This research was funded by the National Institute for General Medical Science (NIGMS) (5605100122001), a component of the National Institutes of Health (NIH), as well as University of Nebraska at Kearney (UNK) Summer Student Research Program (SSRP), and UNK Undergraduate Research Fellowship (URF).

1. Preparation of Dyes, Buffers and Agarose Gel
<ol>
	<li>Prepare the following solutions for staining DNA or the digestion of stained DNA.
	<ol>
		<li>Prepare 1x TE (Tris-HCl and ethylenediaminetetraacetic acid; EDTA) buffer using 10 mM Tris-HCl and 1 mM EDTA in a graduated cylinder or volumetric flask. Store at room temperature (18 - 25 &#176;C).</li>
		<li>Make aliquots of each dye: TOTO-1, YOYO-1, POPO-1, BOBO-1, TOTO-3, YOYO-3, POPO-3, BOBO-3 (Table 1). Pipette 4 &#181;L of 1 mM dye into a dark amber or black 1.5 mL tube and add 36 &#181;L of 1x TE, mix using the pipette; this concentration makes a 100 &#181;M dye solution (40 &#181;L total). Complete this step for each dye. Store at 4 &#176;C. 
		NOTE: Avoid exposing dye to light to prevent photobleaching or degradation of the dye.</li>
		<li>Prepare buffer 1 using 10 mM Bis-Tris-Propane-HCl, 10 mM MgCl2, and 100 &#181;g/mL bovine serum albumin (BSA). Prepare buffer 2 using 50 mM NaCl, 10 mM Tris-HCl, 10 mM MgCl2, and 100 &#181;g/mL BSA. Prepare buffer 3 using 50 mM Potassium Acetate, 20 mM Tris-acetate, 10 mM magnesium acetate, and 100 &#181;g/mL BSA. Each enzyme will require one of these specific buffers to function.</li>
	</ol>
	</li>
	<li>Prepare the following solutions for gel electrophoresis.
	<ol>
		<li>Make a 6x loading dye by combining 0.25% bromophenol blue, 0.25% xylene cyanol, 15% Ficoll in dH2O. Store at room temperature.</li>
		<li>To make a 0.7% agarose gel, weigh out 0.07 g of high gelling temperature (HGT) agarose in an Erlenmeyer flask, add 100 mL of 1x TAE buffer and place an inverted beaker on top of the flask.
		<ol>
			<li>Heat the solution on a hot plate until bubbles begin to form on the bottom of the flask and float to the top.</li>
			<li>Remove the solution from the hot plate, let the solution cool until the flask can be touched with a bare hand, and then pour the gel into a 24.5 cm x 21.8 cm gel mold with a gel comb to create wells.</li>
			<li>Remove bubbles near the comb or on the surface of the gel by popping them with a pipette tip and allow the gel to solidify for at least 15 minutes. This can be stored in a fridge (4 &#176;C) wrapped in plastic wrap for 1 week to prevent drying of the gel or contamination. For more information on how to run a gel refer to Lee et al.33. 
			NOTE: Use a gel comb with 30 individual wells. Each well should be 4.5 mm wide with a depth of 2 mm. The height of the well will depend on the amount of gel poured into the box.</li>
		</ol>
		</li>
		<li>Prepare 1x TAE (Tris - acetate - EDTA) buffer using 40 mM Tris-HCl, 20 mM acetic acid, and 1 mM EDTA. Store at room temperature (18 - 25 &#176;C).</li>
	</ol>
	</li>
</ol>
2. Preparation of Stained DNA
<ol>
	<li>Stain lambda DNA (300-800 ng) using different aliquots of dyes. Each dye (Table 1) will have six different concentrations tested, for a total of 48 reactions per restriction enzyme. The following process outlines a set up for 1 reaction (Figure 1).
	<ol>
		<li>Dilute lambda DNA using 1x TE to 100 ng/&#181;L. Store in 4 &#176;C. Make a solution with total volume of 300 &#181;L.</li>
		<li>Stain unmethylated lambda DNA. For each band expected from the digest, estimate 75 - 100 ng/band. Add appropriate amounts of dye to produce concentrations of 1.9 &#181;M, 3.8 &#181;M, 19.4 &#181;M, 32.2 &#181;M, 48.3 &#181;M, 63.5 &#181;M / 100 ng of DNA.</li>
		<li>Incubate overnight (15 h - 18 h) at 4 &#176;C.</li>
		<li>Leave one reaction unstained to act as a control25. 
		NOTE: Use unmethylated DNA for the digestion reaction. Methylation sensitive enzymes cannot cut methylated regions in DNA and will give an appearance of an incomplete digestion.</li>
	</ol>
	</li>
</ol>
3. Preparation of the Restriction Enzyme Assay
<ol>
	<li>Digest stained DNA with a restriction enzyme to determine if that enzyme can digest prestained DNA (Figure 1).
	<ol>
		<li>The following day, add 20 U of restriction enzyme, 3 &#181;L of the appropriate buffer ( Table 2), and distilled, autoclaved and filtered water for a total of 30 &#181;L. For each enzyme reaction, choose the buffer with the highest cutting efficiency, which can be found on the manufacturer&#39;s website.</li>
		<li>Place the reactions in a water bath at the temperature of optimal enzymatic activity, listed in Table 2 for the 6 enzymes used in Maschmann et al., for 2 - 4 h (Table 2)25.</li>
		<li>Stop the reaction by adding 2 &#181;L of 0.5 M EDTA pH 8.0.</li>
	</ol>
	</li>
</ol>
4. Electroeluting Stained DNA in an Agarose Gel
<ol>
	<li>Remove the sides from the 24.5 cm x 21.8 cm gel mold (Step 1.2.2) and place the gel into the gel electrophoresis box. Pour 2.5 L of 1x TAE buffer into the box. Carefully remove the gel comb from the gel, so the wells are accessible33.</li>
	<li>Pipette the restriction enzyme reactions onto a plastic film and combine each reaction with 6x loading dye. For each reaction solution, add 1 &#181;L of 6x loading dye per 5 - 6 &#181;L of DNA solution (1x). Then pipette the reactions (containing the loading dye, &#60;18 &#181;L) into the wells.</li>
	<li>Mix 1 &#181;L of 1 kb ladder, 9 &#181;L of 1x TE, and 2 &#181;L of 6x loading dye. Load solution into the wells that flank the other solutions.</li>
	<li>Cover the gel box with dark blue or black paper or fabric. Connect the gel box to a power supply, set the power supply to 30 V, and run it overnight (15 - 20 h). Turn off the lights while the gel is running, to prevent photocleavage of the labeled DNA.</li>
	<li>The next morning turn off the power supply. Take the gel out using the tray and transfer it to a container with 45 &#181;L ethidium bromide and 1 L of 1x TAE buffer. Store the container at room temperature in the dark or cover in foil to prevent exposure to light. Let gel stain for at least 45 min at room temperature. 
	CAUTION: Use ethidium bromide with gloves and wear safety glasses. When cleaning out the container containing ethidium bromide solution and throwing away the gel, consult your states disposal guidelines to determine how to deal with used ethidium bromide; additionally, other stains may be utilized instead of ethidium bromide.</li>
</ol>
5. Imaging the Agarose Gel
<ol>
	<li>Place the gel on top of a blue light transilluminator, which emits maximum light output between 400-500 nm. Take pictures with the camera attached to the station. 
	CAUTION: Make sure to use the cover for the illuminator and put on protective glasses prior to turning on the light source. 
	NOTE: This step may also be completed using any UV light source or standard gel scanner.</li>
	<li>View the pictures in ImageJ by dragging the file to the ImageJ status bar and the image will pop up.</li>
	<li>Determine the digestion rate for the experiment by comparing the bands on the gel to the expected in silico gel pattern. To determine the digestion rate, the number of experimental bands is divided by the expected number of DNA bands24,25. If the experimental digested DNA band pattern has the expected pattern, the digestion rate is 1. If the pattern has more fragments than expected, the digestion rate is greater than 1. If the pattern has less fragments than expected, the digestion rate is less than one.</li>
</ol>

