Name: selection-dependent and independent generation of crispr/cas9-mediated gene knockouts in mammalian cells
Uploaded: 2017-06-16T15:00:00
Description: Watch this Scientific Journal Video about Selection-dependent and Independent Generation of CRISPR/Cas9-mediated Gene Knockouts in Mammalian Cells at JoVE.com

The authors would like to acknowledge Gissell Sanchez, Megan Lee, and Jason Estep for experimental assistance, and Weifeng Gu and Xuemei Chen for sharing reagents.

1. Identification of Homology Regions Around the Desired Deletion
NOTE: Only necessary if using selection-based editing.
<ol>
	<li>Select two regions, initially 1.5-2 kb, on either side of the desired deletion locus, which will serve as homology arms in the HDR template (Figure 1A). Identify regions that lack BsaI recognition sites on either strand (GGTCTC) to facilitate cloning. If BsaI sites are unavoidable, use an alternate type IIs restriction enzyme (BsmBI,...

<ol>
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E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cell+cycle+and+genetic+requirements+of+two+pathways+of+nonhomologous+end-joining+repair+of+double-strand+breaks+in+Saccharomyces+cerevisiae.">Cell cycle and genetic requirements of two pathways of nonhomologous end-joining repair of double-strand breaks in Saccharomyces cerevisiae.</a> Mol Cell Biol. 16 (5), 2164-2173 (1996).</li><li>Liang, F., Han, M., Romanienko, P. J., Jasin, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Homology-directed+repair+is+a+major+double-strand+break+repair+pathway+in+mammalian+cells.">Homology-directed repair is a major double-strand break repair pathway in mammalian cells.</a> Proc Natl Acad Sci U S A. 95 (9), 5172-5177 (1998).</li><li>Gratz, S. 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The CRISPR/Cas9 system has allowed for efficient generation of stable genomic modifications, which provide a more consistent alternative to other transient manipulation methods. Here, we have presented two methods for rapid identification of CRISPR/Cas9 gene knockouts in mammalian cell lines. Both methods require little cellular material, so testing can be done in early stages of clonal culture, saving time and reagents. To increase the efficiency of both methods, we recommend testing multiple sgRNAs, as efficiencies var...

Stable genetic alterations provide an advantage over transient methods of cellular perturbation, which can be variable in their efficiency and duration. Genomic editing has become increasingly common in recent years due to the development of target specific nucleases, such as zinc-finger nucleases1,2,3,4,5, transcription activator-like effector nucleases (TALENs)6,7,8,9 and RNA-guided nucleases derived from the clustered, regularly interspaced short palindromic repeats (CRISPR) system10.
The CRISPR/Cas9 editing machinery is adapted from an immune system that bacteria and archaea use to defend against viral infections11,12,13. In this process, short, 20-30 nt fragments of invading viral sequence are incorporated into a genomic locus as &#34;spacers&#34; flanked by repeating units14,15. Subsequent transcription and RNA processing generates small CRISPR-associated RNAs16 (crRNAs) that, together with a trans-activating crRNA17 (tracrRNA), assemble with the effector Cas9 endonuclease. The crRNAs thus provide specificity to Cas9 targeting, guiding the complex to cleave complementary viral DNA sequences and preventing further infections18,19. Any &#34;protospacer&#34; sequence in the targeted DNA can serve as the source of the crRNA, as long as it is directly 5&#39; to a short protospacer adjacent motif (PAM), NGG in the case of S. pyogenes Cas920. The absence of the PAM sequence near the spacer in the host&#39;s CRISPR locus distinguishes between self and non-self, preventing targeting of the host. Because of its universality and flexibility, this biological system has been powerfully adapted for genomic editing, such that nearly any PAM-adjacent DNA site can be targeted. In this version, a further modification fused the crRNA and tracrRNA into a single guide RNA (sgRNA) component that is loaded into the Cas9 protein21.
Upon expression of Cas9 and an sgRNA in eukaryotic cells, the Cas9 protein cleaves both DNA strands at the targeted locus. In the absence of a suitable region of homologous sequence, the cell fixes this break via non-homologous end joining (NHEJ)22,23,24, which typically introduces small deletions or, rarely, insertions. When targeting an open reading frame, the repair likely leads to a translational frameshift that produces a non-functional protein product. In contrast, when provided with an exogenous template with large regions of homology, the cell may fix the double-strand break by homology directed repair25,26. This route allows for larger precise deletions, replacements or insertions in the genome, coupled with the introduction of excisable selection markers27.
Here, we present protocols for generating knockout cell lines by either of these two CRISPR/Cas9 methods (Figure 1A). The NHEJ approach uses a single sgRNA cut site and selection-independent screening, and thus requires little upfront preparation. When using this method, guide RNAs complementary to exons near the 5&#39; end of the transcript, which are most likely to produce a knockout, must be designed. Since the modifications to the genome in this case are small, screening for knockout clones is based on dot blots, where the protein product is assessed in a high-throughput manner. We use the generation of ELAV-like 1 protein (ELAVL1) knockout lines as an example. The second approach relies on homology directed repair (HDR) and uses two sgRNA cut sites that span the gene or region of interest, allowing for deletions of tens of kb. A plasmid with two regions of homology that flank the cleavage sites provides a replacement template (Figure 1B), introducing a selectable resistance marker that increases efficiency of knockout generation. This method can also be adapted to introduce gene modifications with properly designed homology arms. In this case, the integration of a new DNA fragment allows for PCR based screening (Figure 1C). Here, we use the generation of Pumilio RNA binding family member 2 (PUM2) knockout lines as an example.

