Name: using a fluorescent pcr-capillary gel electrophoresis technique to genotype crispr/cas9-mediated knockout mutants in a high-throughput format
Uploaded: 2017-04-08T14:00:00
Description: Watch this Scientific Journal Video about Using a Fluorescent PCR-capillary Gel Electrophoresis Technique to Genotype CRISPR/Cas9-mediated Knockout Mutants in a High-throughput Format at JoVE.com

The authors would like to thank Ms. Tan Shi Min, Ms. Helen Ong, and Dr. Zhao Yi for helping with the capillary gel electrophoresis experiments. This work was supported by NMRC/IRG grant NMRC/1314/2011 and MOE AcRF Tier 2 Fund grant MOE2011-T2-1-051.

1. Obtaining CRISPR/Cas9-targeted Single-cell Clones
<ol>
	<li>Seed HEPG2 cells on a 6-well plate at 500,000 cells per well in 2 mL of antibiotic-free Dulbecco&#39;s Modified Eagle Medium (DMEM) supplemented with 10% fetal bovine serum (FBS). Incubate for 24 h at 37 &#176;C and 5% CO2.</li>
	<li>Transfect cells with plasmid co-expressing Cas9 and specific sgRNA against the gene of interest using an appropriate transfection reagent as per the manufacturer&#39;s instructions. 
	NOTE: For example, sgRNA ca...

<ol>
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T., Li, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=High-throughput+genotyping+of+CRISPR/Cas9-mediated+mutants+using+fluorescent+PCR-capillary+gel+electrophoresis.">High-throughput genotyping of CRISPR/Cas9-mediated mutants using fluorescent PCR-capillary gel electrophoresis.</a> Sci. Rep. 5, 15587 (2015).</li><li>Liu, C. C., 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=Distinct+Responses+of+Stem+Cells+to+Telomere+Uncapping-A+Potential+Strategy+to+Improve+the+Safety+of+Cell+Therapy.">Distinct Responses of Stem Cells to Telomere Uncapping-A Potential Strategy to Improve the Safety of Cell Therapy.</a> Stem cells. 34, 2471-2484 (2016).</li><li>Doench, J. 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The knocking out of a specific gene in a model cell line of choice has become routine for elucidating the role that the gene plays in that particular cellular context. In fact, several genome-wide screens are currently available that use the CRISPR/Cas9 system to target virtually all known human genes in the genome14,15,16. With these large-scale screens (or even small-scale targeting of individual genes of interest), it is impo...

Reverse genetic approaches have allowed scientists to elucidate the effects of specific alterations in the genome on the cell or whole organism. For example, the expression of a particular gene can be attenuated by gene knockdown1,2 (partial reduction) or gene knockout3,4 (complete ablation) in order to determine the effect that this has on the function of the cell or on the development of the organism.
Gene knockout experiments have become easier since the introduction of sequence-specific programmable nucleases, such as zinc-finger nucleases (ZFNs) and transcription activator-like effector nucleases (TALENs). However, the relatively recent characterization of the clustered regularly interspersed short palindromic repeat (CRISPR)/Cas9 system has made it extremely easy for any laboratory around the world to perform gene knockout experiments. In essence, the CRISPR/Cas9 system consists of two essential components-a single guide RNA (sgRNA), which recognizes and binds via base complementarity to a specific sequence in the genome, and an endonuclease called Cas9. The aftermath of the specific binding and action of the sgRNA-Cas9 complex on genomic DNA is the double-strand cleavage of DNA. This, in turn, triggers the DNA damage response mechanism in the cell, which is subsequently repaired via the non-homologous end-joining (NHEJ) or homologous recombination (HR) pathways. Since the NHEJ repair mechanism (but not the HR mechanism) often results in the random insertion or deletion of nucleotides at the site of repair, resulting in insertion/deletion (indel) mutations, it may cause the reading frame of an exon to shift. This may then result in the knockout of the gene due to premature termination of translation and nonsense-mediated decay5,6,7.
Despite the convenience afforded by the introduction of the CRISPR/Cas9 system in knocking out a gene, the genotyping of clones of targeted cells remains a bottleneck, especially in a high-throughput setting8,9. Existing techniques either suffer major inherent limitations or are financially costly. For example, the SURVEYOR or T7E1 assay, which is an enzymatic assay that detects mismatches in DNA duplexes10, is not able to distinguish between wildtype clones and homozygous mutants (clones whose alleles are mutated identically), since these clones have identical alleles and thus do not present mismatches in their DNA sequence11. In addition, the use of Sanger sequencing, which is considered the gold standard in genotyping mutant clones, in a high-throughput setup is undesirable due to its high cost. Here, we present a detailed protocol of the fluorescent PCR-capillary gel electrophoresis technique, which can circumvent the limitations of the other existing genotyping techniques and is particularly useful in performing a high-throughput screen of nuclease-mediated knockout clones. This method is technically simple to perform and saves time and cost.