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The authors have nothing to disclose.

In order to digest fluorescently labeled DNA (Figure 1), a series of steps are required. First, DNA is stained with a fluorochrome overnight. DNA can be incubated with cyanine dimers for a shorter period of time; however, Carlsson et al. found that DNA created double bands for each DNA size due to incomplete staining20. To remedy this, the DNA can be stained overnight to prevent double bands from occurring. This is a critical step in the prot...

The TOTO series (TOTO-1, YOYO-1, POPO-1, BOBO-1, TOTO-3, YOYO-3, POPO-3, and BOBO-3; Table 1) is utilized in a wide variety of experiments where the visualization of DNA is required1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17. The cyanine dimer family is widely used due to their quantum yield, sensitivity, and high affinity for DNA molecules18,19,20. Cyanine dimer dyes have great selectivity for double stranded DNA and when intercalated have a 100 to 1000 fold increase of fluorescence21. Pyridinium dyes (YOYO-1, TOTO-1, YOYO-3, and TOTO-3) have a shorter emission wavelength than their quinolium dye (BOBO-1, POPO-1, BOBO-3, and POPO-3) counterparts (Table 1)22. Also, the quantum yield for cyanine dimers intercalated into DNA is high (0.2 - 0.6)22. However, using an enzyme to determine the methylation profile of a DNA molecule2 or stretch23 of a DNA molecule already stained with fluorescent dye requires a method to determine what enzymes will digest stained DNA. Any type of dye that intercalates into DNA or any enzyme that gives a discernable pattern of the DNA substrate can be used for this method.
Meng et al. first determined the digestion rate of prestained DNA through gel electrophoresis using a variety of different dyes24. Maschmann et al. delved in deeper to look at the TOTO family of dyes. Both determined the digestion rate of stained DNA to see if DNA stained with a given dye could be digested with a restriction enzyme25. Other methods study binding effects of dyes intercalated with DNA using optical tweezers26 or NMR27. Either method requires specialized equipment; whereas, this method allows equipment that most molecular biology labs have to determine if a dye interferes with a restriction enzyme digestion.
Additionally, in other methods to measure the length of a given molecule, optical mapping has elongated unstained DNA molecules on a surface and digested DNA to determine the stretch and size of fragments. Intercalation of dye has been shown to increase the contour length of fluorescently stained DNA molecules and depending on the dye used, the contour lengths are different21. This method has been utilized in a variety of genomes1,3,4,6,13,28,29,30,31. However, if molecules were pre-stained, depending on the dye and enzyme, the enzyme may not be able to cut DNA stained with a given dye. Therefore, this method determines if DNA stained with a given dye can be digested with an enzyme. Additionally, depending on the concentration of the dye and the dye utilized, the mobility of the DNA bands in a gel will migrate more slowly than native DNA due to the partial unwinding of the DNA backbone to make room for the dye to insert between base pairs32.
However, sometimes these dyes can partially or completely inhibit the action of certain restriction enzymes7,24. This is thought to be due to a structural change in DNA caused by the attachment of the fluorescent dye, which may prevent the enzyme from recognizing its specific sequence. Understanding how these dyes affect restriction enzymes can help in experiments where the methylation profile or the stretch of stained DNA is required.
In our method, DNA was stained with a fluorochrome of interest and digested with a restriction enzyme. Then DNA was electrophoresed on a gel, imaged, and the restriction enzyme digestion rate was measured. The restriction enzymes were chosen based on the cut pattern on a gel. Too many bands caused overlap of DNA bands and too few bands did not give a complete picture of the DNA molecule. There is a sweet spot to be able to determine the profile of the digested DNA molecule; therefore, it will depend on the DNA used and the enzyme. An advantage of this method is its simplicity; it only requires equipment used in a restriction digestion and gel electrophoresis.

