Name: methodology for accurate detection of mitochondrial dna methylation
Uploaded: 2018-05-20T13:30:00
Description: Watch this Scientific Journal Video about Methodology for Accurate Detection of Mitochondrial DNA Methylation at JoVE.com

The Novo Nordisk Foundation Centre for Basic Metabolic Research is an independent research center at the University of Copenhagen partially funded by an unrestricted donation from the Novo Nordisk Foundation.

1. Restriction Enzyme Treatment
<ol>
	<li>Linearize mtDNA by treating total human DNA with the restriction enzyme BamHI, that cuts at position 14258 in the human mitochondrial DNA. 
	NOTE: For mouse DNA, use the restriction enzyme BglII under identical conditions as below.</li>
	<li>For each sample where mtDNA methylation is to be assessed, prepare one 0.2 mL reaction tube and add the following mix:3 &#956;g genomic DNA (quantified by fluorometry), 15 &#956;L Buffer 3, 3 &#956;L BamHI and water up to of 150 &#956;...

<ol>
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A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Amount+and+distribution+of+5-methylcytosine+in+human+DNA+from+different+types+of+tissues+of+cells.">Amount and distribution of 5-methylcytosine in human DNA from different types of tissues of cells.</a> Nucleic Acids Res. 10 (8), 2709-2721 (1982).</li><li>Lister, R., Pelizzola, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Human+DNA+methylomes+at+base+resolution+show+widespread+epigenomic+differences.">Human DNA methylomes at base resolution show widespread epigenomic differences.</a> Nature. 462 (7271), 315-322 (2009).</li><li>Yan, J., Zierath, J. 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M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=SLC25A26+overexpression+impairs+cell+function+via+mtDNA+hypermethylation+and+rewiring+of+methyl+metabolism.">SLC25A26 overexpression impairs cell function via mtDNA hypermethylation and rewiring of methyl metabolism.</a> FEBS J. 284 (6), 967-984 (2017).</li><li>Frommer, M., McDonald, L. E., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+genomic+sequencing+protocol+that+yields+a+positive+display+of+5-methylcytosine+residues+in+individual+DNA+strands.">A genomic sequencing protocol that yields a positive display of 5-methylcytosine residues in individual DNA strands.</a> PNAS. 89 (5), 1827-1831 (1992).</li><li>Byun, H. -. M., Panni, T., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effects+of+airborne+pollutants+on+mitochondrial+DNA+Methylation.">Effects of airborne pollutants on mitochondrial DNA Methylation.</a> Part Fibre Toxicol. 10 (1), 1 (2013).</li><li>Janssen, B. G., Byun, H. -. M., Gyselaers, W., Lefebvre, W., Baccarelli, A. A., Nawrot, T. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Placental+mitochondrial+methylation+and+exposure+to+airborne+particulate+matter+in+the+early+life+environment:+An+ENVIRONAGE+birth+cohort+study.">Placental mitochondrial methylation and exposure to airborne particulate matter in the early life environment: An ENVIRONAGE birth cohort study.</a> Epigenetics. 10 (6), 536-544 (2015).</li><li>Zheng, L. D., Linarelli, L. 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Here, we provide a bisulfite-sequencing protocol which is specifically designed to interrogate mtDNA methylation. The differences with bisulfite-sequencing protocols used for genomic DNA lies in the utilization of a prior restriction enzyme digestion step and a bioinformatic analysis ruling out false positive arising from NUMT sequences.
We provide a protocol to avoid bisulfite-sequencing artifacts when investigating mtDNA methylation. Bisulfite sequencing artifacts leading to false-positives ...