<table border="0" cellpadding="0" cellspacing="0" width="1548">
	<colgroup>
		<col />
		<col />
		<col />
		<col />
	</colgroup>
	<tbody>
		<tr height="20">
			<td height="20" style="height:20px;width:401px;">HEPG2 cells</td>
			<td style="width:196px;">ATCC</td>
			<td style="width:135px;">HB-8065</td>
			<td style="width:816px;"></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">HyClone Dulbecco&#39;s Modified Eagles Medium (DMEM)</td>
			<td>Thermo Fisher Scientific</td>
			<td>SH30022.01</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">HyClone Fetal Bovine Serum</td>
			<td>Thermo Fisher Scientific</td>
			<td>SV30160.03</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">pSpCas9(BB)-2A-GFP plasmid</td>
			<td>Addgene</td>
			<td>PX458</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Lipofectamine 2000</td>
			<td>Thermo Fisher Scientific</td>
			<td>11668027</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Trypsin-EDTA (0.25%), phenol red</td>
			<td>Thermo Fisher Scientific</td>
			<td>25200056</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Trypsin-EDTA (0.5%), no phenol red</td>
			<td>Thermo Fisher Scientific</td>
			<td>15400054</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Penicillin-Streptomycin (10,000 U/mL)</td>
			<td>Thermo Fisher Scientific</td>
			<td>15140122</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">HyClone Water, Molecular Biology Grade</td>
			<td>GE Healthcare</td>
			<td>SH30538.02</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">CRISPR sgRNA insert oligonucleotide (sense)</td>
			<td>AITbiotech</td>
			<td>None</td>
			<td>Sequence: 5&#39;-CACCGCTAACCTTTCAGCCTGCCTA-3&#39;</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">CRISPR sgRNA insert oligonucleotide (anti-sense)</td>
			<td>AITbiotech</td>
			<td>None</td>
			<td>Sequence: 5&#39;-AAACTAGGCAGGCTGAAAGGTTAGC-3&#39;</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Unlabeled PCR amplification forward primer</td>
			<td>AITbiotech</td>
			<td>None</td>
			<td>Sequence: 5&#39;-CACTAACTCCAATGCTTCAGTTTC-3&#39;; this primer is also used to sequence PCR amplified alleles</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">6-FAM-labeled fluorescent PCR forward primer</td>
			<td>AITbiotech</td>
			<td>None</td>
			<td>Sequence: 5&#39;-6-FAM-CACTAACTCCAATGCTTCAGTTTC-3&#39;</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">HEX-labeled fluorescent PCR forward primer</td>
			<td>AITbiotech</td>
			<td>None</td>
			<td>Sequence: 5&#39;-HEX-CACTAACTCCAATGCTTCAGTTTC-3&#39;</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Unlabeled PCR reverse primer</td>
			<td>AITbiotech</td>
			<td>None</td>
			<td>Sequence: 5&#39;-CCTCTTCCAAGTCTGCTTATGT-3&#39;</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Taq PCR Core Kit</td>
			<td>QIAGEN</td>
			<td>201223</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Hi-Di Formamide</td>
			<td>Thermo Fisher Scientific</td>
			<td>4311320</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">GeneScan 500 LIZ Dye Size Standard</td>
			<td>Thermo Fisher Scientific</td>
			<td>4322682</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">MicroAmp Optical 96-Well Reaction Plate</td>
			<td>Thermo Fisher Scientific</td>
			<td>4306737</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">3500xL Genetic Analyzer</td>
			<td>Thermo Fisher Scientific</td>
			<td>4405633</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">3500 Series 2 program</td>
			<td>Thermo Fisher Scientific</td>
			<td>4476988</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Gene Mapper 5 program</td>
			<td>Thermo Fisher Scientific</td>
			<td>4475073</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Gentra Puregene Cell Kit</td>
			<td>QIAGEN</td>
			<td>1045696</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Wizard SV Gel and PCR Clean-Up System</td>
			<td>Promega</td>
			<td>A9282</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">NAP1L1 Antibody (N-term)</td>
			<td>Abgent</td>
			<td>AP1920b</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Nuclear Matrix Protein p84 antibody [5E10]</td>
			<td>GeneTex</td>
			<td>GTX70220</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Peroxidase AffiniPure Goat Anti-Rabbit IgG</td>
			<td>Jackson ImmunoResearch</td>
			<td>111-035-144</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Peroxidase AffiniPure Sheep Anti-Mouse IgG</td>
			<td>Jackson ImmunoResearch</td>
			<td>515-035-003</td>
			<td></td>
		</tr>
	</tbody>
</table>