<table><tbody><tr><td>Unmethylated lambda DNA</td><td>NEB</td><td>N3013S</td><td></td></tr><tr><td>YOYO-1</td><td>ThermoFisher Scientific</td><td>Y3601</td><td></td></tr><tr><td>TOTO-1</td><td>ThermoFisher Scientific</td><td>T3600</td><td></td></tr><tr><td>POPO-1</td><td>ThermoFisher Scientific</td><td>P3580</td><td></td></tr><tr><td>BOBO-1</td><td>ThermoFisher Scientific</td><td>B3582</td><td></td></tr><tr><td>YOYO-3</td><td>ThermoFisher Scientific</td><td>Y3606</td><td></td></tr><tr><td>TOTO-3</td><td>ThermoFisher Scientific</td><td>T3604</td><td></td></tr><tr><td>POPO-3</td><td>ThermoFisher Scientific</td><td>P3584</td><td></td></tr><tr><td>BamHI</td><td>NEB</td><td>R0136S</td><td></td></tr><tr><td>PmlI</td><td>NEB</td><td>R0532S</td><td></td></tr><tr><td>ScaI</td><td>NEB</td><td>R3122S</td><td></td></tr><tr><td>EcoRI&amp;nbsp;</td><td>NEB</td><td>R0101S</td><td></td></tr><tr><td>HindIII</td><td>NEB</td><td>R0104S</td><td></td></tr><tr><td>SmaI</td><td>NEB</td><td>R0141S</td><td></td></tr><tr><td>Tris</td><td>Fisher</td><td>BP152-1</td><td>Irritant</td></tr><tr><td>EDTA</td><td>Fisher</td><td>S316-212</td><td>Toxic</td></tr><tr><td>HCl</td><td>Fisher</td><td>S25358</td><td>Corrosive and irritant</td></tr><tr><td>Buffer 1</td><td>NEB</td><td>B7201S</td><td>NEB 1.1</td></tr><tr><td>Buffer 2</td><td>NEB</td><td>B7202S</td><td>NEB 2.1</td></tr><tr><td>Buffer 3</td><td>NEB</td><td>B7204S</td><td>NEB Cutsmart</td></tr><tr><td>High gelling temperature agarose gel</td><td>Lonza</td><td>50041</td><td></td></tr><tr><td>Acetic Acid</td><td>Fisher</td><td>S25118</td><td>Hazardous</td></tr><tr><td>Blue light transilluminator</td><td>Dark Reader</td><td>DR196</td><td>Wear correct eyewear&amp;nbsp;</td></tr><tr><td>Ethidium bromide</td><td>Fisher</td><td>15585011</td><td>Carcinogen; other alternatives are Nancy 520, Gel red, etc.</td></tr><tr><td>Cannon EOS Rebel T3I camera</td><td>Cannon</td><td></td><td></td></tr><tr><td>Apogee Model H4</td><td>Biorad</td><td>1704510</td><td></td></tr><tr><td>Power Pac Basic Power Supply</td><td>Biorad</td><td>1645050&amp;nbsp;</td><td></td></tr><tr><td>Ficoll</td><td>Fisher Scientific</td><td>BP525-25</td><td></td></tr><tr><td>Bromophenol blue</td><td>Fisher Scientific</td><td>B-392</td><td></td></tr><tr><td>Xylene Cyanol</td><td>Eastmen</td><td>T1579</td><td></td></tr></tbody></table>

determining if dna stained with a cyanine dye can be digested with restriction enzymes

