identification and characterization of various epigenetic marks affording low input requirement as well as more streamlined protocols. However, these approaches have not been adapted for use in fission yeast, Schizosaccharomyces pombe. Here, we describe an adapted CUT&Tag protocol for epigenomic profiling in fission yeast using the heterochromatin-associated histone H3K9 methylation PTM for benchmarking.

Schizosaccharomyces

Write and Read: Harnessing Synthetic DNA Modifications for Nanopore Sequencing.

An exciting feature of nanopore sequencing is its ability to record multi-omic information on the same sequenced DNA molecule. Well-trained models allow the detection of nucleotide-specific molecular signatures through changes in ionic current as DNA molecules translocate through the nanopore. Thus, naturally occurring DNA modifications, such as DNA methylation and hydroxymethylation, may be recorded simultaneously with the genetic sequence. Additional genomic information, such as chromatin state or the locations of bound transcription factors, may also be recorded if their locations are chemically encoded into the DNA. Here, we present a versatile "write-and-read" framework, where chemo-enzymatic DNA labeling with unnatural synthetic tags results in predictable electrical fingerprints in nanopore sequencing. As a proof-of-concept, we explore a DNA glucosylation approach that selectively modifies 5-hydroxymethylcytosine (5hmC) with glucose or glucose-azide adducts. We demonstrate that these modifications generate distinct and reproducible electrical shifts, enabling the direct detection of chemically altered nucleotides. We further demonstrate that enzymatic alkylation, such as the enzymatic transfer of azide residues to the N6 position of adenines, also produces characteristic nanopore signal shifts relative to the native adenine and 6-methyladenine. Beyond direct nucleotide detection, this approach introduces new possibilities for bio-orthogonal DNA labeling, enabling an extended alphabet of sequence-specific detectable moieties. The future use of programmable chemical modifications for simultaneous analysis of multiple omics features on individual molecules opens new avenues for genetic research and discovery.

5-hydroxymethylcytosine (5hmC)

DNA Methylation Analysis by Bisulfite Pyrosequencing of Mouse Embryonic Fibroblasts with Reprogramming Enhanced by Thyroid Hormones.

DNA methylation is a widely studied epigenetic mark which in mammals involves the incorporation of a methyl group to the fifth carbon of cytosines, mainly those belonging to CpG dinucleotides. It has been linked to context-dependent regulatory functions ranging from gene and repetitive DNA silencing to gene body transcriptional activity. Because of its important roles during embryonic development and cell differentiation, DNA methylation can be used to track cell reprogramming by measuring the methylation levels of pluripotency-associated factors. In this scenario, bisulfite pyrosequencing is a simple, robust, and widely used technique which allows for the quantification of DNA methylation levels at small, specific regions of the genome. It involves the amplification and biotin tagging of bisulfite-converted DNA. Single amplified strands are then purified using streptavidin and finally pyrosequenced using a sequencing primer. Thus, it is an ideal method for the quantitative profiling of specific genomic regions, with applications ranging from biomarker discovery and epigenetic clock tracking to omic validation studies.

Animals

Generation of Hoxa11-3XFLAG and Hoxd11-3XFLAG alleles to investigate Hox11 genome-wide binding.

Hox genes encode for evolutionary conserved transcription factors that direct the proper development of the body plan. Despite decades of research, little is known regarding their downstream target genes, especially in vertebrates. The strong evolutionary conservation of their DNA-binding homeodomain, their generic AT-rich binding sites, and the lack of specific antibodies has precluded rigorous examination. To circumvent these limitations, we have generated two mouse models in which a 3XFLAG epitope tag has been inserted into the 5' end of the coding sequence of both Hoxa11 and Hoxd11 loci via Cas9/CRISPR. The alleles have been validated by sequencing, PCR genotyping, western blotting, and protein expression analyses, demonstrating proper targeting and expression. Breeding these alleles in combination produces viable and fertile Hoxa11FLAG/FLAG; Hoxd11FLAG/FLAG animals, with no overt patterning defects unlike Hoxa11/Hoxd11 mutants that are infertile and have severe kidney and limb defects. By performing CUT&RUN and CUT&Tag analyses, we have confirmed DNA binding to a known Six2 enhancer in the developing kidney. These novel alleles will allow characterization of the genome-wide binding profile of Hox11 proteins in vivo.