The mitochondrial genome is a circular, double-stranded structure of approximately 16.5-kilo base (kb) long, constituting of a heavy and a light strand. The mitochondrial genome is present in multiple copies within each cell, maternally-inherited, and encodes essential components of the respiratory chain complexes1. Similar to bacterial genomes and unlike the nuclear genome, the mitochondrial genome is organized in numerous secondary and tertiary structures, such as in coiled and supercoiled structures2, which can render access difficult during sequencing experiments3.
In the nucleus, methylation of the DNA is an extensively studied epigenetic mark that plays a role in numerous processes, notably in the regulation of gene expression. In mammalian genomes, DNA methylation occurs primarily on the 5-position of the pyrimidine ring of deoxycytidines, mostly on CG dinucleotides (or CpG). Cytosine methylation is found at 70% of all CpG in the genome of somatic cells and accounts for ~1% of total DNA bases4. DNA methylations has also been described in non-CpG contexts, such as CpA, CpT, and CpC and exist in various amounts in nuclear DNA, with values up to 25% of all methylated cytosines in embryonic stem cells5,6,7.
While cytosine methylation of the nuclear genome is widely accepted, the existence of mitochondrial DNA (mtDNA) methylation is still controversial. The first study investigating mtDNA methylation was performed in cultured cells where mtDNA methylation was readily detected, although at lower levels compared to nuclear DNA8. In both human and murine cells, mtDNA methylation was also detected at low levels (2-5%). Using assays relying on 5 methylcytosine capture such as methylated DNA immunoprecipitation (MeDIP) followed by quantitative PCR, mtDNA methylation was also detected in various mouse and human and cells lines9,10,11,12. Using antibodies against 5-methylcytosine in an ELISA assay or mass spectrometry, substantial levels of DNA methylation were detected from purified mitochondrial fractions13,14,15,16. However, most of the assays in the aforementioned studies used techniques that were not designed to provide absolute quantification of DNA methylation at the single base-resolution.
Quantitative and resolutive DNA methylation analysis can be achieved by a technique named &#34;bisulfite sequencing&#34;, which takes advantage of the property of sodium bisulfite to convert unmethylated cytosine into uracil in single-stranded DNA context17. Using bisulfite sequencing, a constellation of studies has detected the presence of cytosine methylation at various levels. Methylation mtDNA in the D-loop region, the 12S or the 16S region was readily detected in human18,19,20,21,22,23 and mouse24 tissues and cells, however, with an intriguing variability, of 1-20% of total cytosines across studies.
In comparison to these numerous studies, only a few studies, including from our group, have disputed the presence of mtDNA methylation3,25,26,27 or questioned the biological relevance of very low levels of mtDNA levels (below 2%)28. Recently, we reported the observation of a potential bisulfite-sequencing artifact in whole mitochondrial bisulfite sequencing3. We provided evidence that the secondary structure of mitochondrial DNA could lead to false positives in bisulfite sequencing, thereby overestimating methylation levels. We provide here a protocol to prevent an artifact of bisulfite-conversion of mtDNA. This protocol uses a simple enzymatic digestion of DNA to disrupt mtDNA secondary structures and allow full access to bisulfite following a bisulfite sequencing protocol. In addition, we provide an accompanying bioinformatic pipeline for the analysis of bisulfite sequencing.

<table border="0" cellpadding="0" cellspacing="0" width="648">
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:283px;">BamHI</td>
			<td style="width:164px;">New England BioLabs</td>
			<td style="width:113px;"># R0136</td>
			<td style="width:88px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">EZ DNA methylation-lightning kit</td>
			<td>Zymo Research</td>
			<td># D5030&#160;</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Qubit ssDNA assay</td>
			<td>Thermo Fisher Scientific</td>
			<td># Q10212</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Qubit assay tubes</td>
			<td>Thermo Fisher Scientific</td>
			<td># Q32856</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">HotStarTaq plus DNA polymerase kit</td>
			<td>Qiagen</td>
			<td># 203603&#160;</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">QIAquick Gel Extraction Kit</td>
			<td>Qiagen</td>
			<td># 28704</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">NEBNext Ultra DNA Library Kit for Illumina</td>
			<td>New England BioLabs</td>
			<td># E7370S</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">NEBNext Multiplex Oligoes for Illumina</td>
			<td>New England BioLabs</td>
			<td># E7335S</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">AMPure XP Beads</td>
			<td>Beckman Coulter</td>
			<td># A63881</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">High Sensitivity DNA chip</td>
			<td>Agilent</td>
			<td># 5067-4626</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Qubit high sensitivity dsDNA assay</td>
			<td>Thermo Fisher Scientific</td>
			<td># Q33230</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">MiSeq reagent kit v2 300 cycles</td>
			<td>Illumina</td>
			<td># MS-102-2003</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">PhiX control v3</td>
			<td>Illumina</td>
			<td># FC-110-3001</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Sodium hydroxide&#160;</td>
			<td>Sigma</td>
			<td># S5881</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Thermal cycler C1000</td>
			<td>Biorad</td>
			<td># 1851148</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">CFX96 Real-Time PCR detection system</td>
			<td>Biorad&#160;</td>
			<td>#1855195</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Qubit Fluorometer</td>
			<td>Thermo Fisher Scientific</td>
			<td># Q33226</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Bioanalyzer 2100</td>
			<td>Agilent</td>
			<td># G2939BA</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">MiSeq instrument</td>
			<td>Illumina</td>
			<td># SY-410-1003</td>
			<td></td>
		</tr>
	</tbody>
</table>