Visualization of DNA for fluorescence microscopy utilizes a variety of dyes such as cyanine dyes. These dyes are utilized due to their high affinity and sensitivity for DNA. In order to determine if the DNA molecules are full length after the completion of the experiment, a method is required to determine if the stained molecules are full length by digesting DNA with restriction enzymes. However, stained DNA may inhibit the enzymes, so a method is needed to determine what enzymes one could use for fluorochrome stained DNA. In this method, DNA is stained with a cyanine dye overnight to allow the dye and DNA to equilibrate. Next, stained DNA is digested with a restriction enzyme, loaded into a gel and electrophoresed. The experimental DNA digest bands are compared to an in silico digest to determine the restriction enzyme activity. If there is the same number of bands as expected, then the reaction is complete. More bands than expected indicate partial digestion and less bands indicate incomplete digestion. The advantage of this method is its simplicity and it uses equipment that a scientist would need for a restriction enzyme assay and gel electrophoresis. A limitation of this method is that the enzymes available to most scientists are commercially available enzymes; however, any restriction enzymes could be used.

In order to determine if an intercalating dye will affect a restriction enzyme digesting DNA, the correct order of steps must be followed (Figure 1). Once DNA is stained and digested with a given enzyme, a picture of the gel can be taken to determine the number of fragments and their size (Figure 2). In order to determine the enzyme efficiency, the total number of expected visible bands divided by the number of visible bands. Enz...

Watch this Scientific Journal Video about Determining if DNA Stained with a Cyanine Dye Can Be Digested with Restriction Enzymes at JoVE.com

Determining if DNA Stained with a Cyanine Dye Can Be Digested with Restriction Enzymes

Staining DNA molecules for fluorescence microscopy allows a scientist to view them during an experiment. In the method presented here, DNA molecules are pre-stained with fluorescent dyes and digested with methylation and non-methylation sensitive restriction enzymes.

Visualization of DNA for fluorescence microscopy utilizes a variety of dyes such as cyanine dyes. These dyes are utilized due to their high affinity and ...

determining-if-dna-stained-with-cyanine-dye-can-be-digested-with

Research

JoVE Journal

Biochemistry

8.7K Views.  University of Nebraska - Kearney. Staining DNA molecules for fluorescence microscopy allows a scientist to view them during an experiment. In the method presented here, DNA molecules are pre-stained with fluorescent dyes and digested with methylation and non-methylation sensitive restriction enzymes.

Video: Determining if DNA Stained with a Cyanine Dye Can Be Digested with Restriction Enzymes

DNA Staining Method Based on Formazan Precipitation Induced by Blue Light Exposure

DNA staining methods are very important for biomedical research. We designed a simple method that allows DNA visualization to the naked eye by the formation of a colored precipitate. It works by soaking the acrylamide or agarose DNA gel in a solution of 1x (equivalent to 2.0 &#181;M) SYBR Green I (SG I) and 0.20 mM nitro blue tetrazolium that produces a purple precipitate of formazan when exposed to sunlight or specifically blue light. Also, DNA recovery tests were performed using an ampicillin resistant plasmid in an agarose gel stained with our method. A larger number of colonies was obtained with our method than with traditional staining using SG I with ultraviolet illumination. The described method is fast, specific, and non-toxic for DNA detection, allowing visualization of biomolecules to the "naked eye" without a transilluminator, and is inexpensive and appropriate for field use. For these reasons, our new DNA staining method has potential benefits to both research and industry.

This method allows selective staining and quantification of DNA in gels by soaking the gel in a SYBR Green I/Nitro Blue Tetrazolium solution and then exposing it to sunlight or a blue light source. This produces a visible precipitate and requires almost no equipment, making it ideal for field use.

DNA staining methods are very important for biomedical research. We designed a simple method that allows DNA visualization to the naked eye by the ...