using a fluorescent pcr-capillary gel electrophoresis technique to genotype crispr/cas9-mediated knockout mutants in a high-throughput format

The development of programmable genome-editing tools has facilitated the use of reverse genetics to understand the roles specific genomic sequences play in the functioning of cells and whole organisms. This cause has been tremendously aided by the recent introduction of the CRISPR/Cas9 system-a versatile tool that allows researchers to manipulate the genome and transcriptome in order to, among other things, knock out, knock down, or knock in genes in a targeted manner. For the purpose of knocking out a gene, CRISPR/Cas9-mediated double-strand breaks recruit the non-homologous end-joining DNA repair pathway to introduce the frameshift-causing insertion or deletion of nucleotides at the break site. However, an individual guide RNA may cause undesirable off-target effects, and to rule these out, the use of multiple guide RNAs is necessary. This multiplicity of targets also means that a high-volume screening of clones is required, which in turn begs the use of an efficient high-throughput technique to genotype the knockout clones. Current genotyping techniques either suffer from inherent limitations or incur high cost, hence rendering them unsuitable for high-throughput purposes. Here, we detail the protocol for using fluorescent PCR, which uses genomic DNA from crude cell lysate as a template, and then resolving the PCR fragments via capillary gel electrophoresis. This technique is accurate enough to differentiate one base-pair difference between fragments and hence is adequate in indicating the presence or absence of a frameshift in the coding sequence of the targeted gene. This precise knowledge effectively precludes the need for a confirmatory sequencing step and allows users to save time and cost in the process. Moreover, this technique has proven to be versatile in genotyping various mammalian cells of various tissue origins targeted by guide RNAs against numerous genes, as shown here and elsewhere.

The fluorescent PCR-capillary gel electrophoresis technique described here is anticipated to be applicable to any targetable region in the genome in virtually any cell line that is amenable to foreign DNA delivery. We have previously demonstrated its application by targeting three genes in a colorectal cancer cell line12. Here, we show its efficacy in genotyping a hepatocellular carcinoma cell line, HEPG2, targeted with a CRISPR/Cas9 construct against the Nucleosom...

Watch this Scientific Journal Video about Using a Fluorescent PCR-capillary Gel Electrophoresis Technique to Genotype CRISPR/Cas9-mediated Knockout Mutants in a High-throughput Format at JoVE.com

Using a Fluorescent PCR-capillary Gel Electrophoresis Technique to Genotype CRISPR/Cas9-mediated Knockout Mutants in a High-throughput Format

The genotyping technique described here, which couples fluorescent polymerase chain reaction (PCR) to capillary gel electrophoresis, allows for high-throughput genotyping of nuclease-mediated knockout clones. It circumvents limitations faced by other genotyping techniques and is more cost effective than sequencing methods.

The development of programmable genome-editing tools has facilitated the use of reverse genetics to understand the roles specific genomic sequences play ...