<table border="0" cellpadding="0" cellspacing="0" width="740">
	<tbody>
		<tr height="20">
			<td height="20" style="height:20px;width:227px;">Competent E. coli cells</td>
			<td style="width:95px;"></td>
			<td style="width:120px;"></td>
			<td style="width:299px;"></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">plasmid prep kit</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">pSpCas9(BB) plasmid</td>
			<td>Addgene</td>
			<td>42230</td>
			<td>Ran et al 2013, cloning sgRNAs</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">BbsI enzyme</td>
			<td>ThermoFisher</td>
			<td>FD1014</td>
			<td>Ran et al 2013, cloning sgRNAs</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">T7 DNA ligase</td>
			<td>NEB</td>
			<td>M0318L</td>
			<td>Ran et al 2013, cloning sgRNAs</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Tango Buffer</td>
			<td>ThermoFisher</td>
			<td>BY5</td>
			<td>Ran et al 2013, cloning sgRNAs</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">PlasmidSafe exonuclease</td>
			<td>Epicentre</td>
			<td>E3105K</td>
			<td>Ran et al 2013, cloning sgRNAs</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Q5 hot start high fidelity polymerase</td>
			<td>NEB</td>
			<td>M0494A</td>
			<td>HA amplification</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">pUC19-BsaI</td>
			<td></td>
			<td></td>
			<td>Modified pUC19 plasmid, mutated existing BsaI site and inserted two outward facing BsaI sites after BamHI/EcoRI digestion</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">pGolden-Neo</td>
			<td>Addgene</td>
			<td>51422</td>
			<td>Resistance cassette</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">pGolden-Hygro</td>
			<td>Addgene</td>
			<td>51423</td>
			<td>Resistance cassette</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">BsaI enzyme</td>
			<td>NEB</td>
			<td>R3535S</td>
			<td>Homology arm contruction</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">T7 DNA ligase</td>
			<td>NEB</td>
			<td>M0318L</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">PlasmidSafe exonuclease</td>
			<td>Epicentre</td>
			<td>E3105K</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Toothpicks</td>
			<td></td>
			<td></td>
			<td>bacterial PCR</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Taq polymerase</td>
			<td></td>
			<td></td>
			<td>bacterial colony PCR</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">HEK293 human cells</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">DMEM</td>
			<td>Corning</td>
			<td>10-013-CV</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">FBS</td>
			<td>Corning</td>
			<td>MT35010CV</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Penicillin-Strep (opt.)</td>
			<td>Gibco</td>
			<td>15140-122</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">6 well plates</td>
			<td>BioLite</td>
			<td>12556004</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">TransIT-LTI Transfection Reagent</td>
			<td>Mirus</td>
			<td>MIR2300</td>
			<td>for lipofection only</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Opti-MEM</td>
			<td>ThermoFisher</td>
			<td>31985062</td>
			<td>for lipofection only</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">G418 (Neomycin)</td>
			<td>Sigma Aldrich</td>
			<td>A1720-5G</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Hygromycin</td>
			<td>Sigma Aldrich</td>
			<td>H3274-250MG</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">96 well plates</td>
			<td>ThermoFisher</td>
			<td>12556008</td>
			<td></td>
		</tr>
		<tr height="18">
			<td height="18" style="height:18px;">Passive Lysis Buffer, 5x</td>
			<td>Promega</td>
			<td></td>
			<td></td>
		</tr>
		<tr height="18">
			<td height="18" style="height:18px;">1xSDS loading buffer</td>
			<td></td>
			<td></td>
			<td>recipe decribed in protocol</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Nitrocellulose Membrane</td>
			<td>Bio-Rad</td>
			<td>162-0115</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">TBST</td>
			<td></td>
			<td></td>
			<td>recipe decribed in protocol</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Dehydrated milk</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">SuperSignal West Dura Extended Duration Substrate</td>
			<td>ThermoFisher</td>
			<td>34075</td>
			<td>for HRP-conjugated secondary antibodies</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Extracta DNA prep for PCR</td>
			<td>Quantabio</td>
			<td>95091-025</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">KOD polymerase</td>
			<td>Novagen</td>
			<td>71316</td>
			<td></td>
		</tr>
	</tbody>
</table>