Detection of Bacteria Using Fluorogenic DNAzymes

Outbreaks linked to food-borne and hospital-acquired pathogens account for millions of deaths and hospitalizations as well as colossal economic losses each and every year. Prevention of such outbreaks and minimization of the impact of an ongoing epidemic place an ever-increasing demand for analytical methods that can accurately identify culprit pathogens at the earliest stage. Although there is a large array of effective methods for pathogen detection, none of them can satisfy all the following five premier requirements embodied for an ideal detection method: high specificity (detecting only the bacterium of interest), high sensitivity (capable of detecting as low as a single live bacterial cell), short time-to-results (minutes to hours), great operational simplicity (no need for lengthy sampling procedures and the use of specialized equipment), and cost effectiveness. For example, classical microbiological methods are highly specific but require a long time (days to weeks) to acquire a definitive result.1 PCR- and antibody-based techniques offer shorter waiting times (hours to days), but they require the use of expensive reagents and/or sophisticated equipment.2-4 Consequently, there is still a great demand for scientific research towards developing innovative bacterial detection methods that offer improved characteristics in one or more of the aforementioned requirements. Our laboratory is interested in examining the potential of DNAzymes as a novel class of molecular probes for biosensing applications including bacterial detection.5
DNAzymes (also known as deoxyribozymes or DNA enzymes) are man-made single-stranded DNA molecules with the capability of catalyzing chemical reactions.6-8 These molecules can be isolated from a vast random-sequence DNA pool (which contains as many as 1016 individual sequences) by a process known as "in vitro selection" or "SELEX" (systematic evolution of ligands by exponential enrichment).9-16 These special DNA molecules have been widely examined in recent years as molecular tools for biosensing applications.6-8
Our laboratory has established in vitro selection procedures for isolating RNA-cleaving fluorescent DNAzymes (RFDs; Fig. 1) and investigated the use of RFDs as analytical tools.17-29 RFDs catalyze the cleavage of a DNA-RNA chimeric substrate at a single ribonucleotide junction (R) that is flanked by a fluorophore (F) and a quencher (Q). The close proximity of F and Q renders the uncleaved substrate minimal fluorescence. However, the cleavage event leads to the separation of F and Q, which is accompanied by significant increase of fluorescence intensity.
More recently, we developed a method of isolating RFDs for bacterial detection.5 These special RFDs were isolated to "light up" in the presence of the crude extracellular mixture (CEM) left behind by a specific type of bacteria in their environment or in the media they are cultured (Fig. 1). The use of crude mixture circumvents the tedious process of purifying and identifying a suitable target from the microbe of interest for biosensor development (which could take months or years to complete). The use of extracellular targets means the assaying procedure is simple because there is no need for steps to obtain intracellular targets.
Using the above approach, we derived an RFD that cleaves its substrate (FS1; Fig. 2A) only in the presence of the CEM produced by E. coli (CEM-EC).5 This E. coli-sensing RFD, named RFD-EC1 (Fig. 2A), was found to be strictly responsive to CEM-EC but nonresponsive to CEMs from a host of other bacteria (Fig. 3).
Here we present the key experimental procedures for setting up E. coli detection assays using RFD-EC1 and representative results.

We have recently reported a novel approach for generating fluorogenic DNAzyme probes that can be applied to set up a simple, "mix-and-read" fluorescent assay for bacterial detection. These special DNA probes catalyze the cleavage of a chromophore-modified DNA-RNA chimeric substrate in the presence of crude extracellular mixture (CEM) produced by a specific bacterium, thereby translating bacterial detection into fluorescence signal generation. In this report we will describe key experimental procedures where a specific DNAzyme probe denoted "RFD-EC1" is employed for the detection of the model bacterium, Escherichia coli (E. coli).

Outbreaks linked to food-borne and hospital-acquired pathogens account for millions of deaths and hospitalizations as well as colossal economic losses ...

Immunology and Infection

DNA Electrophoresis Using Thiazole Orange Instead of Ethidium Bromide or Alternative Dyes

DNA gel electrophoresis using agarose is a common tool in molecular biology laboratories, allowing separation of DNA fragments by size. After separation, DNA is visualized by staining. This article demonstrates how to use thiazole orange to stain DNA. Thiazole orange compares favorably to common staining methods, in that it is sensitive, inexpensive, excitable with UV or blue light (to prevent sample damage), and safer than ethidium bromide. Labs already equipped to run DNA electrophoresis experiments using ethidium bromide can generally switch dyes with no additional changes to existing protocols, using UV light for detection. Blue-light detection to avoid sample damage can additionally be achieved with a blue-light source and emission filter. Labs already equipped for blue-light detection can simply switch dyes with no additional changes to existing protocols.

Here, we present a protocol to use thiazole orange for the detection of DNA in gel electrophoresis experiments. The use of thiazole orange allows elimination of ethidium bromide, and fluorescence detection can be achieved with either UV or blue light.

DNA gel electrophoresis using agarose is a common tool in molecular biology laboratories, allowing separation of DNA fragments by size. After separation, ...

In-Nucleus Hi-C in Drosophila Cells

The genome is organized into topologically associating domains (TADs) delimited by boundaries that isolate interactions between domains. In Drosophila, the mechanisms underlying TAD formation and boundaries are still under investigation. The application of the in-nucleus Hi-C method described here helped to dissect the function of architectural protein (AP)-binding sites at TAD boundaries isolating the Notch gene. Genetic modification of domain boundaries that cause loss of APs results in TAD fusion, transcriptional defects, and long-range topological alterations. These results provided evidence demonstrating the contribution of genetic elements to domain boundary formation and gene expression control in Drosophila. Here, the in-nucleus Hi-C method has been described in detail, which provides important checkpoints to assess the quality of the experiment along with the protocol. Also shown are the required numbers of sequencing reads and valid Hi-C pairs to analyze genomic interactions at different genomic scales. CRISPR/Cas9-mediated genetic editing of regulatory elements and high-resolution profiling of genomic interactions using this in-nucleus Hi-C protocol could be a powerful combination for the investigation of the structural function of genetic elements.

The genome is organized in the nuclear space into different structures that can be revealed through chromosome conformation capture technologies. The in-nucleus Hi-C method provides a genome-wide collection of chromatin interactions in Drosophila cell lines, which generates contact maps that can be explored at megabase resolution at restriction fragment level.

The genome is organized into topologically associating domains (TADs) delimited by boundaries that isolate interactions between domains. In Drosophila, ...