methodology for accurate detection of mitochondrial dna methylation

Quantification of DNA methylation can be achieved using bisulfite sequencing, which takes advantage of the property of sodium bisulfite to convert unmethylated cytosine into uracil, in a single-stranded DNA context. Bisulfite sequencing can be targeted (using PCR) or performed on the whole genome and provides absolute quantification of cytosine methylation at the single base-resolution. Given the distinct nature of nuclear- and mitochondrial DNA, notably in the secondary structure, adaptions of bisulfite sequencing methods for investigating cytosine methylation in mtDNA should be made. Secondary and tertiary structure of mtDNA can indeed lead to bisulfite sequencing artifacts leading to false-positives due to incomplete denaturation poor access of bisulfite to single-stranded DNA. Here, we describe a protocol using an enzymatic digestion of DNA with BamHI coupled with bioinformatic analysis pipeline to allow accurate quantification of cytosine methylation levels in mtDNA. In addition, we provide guidelines for designing the bisulfite sequencing primers specific to mtDNA, in order to avoid targeting undesirable NUclear MiTochondrial segments (NUMTs) inserted into the nuclear genome.

Two steps in this protocol are crucial when investigating mtDNA methylation. 1) The opening of the secondary structure and 2) the design of mitochondrial DNA-specific primers.
By digesting the human genomic DNA with the restriction enzyme BamHI (Figure 1), the mitochondrial DNA structure will be cut at nucleotide position 14,258 and the secondary structure will be opened.
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Watch this Scientific Journal Video about Methodology for Accurate Detection of Mitochondrial DNA Methylation at JoVE.com

Methodology for Accurate Detection of Mitochondrial DNA Methylation

Here, we present a protocol to allow accurate quantification of mitochondrial DNA (mtDNA) methylation. In this protocol, we describe an enzymatic digestion of DNA with BamHI coupled with a bioinformatic analysis pipeline which can be used to avoid overestimation of mtDNA methylation levels caused by the secondary structure of mtDNA.

Quantification of DNA methylation can be achieved using bisulfite sequencing, which takes advantage of the property of sodium bisulfite to convert ...