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.

For the generation of ELAVL1 knockout lines, a robust antibody was available, so editing using single sgRNAs (Figure 1A, left) was performed, followed by dot immunoblot. Three sgRNAs were transfected independently to compare efficiencies and to rule out off target effects in the resulting clones. After collecting and blotting cell lysates from clonal populations onto two nitrocellulose membranes, the blots were probed for both ELAVL1 and PUM2 (as a normalizat...

Watch this Scientific Journal Video about Selection-dependent and Independent Generation of CRISPR/Cas9-mediated Gene Knockouts in Mammalian Cells at JoVE.com

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

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 ...

The goal of this procedure is to isolate and identify clonal knockout cell lines generated by two types of CRIPSR/Cas9-mediated genome editing. One method detects protein knockout caused by nonhomologous end joining while the other detects genomic perturbations generated by homology-directed repair. This method is particularly useful in the field of molecular biology, where generation of cell lines with genetic perturbations is an important tool in dissecting gene function.The main advantage of this technique is that it is a quick and relatively high-throughput method that can be easily executed using basic molecular biology techniques. Nonhomologous end joining introduces small deletions or insertions, and are assessed by a dot immunoblot, while homology-directed repair allows for larger and more precise perturbations, and are assessed by colony PCR. This experiment uses T-REx-293 cells cultured in DMEM media, supplemented with 10%FBS at 37 degrees Celsius, and 5%carbon dioxide.Prior to transvection, plate the cells onto six well plates and include a well for an untransvected control. Grow the cells to approximately 70%confluency. Transvect the cells with 2.5 micrograms of total plasmid using a commercial transvection protocol.For transvection of cells without selection, use 2.5 micrograms of Cas9-sgRNA plasmid. For transvection of cells with selection, use 0.75 micrograms of Cas9-sgRNA1, 0.75 micrograms of Cas9-sgRNA2, and one microgram of homologous recombination template. Incubate the transvected cells and the untransvected control at 37 degrees Celsius and 5%carbon dioxide for 48 hours.For cells transvected with selection, begin the drug selection by treating the cells with the appropriate drug, which is Neomycin in this case. Return the six-well plate to the incubator. Observe the treated cells once a day to check for rates of cell death, until all cells in the untransvected control die.To isolate clonal populations, first grow the cells to 100%confluency in the original well after selection. Next make serial dilutions of the cells and count the cells. Since the proper generation of monoclonal colonies is key to obtaining a full knockout, care must be taken to determine the correct dilution for seating cells at the desired density.Once the correct dilution has been determined, seat the cells into 96-well plates at a density of 0.33 cells per well. Seating three 96=well plates is a good starting point to ensure isolation of more than one correct clone. Over a two-to-four week period, observe the colonies until colonies are visible to the eye.These representative images show colonies at different stages of growth. A single cell at seating, cells at day five, and a well-established colony at day 10. Using a sterile pipette tip, pick visible colonies with care and precision, and reseat in new wells to encourage monolayer growth.Continue growing the cells at 37 degrees Celsius and 5%carbon dioxide. Knockout candidates without selection are screened by dot immunoblot to assess the protein product in a high-throughput manner. After growing individual clones to 50 to 100%confluency, dislodge the monolayer of cells by pipetting within the well.Aliquot 90 microliters of the 100 microliter total volume from each well to a clean microcentrifuge tube. For the purposes of this video, only two samples will be processed. Spin down at 6, 000 RPM for five minutes, remove the media, and lyse the cell pallet in 10 microliters of 1X SDS loading buffer.Add 90 microliters of new media to the remainder of the cells in the well, and return the plate to the incubator to continue propagating the cells. Pipette one microliter of cell lysate onto a dry nitrocellulose membrane to form a dot. Blot each sample twice on two separate membranes, creating two identical patterns of samples.Block the membranes in 5%milk in TBST at room temperature, with rocking, for one hour. After one hour, blot the membranes with primary antibodies at the recommended primary antibody dilution, and TBST plus 5%milk. On one membrane use the primary antibody