Animals

PATTY corrects open chromatin bias for improved bulk and single-cell CUT&Tag profiling.

Precise profiling of epigenomes is essential for better understanding chromatin biology and gene regulation. Cleavage Under Targets & Tagmentation (CUT&Tag) is an efficient epigenomic profiling technique that can be performed on a low number of cells and at the single-cell level. With its growing adoption, CUT&Tag datasets spanning diverse biological systems are rapidly accumulating in the field. CUT&Tag assays use the hyperactive transposase Tn5 for DNA tagmentation. Tn5's preference toward accessible chromatin alters CUT&Tag sequence read distributions in the genome and introduces open chromatin bias that can confound downstream analysis, an issue more substantial in sparse single-cell data. We show that open chromatin bias extensively exists in published CUT&Tag datasets, including those generated with recently optimized high-salt protocols. To address this challenge, we present PATTY (Propensity Analyzer for Tn5 Transposase Yielded bias), a comprehensive computational method that corrects open chromatin bias in CUT&Tag data by leveraging accompanying ATAC-seq. By integrating transcriptomic and epigenomic data using machine learning and integrative modeling, we demonstrate that PATTY enables accurate and robust detection of occupancy sites for both active and repressive histone modifications, including H3K27ac, H3K27me3, and H3K9me3, with experimental validation. We further develop a single-cell CUT&Tag analysis framework built on PATTY and show improved cell clustering when using bias-corrected single-cell CUT&Tag data compared to using uncorrected data. Beyond CUT&Tag, PATTY sets a foundation for further development of bias correction methods for improving data analysis for all Tn5-based high-throughput assays.

Journal Article

PATTY corrects open-chromatin bias for improved bulk and single-cell CUT&Tag profiling.

Precise profiling of epigenomes is essential for better understanding chromatin biology and gene regulation. Cleavage Under Targets & Tagmentation (CUT&Tag) is an efficient epigenomic profiling technique that can be performed on a low number of cells and at the single-cell level. With its growing adoption, CUT&Tag datasets spanning diverse biological systems are rapidly accumulating in the field. CUT&Tag assays use the hyperactive transposase Tn5 for DNA tagmentation. Tn5's preference toward accessible chromatin alters CUT&Tag sequence read distributions in the genome and introduces open-chromatin bias that can confound downstream analysis, an issue more substantial in sparse single-cell data. We show that open-chromatin bias extensively exists in published CUT&Tag datasets, including those generated with recently optimized high-salt protocols. To address this challenge, we present PATTY (Propensity Analyzer for Tn5 Transposase Yielded bias), a comprehensive computational method that corrects open-chromatin bias in CUT&Tag data by leveraging accompanying ATAC-seq. By integrating transcriptomic and epigenomic data using machine learning and integrative modeling, we demonstrate that PATTY enables accurate and robust detection of occupancy sites for both active and repressive histone modifications, including H3K27ac, H3K27me3, and H3K9me3, with experimental validation. We further develop a single-cell CUT&Tag analysis framework built on PATTY and show improved cell clustering when using bias-corrected single-cell CUT&Tag data compared to using uncorrected data. Beyond CUT&Tag, PATTY sets a foundation for further development of bias correction methods for improving data analysis for all Tn5-based high-throughput assays.

Journal Article

A novel DNA-protective function of Escherichia coli thioredoxin 2 mediated by its N-terminal zinc-binding domain.