Genetics

Chromosome Conformation Capture (3C) for Undergraduate Research and Teaching

Getting an A with the 3Cs: Chromosome Conformation Capture for Undergraduates

Chromosome conformation capture (3C) is a powerful tool that has spawned a family of similar techniques (e.g., Hi-C, 4C, and 5C, referred to here as 3C techniques) that provide detailed information of the three-dimensional organization of chromatin. The 3C techniques have been used in a wide range of studies, from monitoring the changes in chromatin organization in cancer cells to identifying enhancer contacts made with gene promoters. While many of the studies using these techniques are asking big genome-wide questions with intricate sample types (i.e., single-cell analysis), what is often lost is that the 3C techniques are grounded in basic molecular biology methods that are applicable to a broad range of studies. By addressing tightly focused questions of chromatin organization, this cutting-edge technique can be used to enhance the undergraduate research and teaching lab experience. This paper presents a 3C protocol and provides adaptations and points of emphasis for implementation at primarily undergraduate institutions in undergraduate research and teaching experiences.

Author Spotlight: Getting an A with the 3Cs: Chromosome Conformation Capture for Undergraduates  

Here, we present an adaption of the chromosome conformation capture (3C) technique in detail with an emphasis on undergraduate involvement and learning.

Chromosome conformation capture (3C) is a powerful tool that has spawned a family of similar techniques (e.g., Hi-C, 4C, and 5C, referred to here as 3C ...

Single-Molecule Dwell-Time Analysis of Restriction Endonuclease-Mediated DNA Cleavage

This novel total internal reflection fluorescence microscopy-based assay facilitates the simultaneous measurement of the length of the catalytic cycle for hundreds of individual restriction endonuclease (REase) molecules in one experiment. This assay does not require protein labeling and can be carried out with a single imaging channel. In addition, the results of multiple individual experiments can be pooled to generate well-populated dwell-time distributions. Analysis of the resulting dwell-time distributions can help elucidate the DNA cleavage mechanism by revealing the presence of kinetic steps that cannot be directly observed. Example data collected using this assay with the well-studied REase, EcoRV - a dimeric Type IIP restriction endonuclease that cleaves the palindromic sequence GAT&#8595;ATC (where &#8595; is the cut site) - are in agreement with prior studies. These results suggest that there are at least three steps in the pathway to DNA cleavage that is initiated by introducing magnesium after EcoRV binds DNA in its absence, with an average rate of 0.17 s-1 for each step.

Using quantum-dot-labeled DNA and total internal reflection fluorescence microscopy, we can investigate the reaction mechanism of restriction endonucleases while using unlabeled protein. This single-molecule technique allows for massively multiplexed observation of individual protein-DNA interactions, and data can be pooled to generate well-populated dwell-time distributions.

This novel total internal reflection fluorescence microscopy-based assay facilitates the simultaneous measurement of the length of the catalytic cycle for ...

DNA-based Fish Species Identification Protocol

We have developed a fast, simple, and accurate DNA-based screening method to identify the fish species present in fresh and processed seafood samples. This versatile method employs PCR amplification of genomic DNA extracted from fish samples, followed by restriction fragment length polymorphism (RFLP) analysis to generate fragment patterns that can be resolved on the Agilent 2100 Bioanalyzer and matched to the correct species using RFLP pattern matching software.
The fish identification method uses a simple, reliable, spin column- based protocol to isolate DNA from fish samples. The samples are treated with proteinase K to release the nucleic acids into solution. DNA is then isolated by suspending the sample in binding buffer and loading onto a micro- spin cup containing a silica- based fiber matrix. The nucleic acids in the sample bind to the fiber matrix. The immobilized nucleic acids are washed to remove contaminants, and total DNA is recovered in a final volume of 100 &mu;l. The isolated DNA is ready for PCR amplification with the provided primers that bind to sequences found in all fish genomes. The PCR products are then digested with three different restriction enzymes and resolved on the Agilent 2100 Bioanalyzer. The fragment lengths produced in the digestion reactions can be used to determine the species of fish from which the DNA sample was prepared, using the RFLP pattern matching software containing a database of experimentally- derived RFLP patterns from commercially relevant fish species.

This publication describes how to use the Agilent Fish Species Identification System to identify the species of a fish by extracting DNA and performing PCR and RFLP analysis.

We have developed a fast, simple, and accurate DNA-based screening method to identify the fish species present in fresh and processed seafood samples. ...