The overall goal of this technique is to genotype CRISPR/Cas9 induced insertion deletion mutant clones in a high-throughput manner. This method can help answer key questions in the genetics field, such as the phenotypic effect of knocking out a particular gene in a SAIL model of choice. The main advantage of this technique is there is a minimal to high throughput screening that is multiflexible.Though this method can provide insight into human cancer genetics, it can also be applied to the other systems, such as human, stem, and the primary cell, or the cells of non human origin. We first had the idea for this method when we performed short tandem repeats or STR typing assays. To begin the procedure, transfect the chosen cells with a plasmid, co expressing a fluorescent label cas9 and the single guide RNA.Trypsinize the cells and select about 3, 500 fluorescently labeled clones. Plate the clones in portions of 500, 1, 000, and 2, 000 cells on 10 centimeter dishes in eight milliliters of penicillin streptomycin supplemented growth medium. Incubate the cells in 5%co2 atmosphere at 37 degrees celsius, replacing the medium every five days until single cell colonies are visible to the naked eye.Then aspirate individual colonies into a 200 microliter pipette with about five microliters of growth medium. Transfer each colony to a separate well containing 200 microliters of growth medium. Repeatedly pipette each mixture up and down to re suspend the cells.Incubate the cells under the previously described conditions until the cells reach 50 to 90%confluence. Remove excess culture medium from the wells, and add 25 microliters of 0.05%trypsin EDTA without phenol red to each well. Incubate the cells at 37 degrees celsius for 7 minutes.Then repeatedly pipette the mixtures up and down to re suspend the trypsinized cells. Inspect the wells under a microscope to verify that the cells have detached from the well walls. To prepare replicates of the individual clones, transfer five microliters of each cell suspension to an empty 96 well culture plate.Add 200 microliters of growth medium to each well. Then load the wells of an empty 96 well PCR plate with 10 microliters of lysis buffer. Transfer another five microliters of each cell suspension to this 96 well plate.Briefly centrifuge the plate until the liquid settles in the bottom of the wells. Add 200 microliters of growth medium to the remaining 15 microliters of each cell suspension. Store the original suspension and the replicates under the incubation conditions for later verification of the knockout status of the clones.Then use thermal cycling to completely lyse the cells in lysis buffer. Briefly centrifuge the lysates. Dilute the lysates with 40 microliters of nuclease free water.Vortex and briefly centrifuge the diluted lysates. Before performing fluorescent PCR, design and test the specificity of several pairs of unlabeled primers on lysed wild-type cells. Identify the optimal primer pair and obtain the fluorophore labeled forward primers and the unlabeled reverse primer.Be sure to test the specificity of the primers using vortex cells, lyse using the homemade lysis buffer, as results may vary from using purified genomic DNA. Using the labeled primers, perform 20 microliter fluorescent PCR reactions with three microliters of the diluted lysates to amplify the target regions. Assess the size and relative quantities of the PCR amplicons by resolving five microliters of the amplicons on a 1%agarose gel.To begin sample preparation, use nuclease free water to dilute amplicons of wild-type and CRISPR/Cas9 targeted DNA to an approximate concentration of 2.5 nanograms per microliter. Mix together equal volumes of the diluted wild-type and targeted DNA samples. Load the wells of a 96 well PCR plate with nine microliters of a 29 to one mixture of deionized formamide and dye labeled size standard and one microliter of the mixed amplicons.Seal the plate tightly and heat the samples at 95 degrees celsius for three minutes with a PCR thermocycler. Immediately after heating, cool the plate on ice for three minutes. Perform capillary gel electrophoresis with a genetic analyzer.After electrophoresis is complete, import the data into analysis software and plot the data. Verify the quality of the size standard by reviewing the data in the appropriate dye channel. Then export the dye channel values for the un targeted wild-type controls and targeted clones in txt format.From this file, import the dye identities, sample file names, fragment sizes, and peak height values into spreadsheet software. Calculate the difference in fragment size between the targeted clone and the un targeted wild type control in each sample. Identify the clones with indel mutations that are not multiples of three base pairs.Serially expand the selected clones from the stored replicates. Perform Sanger sequencing and western blood analysis to determine the clone genotypes and verify the knockout status of the clones. The hepatocellular carcinoma cell line HEPG2 was targeted with a CRISPR/Cas9 construct against the Nap1L1 gene.The un targeted wild-type alleles and the CRISPR/Cas9 targeted alleles were PCR amplified using primers labeled with green and blue fluorophores, respectively. By using a specifically optimized fluorescent PCR protocol, the amplicons of the targeted clones were obtained in good yield. No interference was observed between the green and blue fluorescent dyes within samples of individual clones.Analysis of the fragment sizes, determined from capillary gel electrophoresis, revealed the deletion of one and 10 base pairs from the two clones shown here. Sanger sequencing results were consistent with the capillary gel electrophoresis analysis. Western blood analysis confirmed that the selected clones did not express NAP1L1.While attempting this procedure it's important to remember to label your samples carefully, as there are many samples involved, and also to minimize the exposure time of your fluorophore label amplicon as they are light sensitive. Following this procedure, other methods like quantative RT PCR, western blood analysis, and the Sanger sequencing can be performed in order to answer additional questions like what are the genes of interest, is completely knocked out. After watching this video you should have a good understanding of how to genotype CRISPR/Cas9 induced mutant clones in a high-throughput manner using fluorescent PCR coupled to capillary gel electrophoresis.