Thioredoxins are ubiquitous thiol-disulfide oxidoreductases that maintain intracellular redox homeostasis. In addition to its conserved catalytic domain, Escherichia coli thioredoxin 2 (EcTrx2) possesses a unique N-terminal zinc-binding domain whose physiological function remains largely unknown. Here, we identify a previously unrecognized DNA-binding activity of EcTrx2 and demonstrate its role in protecting DNA during oxidative stress. Electrophoretic mobility shift assays showed that EcTrx2 bound plasmid DNA in a concentration-dependent and GST-tag-independent manner, whereas EcTrx1 exhibited no detectable DNA-binding activity. DNA binding was abolished by deletion of the N-terminal zinc-binding domain and was blocked by zinc occupancy, indicating that this unique domain is essential for DNA interaction. Consistent with these findings, EcTrx2 significantly protected plasmid DNA from DNase I digestion and hydroxyl radical-mediated oxidative damage in vitro. Furthermore, EcTrx2 enhanced bacterial tolerance to the DNA-damaging agents zeocin and diamide, supporting the physiological relevance of its DNA-binding activity. Our results reveal a DNA-binding role for EcTrx2 and identify its N-terminal zinc-binding domain as a key determinant of DNA binding and protection against oxidative DNA damage.

DNA binding

Whole-Genome Bisulfite Sequencing with a Small Amount of DNA.

Whole-genome bisulfite sequencing (WGBS) is the most widely used method to study DNA methylation profiles across the genome. Since the bisulfite reaction causes DNA degradation, a new approach called post-bisulfite adapter tagging (PBAT) was developed to overcome this problem by adding adapters after bisulfite treatment. In mammals, the PBAT method is used for single-cell bisulfite sequencing (scBS-seq), which enables DNA methylation analysis using a very small amount of DNA from only a few cells, including single-cell input. This protocol involves bisulfite conversion, followed by preamplification and tagging with random hexamer primers prior to Illumina library preparation. Since many procedures are completed in one single test tube, the loss of DNA can be minimized, enabling highly sensitive experiments to study DNA methylation profiles from a very small amount of input material.

Sulfites

T antigen and initiation of cell DNA synthesis in a temperature-sensitive mouse line transformed by an SV40tsA mutant and in heterokaryons of the transformed cells and chick erythrocytes.

The role of SV40 gene A product in initiation of cellular DNA synthesis was investigated, using a mouse kidney line [mKSA207] transformed by SV40tsA207. mKSA207 cells were temperature sensitive for growth, lost SV40 T antigen (Tag) when incubated in low serum at 40degreeC, and accumulated Tag in the cytoplasm when fed 10% serum and incubated at the nonpermissive temperature (39.7degreeC). Following serum addition, the percentage of mKSA207 cells synthesizing DNA was essentially the same at nonpermissive (39.7 degrees C) and permissive temperatures (33.5degreeC). The cells entered S phase asynchronously at both temperatures, but most cells entered S within 16 h, and before Tag accumulated. mKSA207 synchronized by a double thymidine block also synthesized DNA at 39.7degreesC and entered a second S phase. Tag-depleted or Tag-synchronized mKSA207, when fused with chick erythrocytes (CE), activated CE DNA synthesis. At nonpermissive temperatures (39.7degreesC), 40% of CE nuclei in heterokaryons with Tag-depleted mKSA207 displayed 3H-thymidine--labeled nuclei 28--40 h after fusion, when only 12% of CE nuclei were Tag+. The experiments indicate that SV40 gene A product probably does not have a direct role as initiator of cellular DNA synthesis.

Animals

High-Purity Monovalent Functionalization of Carbon Nanotubes.

Single-walled carbon nanotubes (SWCNTs) show promise for probing molecular interactions at single-molecule resolution, yet generating SWCNT populations bearing a single defined functional tag remains challenging because surface functionalization is inherently stochastic. Here, we present a batch-scale strategy to produce predominantly singly tagged SWCNTs by leveraging the stochastic adsorption of single-stranded DNA (ssDNA). Specifically, SWCNTs are dispersed using a mixture of unmodified ssDNA (um-ssDNA) and a minor fraction of modified ssDNA (m-ssDNA) carrying an affinity handle. We developed a probabilistic ssDNA-SWCNT binding model that predicts the distribution of m-ssDNA per nanotube as a function of the input minor-strand fraction p = m-ssDNA/total ssDNA, enabling selection of conditions that maximize single-tag purity. Using magnetic-bead capture via a biotin affinity interaction and subsequent release, we isolate SWCNTs with 97.6% predicted single-tag purity at 2% recovery. Single-molecule fluorescence imaging further supports predominantly single-label occupancy under the model-selected conditions. Thus, this approach provides a general route to SWCNTs bearing a single molecular handle for downstream conjugation and assembly, supporting diverse future applications in SWCNT-based nanotechnologies.