against the target protein, ELAVL1 in this experiment.On the other membrane, use the primary antibody for a control protein that is not expected to change, PUM2 is used here. Incubate at room temperature for one hour. Remove the primary antibody solution from each blot, add TBST, and incubate for five minutes.In this manner, wash the blots three times with TBST. Next, add to each membrane the appropriate HRP conjugated secondary antibody, and blot at room temperature for one hour. After one hour, wash the membranes three times with TBST for five minutes each time.Apply a chemiluminescent substrate solution to the blots, following the manufacturer's instructions, and image the blotted membranes on a digital chemiluminescence imager. Lastly, quantify dot intensities for the target and control proteins using the appropriate software, and analyze the results as described in the text protocol. Candidates with the selectable resistance marker are screened by colony PCR.Begin this procedure by duplicating individual colonies in a new 96-well plate, and growing them to 100%confluency for preparation of cell lysates. Remove the media from one set of the clones, resuspend the cells from each well in 30 microliters of extraction buffer from a commercial DNA preparation kit, and transfer to a clean 1.5 milliliter microcentrifuge tube. Heat the solution to 96 degrees Celsius for 15 minutes, and then let cool to room temperature.Add 30 microliters of stabilization buffer to each microcentrifuge tube and mix well. To identify wild-type and monoallelic or biallelic mutant lines by colony PCR, design two separate sets of PCR primers to amplify regions around the homology arms based on either successful or unsuccessful integration of the resistance cassette. On each side, use a common primer that anneals outside of the homology arm.To test for the wild-type allele, use the common primer with the corresponding paired primer that is complementary to the endogenous sequence spanning the homology region. To test for the desired mutation, use the common primer with another paired primer, complementary to the inserted resistance cassette. For each sample to be tested, prepare a reaction mixture containing the following, 0.5 microliters of cell lysate, 1.25 microliters of 10X KOD buffer, 0.75 microliters of 25 millimolar magnesium sulfate, 1.25 microliters of two millimolar dNTPs, 0.375 microliters of forward primer, 0.375 microliters of reverse primer, 0.25 microliters of KOD polymerase, and 7.75 microliters of water.Perform PCR using the following conditions, 95 degrees Celsius for two minutes, followed by 25 cycles of 95 degree Celsius for 20 seconds, primer melting temperature for 10 seconds, and 70 degrees Celsius for 20 seconds per KB.Subsequently, visualize the PCR products by agarose gel electrophoresis. Genome editing using non-homologous end joining was performed to generate ELAVL1 knockout lines followed by dot immunoblot, probing for ELAVL1 and PUM2. Clones that displayed little control signal were marked with an X, and excluded from further analysis.Clones with low ELAVL1 signals were further tested by western blot. Confirmed candidates are indicated in green, and invalidated candidates are indicated in gray. This graphic shows the ratios of ELAVL1 to control protein signal in increasing order.In most cases, clonal populations with the lowest relative ELAVL1 signal were correctly identified as knockouts. Candidates generated by the homology directed repair method were screened by colony PCR, and the PCR products visualized by agarose gel electrophoresis. Shown are example results using primers spanning the upstream integration junction using endogenous inside primers and knockout inside primers.Primers were first validated in both parental cells and bulk selected cells. Results from 24 individual candidate clones are shown together with the expected band patters for wild-type, knockout, and monoallelic deletion clones. The black arrows indicate the correct amplification products, stars indicate biallelic knockout clones.The biallelic mutant lines were further validated by western blot. Nonhomologous end joining uses a single Cas9 cut and selection-independent screening, thus requiring little up-front preparation, and screening for knockout clones by dot blots can quickly determine if a knockout generation was successful. PCR-based screening accurately detects correct candidates with large genomic perturbations generated by homology-directed repair.These techniques enable researchers in molecular biology to easily and efficiently identify knockouts, allowing them to explore normal or dysfunctional cellular processes using cell lines. After watching this video, you should have a good understanding of how to isolate and identify clonal knockout cell lines generated by CRISPR/Cas9 mediated genome editing.