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Research

JoVE Journal

Genetics

Perturbations of Circulating miRNAs in Irritable Bowel Syndrome Detected Using a Multiplexed High-throughput Gene Expression Platform

The gene expression platform assay allows for robust and highly reproducible quantification of the expression of up to 800 transcripts (mRNA or miRNAs) in a single reaction. The miRNA assay counts transcripts by directly imaging and digitally counting miRNA molecules that are labeled with color-coded fluorescent barcoded probe sets (a reporter probe and a capture probe). Barcodes are hybridized directly to mature miRNAs that have been elongated by ligating a unique oligonucleotide tag (miRtag) to the 3&#39; end. Reverse transcription and amplification of the transcripts are not required. Reporter probes contain a sequence of six color positions populated using a combination of four fluorescent colors. The four colors over six positions are used to construct a gene-specific color barcode sequence. Post-hybridization processing is automated on a robotic prep station. After hybridization, the excess probes are washed away, and the tripartite structures (capture probe-miRNA-reporter probe) are fixed to a streptavidin-coated slide via the biotin-labeled capture probe. Imaging and barcode counting is done using a digital analyzer. The immobilized barcoded miRNAs are visualized and imaged using a microscope and camera, and the unique barcodes are decoded and counted. Data quality control (QC), normalization, and analysis are facilitated by a custom-designed data processing and analysis software that accompanies the assay software. The assay demonstrates high linearity over a broad range of expression, as well as high sensitivity. Sample and assay preparation does not involve enzymatic reactions, reverse transcription, or amplification; has few steps; and is largely automated, reducing investigator effects and resulting in high consistency and technical reproducibility. Here, we describe the application of this technology to identifying circulating miRNA perturbations in irritable bowel syndrome.

We describe the use of a multiplexed high-throughput gene expression platform that quantitates gene expression by barcoding and counting molecules in biological substrates without the need for amplification. We used the platform to quantitate microRNA (miRNA) expression in whole blood in subjects with and without irritable bowel syndrome.

The gene expression platform assay allows for robust and highly reproducible quantification of the expression of up to 800 transcripts (mRNA or miRNAs) in ...

High-Throughput Robotically Assisted Isolation of Temperature-sensitive Lethal Mutants in Chlamydomonas reinhardtii

Systematic identification and characterization of genetic perturbations have proven useful to decipher gene function and cellular pathways. However, the conventional approaches of permanent gene deletion cannot be applied to essential genes. We have pioneered a unique collection of ~70 temperature-sensitive (ts) lethal mutants for studying cell cycle regulation in the unicellular green algae Chlamydomonas reinhardtii1. These mutations identify essential genes, and the ts alleles can be conditionally inactivated by temperature shift, providing valuable tools to identify and analyze essential functions. Mutant collections are much more valuable if they are close to comprehensive, since scattershot collections can miss important components. However, this requires the efficient collection of a large number of mutants, especially in a wide-target screen. Here, we describe a robotics-based pipeline for generating ts lethal mutants and analyzing their phenotype in Chlamydomonas. This technique can be applied to any microorganism that grows on agar. We have collected over 3000 ts mutants, probably including mutations in most or all cell-essential pathways, including about 200 new candidate cell cycle mutations. Subsequent molecular and cellular characterization of these mutants should provide new insights in plant cell biology; a comprehensive mutant collection is an essential prerequisite to ensure coverage of a broad range of biological pathways. These methods are integrated with downstream genetics and bioinformatics procedures for efficient mapping and identification of the causative mutations that are beyond the scope of this manuscript.