Nanotubes, Carbon

prot4EST: translating expressed sequence tags from neglected genomes.

BACKGROUND: The genomes of an increasing number of species are being investigated through generation of expressed sequence tags (ESTs). However, ESTs are prone to sequencing errors and typically define incomplete transcripts, making downstream annotation difficult. Annotation would be greatly improved with robust polypeptide translations. Many current solutions for EST translation require a large number of full-length gene sequences for training purposes, a resource that is not available for the majority of EST projects. RESULTS: As part of our ongoing EST programs investigating these "neglected" genomes, we have developed a polypeptide prediction pipeline, prot4EST. It incorporates freely available software to produce final translations that are more accurate than those derived from any single method. We show that this integrated approach goes a long way to overcoming the deficit in training data. CONCLUSIONS: prot4EST provides a portable EST translation solution and can be usefully applied to >95% of EST projects to improve downstream annotation. It is freely available from http://www.nematodes.org/PartiGene.

Animals

Gene finding in the chicken genome.

BACKGROUND: Despite the continuous production of genome sequence for a number of organisms, reliable, comprehensive, and cost effective gene prediction remains problematic. This is particularly true for genomes for which there is not a large collection of known gene sequences, such as the recently published chicken genome. We used the chicken sequence to test comparative and homology-based gene-finding methods followed by experimental validation as an effective genome annotation method. RESULTS: We performed experimental evaluation by RT-PCR of three different computational gene finders, Ensembl, SGP2 and TWINSCAN, applied to the chicken genome. A Venn diagram was computed and each component of it was evaluated. The results showed that de novo comparative methods can identify up to about 700 chicken genes with no previous evidence of expression, and can correctly extend about 40% of homology-based predictions at the 5' end. CONCLUSIONS: De novo comparative gene prediction followed by experimental verification is effective at enhancing the annotation of the newly sequenced genomes provided by standard homology-based methods.

Animals

EST-SSR based genetic polymorphism among Lablab (Lablab purpureus L. Sweet) accessions contrasting for drought stress at seedling stage.

Lablab is a multipurpose and the most drought-tolerant (DT) crop compared with its relatives. Despite its potential, Lablab is still an underutilized crop with a lack of improved varieties in many countries. The DT (D349, D147, HA4, D363, D352, D359, D348, D311, D55 and D250) and drought-susceptible (DS) (D271, D66, D106, D6, D26, D255, D28, D186, D95, and D258) accessions were earlier identified according to their morphological and biochemical responses to moisture stress at the seedling stage. These accessions were used to establish genetic polymorphism among the accessions contrasting for drought stress based on the Expressed Sequence Tag-Simple Sequence Repeats (EST-SSR) markers. The CTAB protocol was employed for the genomic DNA extraction. After DNA quality and quantity verification, the PCR was conducted using 16 EST-SSR primer pairs specific to the Lablab. The products were separated through the horizontal polyacrylamide gel electrophoresis (hPAGE). Discriminating ability of the markers and primers' efficiency were evaluated based on various genetic parameters. Principal Coordinate Analysis (PCoA) was performed to estimate the distance matrix among the population and among the accessions. While cluster analysis was processed to trace the genetic relationship among the accessions, dendrogram was constructed to decipher their genetic relationship. Analysis of Molecular Variance (AMOVA) was finally computed to quantify the diversity level and genetic relationship among the population, and among the accessions. A low polymorphism (GD = 0.19) was observed between the DT and DS accessions, likely due to limited discriminatory power of the EST-SSR markers. However, the PCoA, cluster analysis and AMOVA identified DT (D147, HA4, and D349) and DS (D106, D95, and D271) accessions as strongly contrasting populations under drought stress, with D147, HA4, D349, D363, D359, D352, and D348 further recommended as DT accessions. Given the low polymorphism observed, further validation using more informative molecular markers and advanced genomic approaches is recommended to improve the identification of drought-tolerance genes and related QTLs to support Lablab breeding programs.