The overall goal of this bisulfite sequencing protocol and bioinformatic pipeline is to achieve an accurate quantification of mitochondrial DNA methylation. This method can help answer key questions in the mitoepigenetic field such as is mitochondrial DNA methylation changing human disease? The main advantage of this technique is that it allows for accurate quantification of mitochondrial DNA methylation.Crucial step when investigating mitochondrial DNA methylation is to linearize the mitochondrial DNA by BamH1 digestion before treatment with sodium bisulfite. The BamH1 restriction enzyme site is displayed in this map of the human mitochondrial genome. Also shown are the five regions of the mitochondrial genome that will be investigated by bisulfite sequencing.Displacement loop, tRNA phenylalanine, and 12S ribosome, 16S ribosome, NADH dehydrogenase 5, cytochrome B mRNA encoding gene. After designing the primers for bisulfite sequencing, using online tools as described in the text protocol, primer specificity toward the mitochondrial genome is verified using BiSearch. Primer sequences are added to the BiSearch function primer search.The bisulfite box is checked and a reference genome is selected. The search results will show potential PCR products generated on sense and antisense chains. To amplify the regions of interest from the bisulfite converted mitochondrial genome, perform PCR using a Hot-start Taq polymerase.If using primers separately, mix 100 nanograms of converted DNA, 500 micromolar of sense and antisense primers, one microliter dNTP mix and polymerase at 7.5 units per reaction in a total volume of 50 microliters. Run the PCR with the following conditions:five minutes at 95 degrees Celsius, one minute at 94 degrees Celsius, one minute at 55 degrees Celsius, one minute at 72 degrees Celsius for 35 cycles, followed by 10 minutes at 72 degrees Celsius. For multiplexing primers, use 200 nanograms of converted DNA in the following cycling conditions:five minutes at 95 degrees Celsius, one minute at 94 degrees Celsius, 1.5 minutes at 55 degrees Celsius, and 1.5 minutes at 72 degrees Celsius for 35 cycles, followed by 10 minutes at 72 degrees Celsius.When the PCR is complete, perform gel electrophoresis on the PCR products, using a 2%agarose at 100 volts. Extraction of the PCR products from the agarose gel must be done in a way that minimizes UV exposure and the risk of DNA damage. Take a photo of the gel under UV light.Then, very quickly, mark around the PCR product with a scalpel and turn off the UV light. Next, cut the PCR product slowly without exposure to UV light. Place the gel slices in microcentrifuge tubes and purify the PCR products using gel purification as described in the text protocol.Quantify the purified DNA using fluorometry. Store the samples at 20 degrees Celsius, if not proceeding immediately to bisulfite sequencing library preparation. Begin the library preparation of bisulfite converted PCR products by performing end repair using up to 100 nanograms of PCR product.To each 0.2 milliliter tube, add 55.5 microliters of PCR product, three microliters of end prep enzyme, and 6.5 microliters of 10X end repair reaction buffer. Incubate the tubes in a thermocycler at 20 degrees Celsius for 30 minutes, followed by 65 degrees Celsius for 30 minutes. Next, ligate sequencing adapters by mixing the end repaired DNA with 15 microliters of Blunt/TA ligase mix, 2.5 microliters of adapter, and one microliter of ligation enhancer.Place the mix in a thermocycler, and incubate at 20 degrees Celsius for 15 minutes. Pause the thermocycler and add 3 microliters of USER enzyme to each tube. Mix and place the tubes back in the thermocycler and incubate at 37 degrees Celsius for 15 minutes.Size select the adaptor-ligated DNA using solid phase reversible immobilization or SPRI. Add to the adaptor-ligated DNA 13.5 microliters of water and 55 microliters of resuspended SPRI beads. Incubate at room temperature for five minutes.Place the tubes on a magnetic stand. When the solution is clear, transfer the supernatant, containing the adaptor-ligated DNA, to a new tube, and discard the tube containing the beads. Add 25 microliters of resuspended SPRI beads to the supernatant;mix and incubate at room temperature for five minutes.Place the tubes on the magnetic stand and when the solution is clear, discard the supernatant. The adaptor-ligated DNA is now bound to the beads. While the tubes are on the magnetic stand, add 200 microliters of freshly prepared 80%ethanol to each tube and incubate for 30 seconds to wash the beads.Remove and discard the supernatant. Repeat this ethanol wash step for a total of two washes. Remove the ethanol from the second wash and air dry the beads by leaving the tubes on the magnetic stand, with the lid open, for five minutes.After five minutes, remove the tubes from the magnetic stand, add 23 microliter of DNA elution buffer to the beads and mix. Incubate at room temperature for two minutes. Place the tubes on the magnetic stand until the solution is clear.Then, transfer two microliter of the solution to a 96-Well PCR plate for the pre-PCR amplification. While carefully avoiding the beads, transfer the rest of the solution to a new 0.2 milliliter tube for PCR amplification. Perform pre-PCR amplification by RT-qPCR to estimate the number of cycles needed to amplify the adaptor-ligated DNA.Make a master mix of the following per reaction used. 0.4 microliters of index primer, 0.4 microliters of universal PCR primer, 7.2 microliters of water, and 10 microliters of RT-qPCR master mix. Then, mix the master mix and add 18 microliters of master mix to the two microliters of DNA in the 96-Well PCR plate.Place the plate in a real-time PCR machine and perform amplification under the following conditions:30 seconds at 98 degrees Celsius, 10 seconds at 98 degrees Celsius, and 75 seconds at 65 degrees Celsius for 20 cycles, followed by five minutes at 65 degrees Celsius. After estimating the number of amplification cycles needed for each sample, as described in the text protocol, amplify the adaptor-ligated DNA. For each sample, mix 21 microliters of DNA, 25 microliters of PCR master mix, one microliter of index primer, one microliter of universal PCR primer, and two microliters of water.In the thermocycler, subject each sample to the following conditions:30 seconds at 98 degrees Celsius, 10 seconds at 98 degrees Celsius, and 75 seconds at 65 degrees Celsius for the calculated number of cycles, followed by five minutes at 65 degrees Celsius. Purify the amplified DNA using SPRI beads, as demonstrated earlier and elute in 22 microliters of elution buffer. Control the library quality by using a Bioanalyzer.Look for correct library peak sizes. Estimate the average base pair size of the library products by smear analysis. In Advanced Global Settings, under Smear Analysis, double-click on Table.Find the region from 100 to 1000 base pair and click OK.Under Region Table, the defined region will appear and the library average size is calculated. Quantify the library by fluorometry. Store the library at 20 degrees Celsius until ready for next generation sequencing and computational analyses.By bisulfite sequencing, mitochondrial DNA methylation was investigated in undigested and digested total DNA from human skeletal muscle cells at five different regions of the mitochondrial genome. A full square represents cytosine guanine dinucleotide sites. The open square represents non-cytosine guanine dinucleotide sites.For undigested mitochondrial DNA, methylation levels ranged from 0-15.1%across all investigated regions. However, when the DNA was digested prior to bisulfite conversion, the uncoversion rate dropped to a maximum of 1%across all regions. This illustrates the importance of BamH1 digestion prior to bisulfite conversion to avoid overestimation of mitochondrial DNA methylation levels.After watching this video, you should have a good understanding on how to perform mitochondrial bisulfite sequencing, and by following our bioinformatic pipeline, you can achieve accurate quantification of mitochondrial DNA methylation.