High-Throughput Robotically Assisted Isolation of Temperature-sensitive Lethal Mutants in Chlamydomonas reinhardtii

Temperature-sensitive (ts) lethal mutants are valuable tools to identify and analyze essential functions. Here we describe methods to generate and classify ts lethal mutants in high throughput.

Systematic identification and characterization of genetic perturbations have proven useful to decipher gene function and cellular pathways. However, the ...

Selection-dependent and Independent Generation of CRISPR/Cas9-mediated Gene Knockouts in Mammalian Cells

The CRISPR/Cas9 genome engineering system has revolutionized biology by allowing for precise genome editing with little effort. Guided by a single guide RNA (sgRNA) that confers specificity, the Cas9 protein cleaves both DNA strands at the targeted locus. The DNA break can trigger either non-homologous end joining (NHEJ) or homology directed repair (HDR). NHEJ can introduce small deletions or insertions which lead to frame-shift mutations, while HDR allows for larger and more precise perturbations. Here, we present protocols for generating knockout cell lines by coupling established CRISPR/Cas9 methods with two options for downstream selection/screening. The NHEJ approach uses a single sgRNA cut site and selection-independent screening, where protein production is assessed by dot immunoblot in a high-throughput manner. The HDR approach uses two sgRNA cut sites that span the gene of interest. Together with a provided HDR template, this method can achieve deletion of tens of kb, aided by the inserted selectable resistance marker. The appropriate applications and advantages of each method are discussed.

Recent advances in the ability to genetically manipulate somatic cell lines hold great potential for basic and applied research. Here, we present two approaches for CRISPR/Cas9 generated knockout production and screening in mammalian cell lines, with and without the use of selectable markers.

The CRISPR/Cas9 genome engineering system has revolutionized biology by allowing for precise genome editing with little effort. Guided by a single guide ...

G2-seq: A High Throughput Sequencing-based Technique for Identifying Late Replicating Regions of the Genome

Numerous techniques have been developed to follow the progress of DNA replication through the S phase of the cell cycle. Most of these techniques have been directed toward elucidation of the location and timing of initiation of genome duplication rather than its completion. However, it is critical that we understand regions of the genome that are last to complete replication, because these regions suffer elevated levels of chromosomal breakage and mutation, and they have been associated with both disease and aging. Here we describe how we have extended a technique that has been used to monitor replication initiation to instead identify those regions of the genome last to complete replication. This approach is based on a combination of flow cytometry and high throughput sequencing. Although this report focuses on the application of this technique to yeast, the approach can be used with any cells that can be sorted in a flow cytometer according to DNA content.

We describe a technique for combining flow cytometry and high throughput sequencing to identify late replicating regions of the genome.

Numerous techniques have been developed to follow the progress of DNA replication through the S phase of the cell cycle. Most of these techniques have ...

Robust DNA Isolation and High-throughput Sequencing Library Construction for Herbarium Specimens

Herbaria are an invaluable source of plant material that can be used in a variety of biological studies. The use of herbarium specimens is associated with a number of challenges including sample preservation quality, degraded DNA, and destructive sampling of rare specimens. In order to more effectively use herbarium material in large sequencing projects, a dependable and scalable method of DNA isolation and library preparation is needed. This paper demonstrates a robust, beginning-to-end protocol for DNA isolation and high-throughput library construction from herbarium specimens that does not require modification for individual samples. This protocol is tailored for low quality dried plant material and takes advantage of existing methods by optimizing tissue grinding, modifying library size selection, and introducing an optional reamplification step for low yield libraries. Reamplification of low yield DNA libraries can rescue samples derived from irreplaceable and potentially valuable herbarium specimens, negating the need for additional destructive sampling and without introducing discernible sequencing bias for common phylogenetic applications. The protocol has been tested on hundreds of grass species, but is expected to be adaptable for use in other plant lineages after verification. This protocol can be limited by extremely degraded DNA, where fragments do not exist in the desired size range, and by secondary metabolites present in some plant material that inhibit clean DNA isolation. Overall, this protocol introduces a fast and comprehensive method that allows for DNA isolation and library preparation of 24 samples in less than 13 h, with only 8 h of active hands-on time with minimal modifications.

This article demonstrates a detailed protocol for DNA isolation and high-throughput sequencing library construction from herbarium material including rescue of exceptionally poor-quality DNA.

Herbaria are an invaluable source of plant material that can be used in a variety of biological studies. The use of herbarium specimens is associated with ...