Expressed Sequence Tags

Single-molecule tracking of RNA-DNA hybrid removal enzymes important for lagging-strand replication.

The formation of RNA-DNA hybrid (RDH) primers by primase is an essential step in the recruitment of DNA polymerase during replication initiation and for the synthesis of each Okazaki fragment on the lagging strand. In addition to primers, RDHs form through misincorporation of ribonucleotides by DNA polymerase during elongation and by formation of R loops during transcription. R loops are three-stranded structures that form when the nascent mRNA anneals to the template DNA strand, displacing the complementary DNA strand. The persistence of RDHs is deleterious to genome stability in all cells because they increase susceptibility to mutations, impaired replication fork progression, DNA double-stranded breaks, and genomic rearrangements. In many bacteria, it is well established that components of the replicative DNA polymerase form a macromolecular complex that can be imaged using single-molecule or ensemble fluorescence approaches. The spatiotemporal regulation of proteins involved in RDH removal during lagging-strand maturation is less clear. Here, we study three proteins that are involved in the removal of RDHs from the lagging strand during DNA replication in the Gram-positive bacterium Bacillus subtilis: DNA polymerase I (Pol I), FenA, and RNase HIII. We characterized the behavior of each PAmCherry-tagged lagging-strand enzyme in living cells using single-particle tracking photoactivated localization microscopy. We find that all three proteins are highly mobile, suggesting residence times at their target substrates are below our temporal resolution. We also find evidence that Pol I activity is modulated through interaction with the replisome, whereas FenA and RNase HIII are regulated through access to the nucleoid. Our results provide new insight into how enzymes are recruited to resolve RDHs during lagging-strand replication in vivo.

DNA Replication

Fidelity of replication of phage phi X174 DNA by DNA polymerase III holoenzyme: spontaneous mutation by misincorporation.

DNA from phi X174 is replicated in vitro with a fidelity similar to that found genetically. A mutation of TAG leads to TGG may be induced, however, by varying the concentrations of deoxynucleoside triphosphates, with a frequency proportional to [dGTP]2/[dATP]. This complex concentration dependence is consistent with the active participation of a proofreading mechanism that hydrolytically excises mismatched base pairs as they are formed. A simple kinetic analysis predicts that the frequency of misincorporation depends on the ratio of incorrect to correct deoxynucleoside triphosphates times the concentration of the next triphosphate in the sequence to be added. This suggests that spontaneous mutation by misincorporation depends crucially on the composition of the deoxynucleoside triphosphate pool.

Bacteriophage phi X 174

AML1-ETO hijacks a distal enhancer of NAT10 to reprogram glutathione metabolism and sustain leukemia stem cell stemness.

Chromosomal translocations produce oncogenic fusion proteins such as AML1-ETO, which predominantly occupy gene promoters to induce transcriptional reprogramming in leukemia stem cells (LSCs), consequently driving the pathogenesis of t(8;21) acute myeloid leukemia (AML). However, whether AML1-ETO is recruited to additional regulatory DNA elements to orchestrate oncogenic gene expression programs has not been fully addressed. Here, we define AML1-ETO and H3K27ac CUT&Tag landscapes in primary t(8;21) AML CD34+ cells and t(8;21) AML cell lines, revealing AML1-ETO binding at a distal enhancer of the RNA N4-acetylcytidine (ac4C) writer N-acetyltransferase 10 (NAT10), thereby driving its transcriptional activation. Genetic ablation or pharmacological inhibition of NAT10 restricted the survival and self-renewal of LSCs in primary t(8;21) AML CD34+ cells, as well as in a retroviral AML1-ETO9a-driven t(8;21) AML mouse model, establishing NAT10 as a potential therapeutic vulnerability. Mechanistically, NAT10 is recruited to glutathione S-transferase omega 2 (GSTO2) mRNA to catalyze ac4C modification, thereby enhancing transcript stability and reprogramming glutathione metabolism, as demonstrated by ac4C profiling, RNA immunoprecipitation (RIP), and dCas13b-NAT10-based analyses. Silencing of GSTO2 in primary t(8;21) AML CD34+ cells decreased intracellular reduced glutathione (GSH) levels and compromised LSC survival and self-renewal, whereas GSTO2 overexpression or GSH supplementation largely rescued LSC maintenance following NAT10 loss. Collectively, these findings enrich and extend the understanding of AML1-ETO regulatory programs by linking distal enhancer activity to a NAT10-GSTO2 ac4C-GSH axis that integrates epigenomic, posttranscriptional, and metabolic reprogramming to sustain LSC stemness, highlighting this circuit as a potential therapeutic vulnerability in t(8;21) AML.