methodology-for-accurate-detection-of-mitochondrial-dna-methylation

Research

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Genetics

Novel RNA-Binding Proteins Isolation by the RaPID Methodology

RNA-binding proteins (RBPs) play important roles in every aspect of RNA metabolism and regulation. Their identification is a major challenge in modern biology. Only a few in vitro and in vivo methods enable the identification of RBPs associated with a particular target mRNA. However, their main limitations are the identification of RBPs in a non-cellular environment (in vitro) or the low efficiency isolation of RNA of interest (in vivo). An RNA-binding protein purification and identification (RaPID) methodology was designed to overcome these limitations in yeast and enable efficient isolation of proteins that are associated in vivo. To achieve this, the RNA of interest is tagged with MS2 loops, and co-expressed with a fusion protein of an MS2-binding protein and a streptavidin-binding protein (SBP). Cells are then subjected to crosslinking and lysed, and complexes are isolated through streptavidin beads. The proteins that co-purify with the tagged RNA can then be determined by mass spectrometry. We recently used this protocol to identify novel proteins associated with the ER-associated PMP1 mRNA. Here, we provide a detailed protocol of RaPID, and discuss some of its limitations and advantages.

RNA-protein interactions lie at the heart of many cellular processes. Here, we describe an in vivo method to isolate specific RNA and identify novel proteins that are associated with it. This could shed new light on how RNAs are regulated in the cell.

RNA-binding proteins (RBPs) play important roles in every aspect of RNA metabolism and regulation. Their identification is a major challenge in modern ...

In Situ Labeling of Mitochondrial DNA Replication in Drosophila Adult Ovaries by EdU Staining

The mitochondrial genome is inherited exclusively through the maternal line. Understanding of how the mitochondrion and its genome are proliferated and transmitted from one generation to the next through the female oocyte is of fundamental importance. Because of the genetic tractability, and the elegant, ordered simplicity by which oocyte development proceeds, Drosophila oogenesis has become an invaluable system for mitochondrial study. An EdU (5-ethynyl-2&#180;-deoxyuridine) labeling method was utilized to detect mitochondrial DNA (mtDNA) replication in Drosophila ovaries. This method is superior to the BrdU (5-bromo-2'-deoxyuridine) labeling method in that it allows for good structural preservation and efficient fluorescent dye penetration of whole-mount tissues.
Here we describe a detailed protocol for labeling replicating mitochondrial DNA in Drosophila adult ovaries with EdU. Some technical solutions are offered to improve the viability of the ovaries, maintain their health during preparation, and ensure high-quality imaging. Visualization of newly synthesized mtDNA in the ovaries not only reveals the striking temporal and spatial pattern of mtDNA replication through oogenesis, but also allows for simple quantification of mtDNA replication under various genetic and pharmacological perturbations.