Biology

Studying TRF1/2 Interactions with Telomeric DNA Using Single-Molecule Assay

Analyzing Telomeric Protein-DNA Interactions Using Single-Molecule Magnetic Tweezers

Telomeres, the protective structures at the ends of chromosomes, are crucial for maintaining cellular longevity and genome stability. Their proper function depends on tightly regulated processes of replication, elongation, and damage response. The shelterin complex, especially Telomere Repeat-binding Factor 1 (TRF1) and TRF2, plays a pivotal role in telomere protection and has emerged as a potential anti-cancer target for drug discovery. These proteins bind to the repetitive telomeric DNA motif TTAGGG, facilitating the formation of protective structures and recruitment of other telomeric proteins. Structural methods and advanced imaging techniques have provided insights into telomeric protein-DNA interactions, but probing the dynamic processes requires single-molecule approaches. Tools like magnetic tweezers, optical tweezers, and atomic force microscopy (AFM) have been employed to study telomeric protein-DNA interactions, revealing important details such as TRF2-dependent DNA distortion and telomerase catalysis. However, the preparation of single-molecule constructs with telomeric repetitive motifs continues to be a challenging task, potentially limiting the breadth of studies utilizing single-molecule mechanical methods. To address this, we developed a method to study interactions using full-length human telomeric DNA with magnetic tweezers. This protocol describes how to express and purify TRF2, prepare telomeric DNA, set up single-molecule mechanical assays, and analyze data. This detailed guide will benefit researchers in telomere biology and telomere-targeted drug discovery.

Author Spotlight: Advanced Single-Molecule Techniques for Investigating Telomeric Protein-DNA Interactions

This protocol demonstrates using single-molecule magnetic tweezers to study interactions between telomeric DNA-binding proteins (Telomere Repeat-binding Factor 1 [TRF1] and TRF2) and long telomeres extracted from human cells. It describes the preparatory steps for telomeres and telomeric repeat-binding factors, the execution of single-molecule experiments, and the data collection and analysis methods.

Telomeres, the protective structures at the ends of chromosomes, are crucial for maintaining cellular longevity and genome stability. Their proper ...

Selective Capture of 5-hydroxymethylcytosine from Genomic DNA

5-methylcytosine (5-mC) constitutes ~2-8% of the total cytosines in human genomic DNA and impacts a broad range of biological functions, including gene expression, maintenance of genome integrity, parental imprinting, X-chromosome inactivation, regulation of development, aging, and cancer1. Recently, the presence of an oxidized 5-mC, 5-hydroxymethylcytosine (5-hmC), was discovered in mammalian cells, in particular in embryonic stem (ES) cells and neuronal cells2-4. 5-hmC is generated by oxidation of 5-mC catalyzed by TET family iron (II)/&alpha;-ketoglutarate-dependent dioxygenases2, 3. 5-hmC is proposed to be involved in the maintenance of embryonic stem (mES) cell, normal hematopoiesis and malignancies, and zygote development2, 5-10. To better understand the function of 5-hmC, a reliable and straightforward sequencing system is essential. Traditional bisulfite sequencing cannot distinguish 5-hmC from 5-mC11. To unravel the biology of 5-hmC, we have developed a highly efficient and selective chemical approach to label and capture 5-hmC, taking advantage of a bacteriophage enzyme that adds a glucose moiety to 5-hmC specifically12.
Here we describe a straightforward two-step procedure for selective chemical labeling of 5-hmC. In the first labeling step, 5-hmC in genomic DNA is labeled with a 6-azide-glucose catalyzed by &beta;-GT, a glucosyltransferase from T4 bacteriophage, in a way that transfers the 6-azide-glucose to 5-hmC from the modified cofactor, UDP-6-N3-Glc (6-N3UDPG). In the second step, biotinylation, a disulfide biotin linker is attached to the azide group by click chemistry. Both steps are highly specific and efficient, leading to complete labeling regardless of the abundance of 5-hmC in genomic regions and giving extremely low background. Following biotinylation of 5-hmC, the 5-hmC-containing DNA fragments are then selectively captured using streptavidin beads in a density-independent manner. The resulting 5-hmC-enriched DNA fragments could be used for downstream analyses, including next-generation sequencing.
Our selective labeling and capture protocol confers high sensitivity, applicable to any source of genomic DNA with variable/diverse 5-hmC abundances. Although the main purpose of this protocol is its downstream application (i.e., next-generation sequencing to map out the 5-hmC distribution in genome), it is compatible with single-molecule, real-time SMRT (DNA) sequencing, which is capable of delivering single-base resolution sequencing of 5-hmC.

Described is a two-step labeling process using &beta;-glucosyltransferase (&beta;-GT) to transfer an azide-glucose to 5-hmC, followed by click chemistry to transfer a biotin linker for easy and density-independent enrichment. This efficient and specific labeling method enables enrichment of 5-hmC with extremely low background and high-throughput epigenomic mapping via next-generation sequencing.

5-methylcytosine (5-mC) constitutes ~2-8% of the total cytosines in human genomic DNA and impacts a broad range of biological functions, including gene ...

DNA Isolation and Restriction Enzyme Analysis

The revelation of DNA as the hereditary molecule in all organisms has led to enormous scientific and medical breakthroughs and significantly enhanced our understanding of ourselves and other organisms. DNA isolation and profiling have been the fundamental first steps for many of the advancements in the past century; from identification of gene function, to revolutions of agriculture and forensics.