Humans

Gene Cloning, Expression, and Purification of Kunitz Trypsin Inhibitor from Glycine max Using Halo Tag.

Soybean Kunitz Trypsin Inhibitor (SKTI) is one of the most extensively studied protease inhibitors, with applications in pest management, medicine, the food processing industry, and the leather industry. In this study, SKTI was cloned into the pFN29A Flexi vector containing a barnase gene. Genomic DNA was isolated from tender soybean leaves, and SKTI was amplified by PCR to obtain a 671 bp product. After cloning, an internal 380 bp sequence was amplified using specific primers to confirm that the cloned sequence was a functional SKTI, as non-functional SKTI genes also exist in Glycine max. The amplified PCR product, containing an AsiSI site at the 5' end and a PmeI site at the 3' end, was cloned into the pFN29A vector. The resulting colonies were screened by colony PCR, and the insert sequence was confirmed by Sanger sequencing. The recombinant protein, containing a His-tag, Halo-tag, and a TEV protease cleavage site, was expressed in Escherichia coli BL21 cells. Maximum expression was achieved 5 h after induction with 0.5 mM IPTG at 37 °C. The expressed SKTI was purified using affinity chromatography on HaloLink resin, and the bound SKTI was cleaved with HaloTEV protease to obtain pure SKTI. The purified inhibitor effectively inhibited bovine trypsin, with an IC₅₀ of 0.6 ± 0.003 µg/µl, yielding 1.6 mg per gram of bacterial pellet. The 24 kDa inhibitor remained stable up to a temperature of 50 °C. Kinetic analysis revealed that recombinant SKTI competitively inhibits trypsin, with a Kᵢ value of 14 µM.

Cloning, Molecular

Marine-Inspired Antimicrobial Peptides Disrupt Gene Expression at the DNA Level.

Genome mining of Streptomyces sp. H-KF8 combined with sequence engineering yielded two serum-stable, noncytotoxic, nonlytic antimicrobial peptides, L3 and L3-K. Initial studies in uropathogenic Escherichia coli suggested membrane effects and nucleoid relaxation, prompting a comprehensive investigation of their mode of action. In this study tandem mass tag (TMT)-based quantitative proteomics revealed extensive proteome remodeling, with 175 and 120 differentially expressed proteins (DEPs) after treatment with L3 and L3-K, respectively. L3 induced predominantly upregulated responses linked to metabolism, RNA processing, transport, and homeostasis, whereas L3-K mainly caused the downregulation of proteins involved in metabolism, transport, and cell structure. Both peptides disrupted ABC transporter-mediated nutrient uptake and elicited stress responses, while L3 specifically perturbed the mal regulon, indicative of broader transcriptional dysregulation. Complementary fluorescent dye displacement and in vitro transcription/translation assays demonstrated nonspecific DNA binding, stronger for L3 than L3-K, and potent inhibition of transcriptional and translational processes. Strikingly, inhibitory concentrations paralleled their minimum inhibitory concentrations, directly linking DNA binding and interference with central information processing to antimicrobial activity. These findings reveal that L3 and L3-K primarily act by targeting DNA and interfering with the transcription-translation machinery. Beyond offering mechanistic insights, this study underscores peptides' potential to act as scaffolds for next-generation antimicrobial peptides with DNA-binding and nonmembrane-lytic activity.

Antimicrobial Peptides