CRISPR/Cas9-mediated Targeted Integration In Vivo Using a Homology-mediated End Joining-based Strategy

As a promising genome editing platform, the CRISPR/Cas9 system has great potential for efficient genetic manipulation, especially for targeted integration of transgenes. However, due to the low efficiency of homologous recombination (HR) and various indel mutations of non-homologous end joining (NHEJ)-based strategies in non-dividing cells, in vivo genome editing remains a great challenge. Here, we describe a homology-mediated end joining (HMEJ)-based CRISPR/Cas9 system for efficient in vivo precise targeted integration. In this system, the targeted genome and the donor vector containing homology arms (~800 bp) flanked by single guide RNA (sgRNA) target sequences are cleaved by CRISPR/Cas9. This HMEJ-based strategy achieves efficient transgene integration in mouse zygotes, as well as in hepatocytes in vivo. Moreover, a HMEJ-based strategy offers an efficient approach for correction of fumarylacetoacetate hydrolase (Fah) mutation in the hepatocytes and rescues Fah-deficiency induced liver failure mice. Taken together, focusing on targeted integration, this HMEJ-based strategy provides a promising tool for a variety of applications, including generation of genetically modified animal models and targeted gene therapies.

CRISPR/Cas9-mediated Targeted Integration In Vivo Using a Homology-mediated End Joining-based Strategy

The clustered regularly interspaced short palindromic repeats/CRISPR associated protein 9 (CRISPR/Cas9) system provides a promising tool for genetic engineering, and opens up the possibility of targeted integration of transgenes. We describe a homology-mediated end joining (HMEJ)-based strategy for efficient DNA targeted integration in vivo and targeted gene therapies using CRISPR/Cas9.

As a promising genome editing platform, the CRISPR/Cas9 system has great potential for efficient genetic manipulation, especially for targeted integration ...

A Protocol for the Production of Integrase-deficient Lentiviral Vectors for CRISPR/Cas9-mediated Gene Knockout in Dividing Cells

Lentiviral vectors are an ideal choice for delivering gene-editing components to cells due to their capacity for stably transducing a broad range of cells and mediating high levels of gene expression. However, their ability to integrate into the host cell genome enhances the risk of insertional mutagenicity and thus raises safety concerns and limits their usage in clinical settings. Further, the persistent expression of gene-editing components delivered by these integration-competent lentiviral vectors (ICLVs) increases the probability of promiscuous gene targeting. As an alternative, a new generation of integrase-deficient lentiviral vectors (IDLVs) has been developed that addresses many of these concerns. Here the production protocol of a new and improved IDLV platform for CRISPR-mediated gene editing and list the steps involved in the purification and concentration of such vectors is described and their transduction and gene-editing efficiency using HEK-293T cells was demonstrated. This protocol is easily scalable and can be used to generate high titer IDLVs that are capable of transducing cells in vitro and in vivo. Moreover, this protocol can be easily adapted for the production of ICLVs.

We describe the production strategy of integrase-deficient lentiviral vectors (IDLVs) as vehicles for delivering CRISPR/Cas9 to cells. With an ability to mediate quick and robust gene editing in cells, IDLVs present a safer and equally effective vector platform for gene delivery compared to integrase-competent vectors.

Lentiviral vectors are an ideal choice for delivering gene-editing components to cells due to their capacity for stably transducing a broad range of cells ...

High-throughput Identification of Synergistic Drug Combinations by the Overlap2 Method

Although antimicrobial drugs have dramatically increased the lifespan and quality of life in the 20th century, antimicrobial resistance threatens our entire society's ability to treat systemic infections. In the United States alone, antibiotic-resistant infections kill approximately 23,000 people a year and cost around 20 billion USD in additional healthcare. One approach to combat antimicrobial resistance is combination therapy, which is particularly useful in the critical early stage of infection, before the infecting organism and its drug resistance profile have been identified. Many antimicrobial treatments use combination therapies. However, most of these combinations are additive, meaning that the combined efficacy is the same as the sum of the individual antibiotic efficacy. Some combination therapies are synergistic: the combined efficacy is much greater than additive. Synergistic combinations are particularly useful because they can inhibit the growth of antimicrobial drug resistant strains. However, these combinations are rare and difficult to identify. This is due to the sheer number of molecules needed to be tested in a pairwise manner: a library of 1,000 molecules has 1 million potential combinations. Thus, efforts have been made to predict molecules for synergy. This article describes our high-throughput method for predicting synergistic small molecule pairs known as the Overlap2 Method (O2M). O2M uses patterns from chemical-genetic datasets to identify mutants that are hypersensitive to each molecule in a synergistic pair but not to other molecules. The Brown lab exploits this growth difference by performing a high-throughput screen for molecules that inhibit the growth of mutant but not wild-type cells. The lab's work previously identified molecules that synergize with the antibiotic trimethoprim and the antifungal drug fluconazole using this strategy. Here, the authors present a method to screen for novel synergistic combinations, which can be altered for multiple microorganisms.