In Situ Labeling of Mitochondrial DNA Replication in Drosophila Adult Ovaries by EdU Staining

Drosophila oogenesis continues to be exceptionally useful in the study of mitochondrial proliferation and inheritance. This manuscript describes a detailed protocol used to label the replicating mitochondrial DNA (mtDNA) in Drosophila adult ovaries with 5-ethynyl-2&#180;-deoxyuridine (EdU), which facilitates uncovering mechanisms associated with mitochondrial inheritance that were previously debatable.

The mitochondrial genome is inherited exclusively through the maternal line. Understanding of how the mitochondrion and its genome are proliferated and ...

Comprehensive DNA Methylation Analysis Using a Methyl-CpG-binding Domain Capture-based Method in Chronic Lymphocytic Leukemia Patients

The role of long noncoding RNAs (lncRNAs) in cancer is coming to the forefront due to growing interest in understanding their mechanistic functions during cancer development and progression. Despite this, the global epigenetic regulation of lncRNAs and repetitive sequences in cancer has not been well investigated, particularly in chronic lymphocytic leukemia (CLL). This study focuses on a unique approach: the immunoprecipitation-based capture of double-stranded, methylated DNA fragments using methyl-binding domain (MBD) proteins, followed by next-generation sequencing (MBD-seq). CLL patient samples belonging to two prognostic subgroups (5 IGVH mutated samples + 5 IGVH unmutated samples) were used in this study. Analysis revealed 5,800 hypermethylated and 12,570 hypomethylated CLL-specific differentially methylated genes (cllDMGs) compared to normal healthy controls. Importantly, these results identified several CLL-specific, differentially methylated lncRNAs, repetitive elements, and protein-coding genes with potential prognostic value. This work outlines a detailed protocol for an MBD-seq and bioinformatics pipeline developed for the comprehensive analysis of global methylation profiles in highly CpG-rich regions using CLL patient samples. Finally, a protein-coding gene and an lncRNA were validated using pyrosequencing, which is a highly quantitative method to analyze CpG methylation levels to further corroborate the findings from the MBD-seq protocol.

This work describes an optimized methyl-CpG-binding domain (MBD) sequencing protocol and a computational pipeline to identify differentially methylated CpG-rich regions in chronic lymphocytic leukemia (CLL) patients.

The role of long noncoding RNAs (lncRNAs) in cancer is coming to the forefront due to growing interest in understanding their mechanistic functions during ...

Rare Event Detection Using Error-corrected DNA and RNA Sequencing

Conventional next-generation sequencing techniques (NGS) have allowed for immense genomic characterization for over a decade. Specifically, NGS has been used to analyze the spectrum of clonal mutations in malignancy. Though far more efficient than traditional Sanger methods, NGS struggles with identifying rare clonal and subclonal mutations due to its high error rate of ~0.5&#8211;2.0%. Thus, standard NGS has a limit of detection for mutations that are &#62;0.02 variant allele fraction (VAF). While the clinical significance for mutations this rare in patients without known disease remains unclear, patients treated for leukemia have significantly improved outcomes when residual disease is &#60;0.0001 by flow cytometry. In order to mitigate this artefactual background of NGS, numerous methods have been developed. Here we describe a method for Error-corrected DNA and RNA Sequencing (ECS), which involves tagging individual molecules with both a 16 bp random index for error-correction and an 8 bp patient-specific index for multiplexing. Our method can detect and track clonal mutations at variant allele fractions (VAFs) two orders of magnitude lower than the detection limit of NGS and as rare as 0.0001 VAF.

Next-generation sequencing (NGS) is a powerful tool for genomic characterization that is limited by the high error rate of the platform (~0.5&#8211;2.0%). We describe our methods of error-corrected sequencing that allow us to obviate the NGS error rate and detect mutations at variant allele fractions as rare as 0.0001.

Conventional next-generation sequencing techniques (NGS) have allowed for immense genomic characterization for over a decade. Specifically, NGS has been ...