<h4>Isolating DNA from Cells</h4>

DNA isolation is a fairly simple procedure that requires few but essential steps: cell harvesting, lysis, protein degradation, and finally DNA precipitation. Generally, DNA can be harvested from small amounts of tissue, such as a single leaf of a plant, hair follicles of animals, or epithelial cells that can be easily sloughed off within the mouth with a simple saline solution. Since DNA is compartmentalized inside the nucleus or mitochondria within eukaryotic cells, scientists first break apart the cell and nuclear membrane to expose the DNA, which is done with the lysis step. However, once DNA is exposed, it can be degraded by heavy metal ions and extremes of pH. Therefore, a detergent-containing buffer solution is used to not only dissolve the cell membrane, but also to protect DNA from degrading elements in the solution. Moreover, DNA is an unusually long molecule that is condensed inside the nucleus by packing tightly around special proteins called histones. Therefore, an enzyme called Proteinase K, which degrades peptide bonds of proteins, is added to separate the DNA from histones and other proteins. Next, scientists separate DNA from the rest of the cellular extract by using its chemical properties. Due to the negatively charged structure of nucleic acids, Na+ ions in a sodium chloride solution bind to and integrate into entangled DNA strands. Once the DNA is clumped, it can be observed by the naked eye. DNA is insoluble in alcohol and readily precipitates at low temperatures, thus scientists add cold alcohol to precipitate DNA. Finally, the precipitated DNA can be dissolved and stored in deionized water or a mild buffer, free of any enzymes that can degrade nucleic acids, until it is used.

<h4>Quantifying DNA</h4>

Reactions that use DNA often require high purity and precise amounts of DNA. Therefore, following DNA isolation, scientists use a spectrophotometer to quantify the amount of DNA in their sample, as well as the purity of the DNA in the sample. A spectrophotometer measures the intensity of a light beam passed through a sample as a function of its wavelength. Nucleic acids absorb light at 260 nm, whereas proteins absorb light at 280 nm. By measuring the intensity of a light beam at 260 nm, scientists can determine the DNA concentration. Furthermore, by assessing the light intensity at both 260 nm and 280 nm, the purity of the DNA content can be determined. In a sample of pure DNA, the 260/280 nm ratio should approach the value of 2.

<h4>Restriction Enzymes</h4>

For a number of analyses, such as cloning, sequencing, and mapping DNA fragments and genomes, the isolated DNA needs to be cut at specific sequences using restriction enzymes. These enzymes are produced by bacteria as mechanisms of innate immunity against intruding viral DNA and function as molecular scissors. Hence, after restriction enzymes identify a viral DNA, they start to break it apart by cutting it into segments at certain nucleotide sequences they recognize. These nucleotide sequences are often six to twelve nucleotides long and are generally palindromic, which means that they have the same nucleotide sequence in the 3&#8217;-5&#8217; and 5&#8217;-3&#8217; directions. For instance, the restriction enzyme EcoRI cuts DNA at the sequence 3&#8217;...GAATTC&#8230;-5&#8217;, which reads the same in the 5&#8217;-3&#8217; direction. Like EcoRI, there are hundreds of enzymes that correspond to many distinct palindromic sequences. Once DNA is cut by these enzymes, scientists can load the DNA onto a gel in an electrophoresis chamber and pass electrical current through the gel. DNA carries negative charges, which causes DNA fragments to migrate towards the anode. However, the pores of the gel slow down larger DNA fragments relative to smaller DNA sequences, thus the pieces separate according to their size. After the completion of the electrophoresis, DNA fragments can be visualized with the aid of dyes that specifically bind to DNA molecules.

Cutting DNA with restriction enzymes and separating DNA fragments with electrophoresis allows researchers to identify the sizes of unknown fragments relative to a standard ladder. These fragments of interest can then be further isolated and ligated into a plasmid vector for genetic cloning. Genetic engineering and laboratory analyses have been improved immensely with these methods. With DNA profiling, scientists are able to sequence genomes to further understand the workings of organisms and are also able to identify and characterize certain genes1.

DNA isolation and profiling are also practical for events directly impacting everyday life. For example, forensics scientists routinely analyze DNA samples to provide evidence for criminal and civil cases2. Similarly, healthcare workers extract and analyze DNA to check for paternity and genetic diseases. Recently, DNA ancestry analysis kits became popular by allowing users determine their genetic lineage, find relatives, and even discover their genetic disposition to various health conditions3. Finally, with advancements in biotechnology and genetic engineering, personalized medicine is gaining traction among clinical researchers to develop treatments by using an individual&#8217;s genetic data, paving the way to effectively treat patients without detrimental side effects4.

<h4>References</h4>

<ol class="references">
	<li>Chambers, GK, et al. DNA fingerprinting in zoology: past, present, future. Investig Genet. 2014, Vol. 5, 3 doi: 10.1186/2041-2223-5-3.</li>
	<li>Roewer, L. DNA fingerprinting in forensics: past, present, future. Investig Genet. . 2013, Vol. 4, 22 doi: 10.1186/2041-2223-4-22.</li>
	<li>Kirkpatrick, BE and Rashkin, MD. Ancestry Testing and the Practice of Genetic Counseling. J Gen Counseling. 2016, Vol. 26, 1 (6-20).</li>
	<li>Hamburg, MA and Collins, FS. The Path to Personalized Medicine. N Engl J Med . 2010; , Vol. 363, 301-304.</li>
</ol>

The revelation of DNA as the hereditary molecule in all organisms has led to enormous scientific and medical breakthroughs and significantly enhanced our ...