High-throughput Identification of Synergistic Drug Combinations by the Overlap2 Method

Synergistic drug combinations are difficult and time-consuming to identify empirically. Here, we describe a method for identifying and validating synergistic small molecules.

Although antimicrobial drugs have dramatically increased the lifespan and quality of life in the 20th century, antimicrobial resistance threatens our ...

A Rapid and Facile Pipeline for Generating Genomic Point Mutants in C. elegans Using CRISPR/Cas9 Ribonucleoproteins

The clustered regularly interspersed palindromic repeats (CRISPR)-CRISPR-associated protein 9 (Cas9) prokaryotic adaptive immune defense system has been co-opted as a powerful tool for precise eukaryotic genome engineering. Here, we present a rapid and simple method using chimeric single guide RNAs (sgRNA) and CRISPR-Cas9 Ribonucleoproteins (RNPs) for the efficient and precise generation of genomic point mutations in C. elegans. We describe a pipeline for sgRNA target selection, homology-directed repair (HDR) template design, CRISPR-Cas9-RNP complexing and delivery, and a genotyping strategy that enables the robust and rapid identification of correctly edited animals. Our approach not only permits the facile generation and identification of desired genomic point mutant animals, but also facilitates the detection of other complex indel alleles in approximately 4 - 5 days with high efficiency and a reduced screening workload.

A Rapid and Facile Pipeline for Generating Genomic Point Mutants in C. elegans Using CRISPR/Cas9 Ribonucleoproteins

Here, we present a method to engineer the genome of C. elegans using CRISPR-Cas9 ribonucleoproteins and homology dependent repair templates.

The clustered regularly interspersed palindromic repeats (CRISPR)-CRISPR-associated protein 9 (Cas9) prokaryotic adaptive immune defense system has been ...

Digital PCR-based Competitive Index for High-throughput Analysis of Fitness in Salmonella

A competitive index is a common method used to assess bacterial fitness and/or virulence. The utility of this approach is exemplified by its ease to perform and its ability to standardize the fitness of many strains to a wild-type organism. The technique is limited, however, by available phenotypic markers and the number of strains that can be assessed simultaneously, creating the need for a great number of replicate experiments. Concurrent with large numbers of experiments, the labor and material costs for quantifying bacteria based on phenotypic markers are not insignificant. To overcome these negative aspects while retaining the positive aspects, we have developed a molecular-based approach to directly quantify microorganisms after engineering genetic markers onto bacterial chromosomes. Unique, 25 base pair DNA barcodes were inserted at an innocuous locus on the chromosome of wild-type and mutant strains of Salmonella. In vitro competition experiments were performed using inocula consisting of pooled strains. Following the competition, the absolute numbers of each strain were quantified using digital PCR and the competitive indices for each strain were calculated from those values. Our data indicate that this approach to quantifying Salmonella is extremely sensitive, accurate, and precise for detecting both highly abundant (high fitness) and rare (low fitness) microorganisms. Additionally, this technique is easily adaptable to nearly any organism with chromosomes capable of modification, as well as to various experimental designs that require absolute quantification of microorganisms.

Digital PCR-based Competitive Index for High-throughput Analysis of Fitness in Salmonella

This molecular-based approach for determining bacterial fitness facilitates precise and accurate detection of microorganisms using unique genomic DNA barcodes that are quantified via digital PCR. The protocol describes calculating the competitive index for Salmonella strains; however, the technology is readily adaptable to protocols requiring absolute quantification of any genetically-malleable organism.

A competitive index is a common method used to assess bacterial fitness and/or virulence. The utility of this approach is exemplified by its ease to ...