Genome-wide Surveillance of Transcription Errors in Eukaryotic Organisms

Accurate transcription is required for the faithful expression of genetic information. Surprisingly though, little is known about the mechanisms that control the fidelity of transcription. To fill this gap in scientific knowledge, we recently optimized the circle-sequencing assay to detect transcription errors throughout the transcriptome of Saccharomyces cerevisiae, Drosophila melanogaster, and Caenorhabditis elegans. This protocol will provide researchers with a powerful new tool to map the landscape of transcription errors in eukaryotic cells so that the mechanisms that control the fidelity of transcription can be elucidated in unprecedented detail.

This protocol provides researchers with a new tool to monitor the fidelity of transcription in multiple model organisms.

Accurate transcription is required for the faithful expression of genetic information. Surprisingly though, little is known about the mechanisms that ...

ATAC-seq Assay with Low Mitochondrial DNA Contamination from Primary Human CD4+ T Lymphocytes

ATAC-seq has become a widely used methodology in the study of epigenetics due to its rapid and simple approach to mapping genome-wide accessible chromatin. In this paper we present an improved ATAC-seq protocol that reduces contaminating mitochondrial DNA reads. While previous ATAC-seq protocols have struggled with an average of 50% contaminating mitochondrial DNA reads, the optimized&#160;lysis buffer introduced in this protocol reduces mitochondrial DNA contamination to an average of 3%. This improved ATAC-seq protocol allows for a near 50% reduction in the sequencing cost. We demonstrate how these high-quality ATAC-seq libraries can be prepared from activated CD4+ lymphocytes, providing step-by-step instructions from CD4+ lymphocyte isolation from whole blood through data analysis. This improved ATAC-seq protocol has been validated in a wide range of cell types and will be of immediate use to researchers studying chromatin accessibility.

Here, we present a protocol to perform an assay for transposase-accessible chromatin sequencing (ATAC-seq) on activated CD4+ human lymphocytes. The protocol has been modified to minimize contaminating mitochondrial DNA reads from 50% to 3% through the introduction of a new lysis buffer.

ATAC-seq has become a widely used methodology in the study of epigenetics due to its rapid and simple approach to mapping genome-wide accessible ...

Single-Molecule F&ouml;rster Resonance Energy Transfer Methods for Real-Time Investigation of the Holliday Junction Resolution by GEN1

Bulk methods measure the ensemble behavior of molecules, in which individual reaction rates of the underlying steps are averaged throughout the population. Single-molecule F&#246;rster resonance energy transfer (smFRET) provides a recording of the conformational changes taking place by individual molecules in real-time. Therefore, smFRET is powerful in measuring structural changes in the enzyme or substrate during binding and catalysis. This work presents a protocol for single-molecule imaging of the interaction of a four-way Holliday junction (HJ) and gap endonuclease I (GEN1), a cytosolic homologous recombination enzyme. Also presented are single-color and two-color alternating excitation (ALEX) smFRET experimental protocols to follow the resolution of the HJ by GEN1 in real-time. The kinetics of GEN1 dimerization are determined at the HJ, which has been suggested to play a key role in the resolution of the HJ and has remained elusive until now. The techniques described here can be widely applied to obtain valuable mechanistic insights of many enzyme-DNA systems.

Single-Molecule F&amp;#246;rster Resonance Energy Transfer Methods for Real-Time Investigation of the Holliday Junction Resolution by GEN1

Presented here is a protocol for performing single-molecule F&#246;rster resonance energy transfer to study HJ resolution. Two-color alternating excitation is used for determining the dissociation constants. Single-color time lapse smFRET is then applied in real-time cleavage assays to obtain the dwell time distribution prior to HJ resolution.

Bulk methods measure the ensemble behavior of molecules, in which individual reaction rates of the underlying steps are averaged throughout the ...

Sample Preparation to Bioinformatics Analysis of DNA Methylation: Association Strategy for Obesity and Related Trait Studies

Obesity is directly connected to lifestyle and has been associated with DNA methylation changes that may cause alterations in the adipogenesis and lipid storage processes contributing to the development of the disease. We demonstrate a complete protocol from selection to epigenetic data analysis of patients with and without obesity. All steps from the protocol were tested and validated in a pilot study. 32 women participated in the study, in which 15 individuals were classified with obesity according to Body Mass Index (BMI) (45.1 &#177; 5.4 kg/m2); and 17 individuals were classified without obesity according to BMI (22.6 &#177; 1.8 kg/m2). In the group with obesity, 564 CpG sites related to fat mass were identified by linear regression analysis. The CpG sites were in the promoter regions. The differential analysis found 470 CpGs hypomethylated and 94 hypermethylated sites in individuals with obesity. The most hypomethylated enriched pathwayswere in the RUNX, WNT signaling, and response to hypoxia. The hypermethylated pathways were related to insulin secretion, glucagon signaling, and Ca2+. We conclude that the protocol effectively identified DNA methylation patterns and trait-related DNA methylation. These patterns could be associated with altered gene expression, affecting adipogenesis and lipid storage. Our results confirmed that an obesogenic lifestyle could promote epigenetic changes in human DNA.

The present study describes the workflow to manage DNA methylation data obtained by microarray technologies. The protocol demonstrates steps from sample preparation to data analysis. All procedures are described in detail, and the video shows the significant steps.

Obesity is directly connected to lifestyle and has been associated with DNA methylation changes that may cause alterations in the adipogenesis and lipid ...

Detection of Post-Replicative Gaps Accumulation and Repair in Human Cells Using the DNA Fiber Assay

The DNA fiber assay is a simple and robust method for the analysis of replication fork dynamics, based on the immunodetection of nucleotide analogs that are incorporated during DNA synthesis in human cells. However, this technique has a limited resolution of a few thousand kilobases. Consequently, post-replicative single-stranded DNA (ssDNA) gaps as small as a few hundred bases are not detectable by the standard assay. Here, we describe a modified version of the DNA fiber assay that utilizes the S1 nuclease, an enzyme that specifically cleaves ssDNA. In the presence of post-replicative ssDNA gaps, the S1 nuclease will target and cleave the gaps, generating shorter tracts that can be used as a read-out for ssDNA gaps on ongoing forks. These post-replicative ssDNA gaps are formed when damaged DNA is replicated discontinuously. They can be repaired via mechanisms uncoupled from genome replication, in a process known as gap-filling or post-replicative repair. Because gap-filling mechanisms involve DNA synthesis independent of the S phase, alterations in the DNA fiber labeling scheme can also be employed to monitor gap-filling events. Altogether, these modifications of the DNA fiber assay are powerful strategies to understand how post-replicative gaps are formed and filled in the genome of human cells.

Here we describe two modifications of the DNA fiber assay to investigate single-stranded DNA gaps in replicating DNA after lesion induction. The S1 fiber assay enables the detection of post-replicative gaps using the ssDNA-specific S1 endonuclease, while the gap-filling assay allows visualization and quantification of gap repair.

The DNA fiber assay is a simple and robust method for the analysis of replication fork dynamics, based on the immunodetection of nucleotide analogs that ...

Optimizing Low-Frequency Mutation Detection with Wild-Type Blocking PCR

Wild-type Blocking PCR Combined with Sanger Sequencing for Detection of Low-frequency Somatic Mutation

When monitoring minimal residual disease (MRD) after tumor treatment, there are higher requirements of the lower limit of detection than when detecting for drug resistance mutations and circulating tumor cell mutations during therapy. Traditional Sanger sequencing has 5%-20% wild-type mutation detection, so its limit of detection cannot meet the corresponding requirements. The wild-type blocking technologies that have been reported to overcome this include blocker displacement amplification (BDA), non-extendable locked nucleic acid (LNA), hot-spot-specific probes (HSSP), etc. These technologies use specific oligonucleotide sequences to block wild-type or recognize wild-type and then combine this with other methods to prevent wild-type amplification and amplify mutant amplification, leading to characteristics like high sensitivity, flexibility, and convenience. This protocol uses BDA, a wild-type blocking PCR combined with Sanger sequencing, to optimize the detection of RHOA G17V low-frequency somatic mutations, and the detection sensitivity can reach 0.5%, which can provide a basis for MRD monitoring of angioimmunoblastic T-cell lymphoma.

Author Spotlight: Advancing the Detection of Low-Frequency Mutations in Cancer Tissues

This article introduces the application of a low-frequency detection method based on Sanger sequencing in angioimmunoblastic lymphoma. Provide a basis for applying this method to other diseases.

When monitoring minimal residual disease (MRD) after tumor treatment, there are higher requirements of the lower limit of detection than when detecting ...