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Research

JoVE Journal

Genetics

Rearing and Double-stranded RNA-mediated Gene Knockdown in the Hide Beetle, Dermestes maculatus

Advances in genomics have raised the possibility of probing biodiversity at an unprecedented scale. However, sequence alone will not be informative without tools to study gene function. The development and sharing of detailed protocols for the establishment of new model systems in laboratories, and for tools to carry out functional studies, is thus crucial for leveraging the power of genomics. Coleoptera (beetles) are the largest clade of insects and occupy virtually all types of habitats on the planet. In addition to providing ideal models for fundamental research, studies of beetles can have impacts on pest control as they are often pests of households, agriculture, and food industries. Detailed protocols for rearing and maintenance of D. maculatus laboratory colonies and for carrying out dsRNA-mediated interference in D. maculatus are presented. Both embryonic and parental RNAi procedures-including apparatus set up, preparation, injection, and post-injection recovery-are described. Methods are also presented for analyzing embryonic phenotypes, including viability, patterning defects in hatched larvae, and cuticle preparations for unhatched larvae. These assays, together with in situ hybridization and immunostaining for molecular markers, make D. maculatus an accessible model system for basic and applied research. They further provide useful information for establishing procedures in other emerging insect model systems.

Rearing and Double-stranded RNA-mediated Gene Knockdown in the Hide Beetle, Dermestes maculatus

Here, we present protocols for rearing an intermediate-germ beetle, Dermestes maculatus (D. maculatus) in the lab. We also share protocols for embryonic and parental RNAi and methods for analyzing embryonic phenotypes to study gene function in this species.

Advances in genomics have raised the possibility of probing biodiversity at an unprecedented scale. However, sequence alone will not be informative ...

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 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 ...

A Standard Methodology to Examine On-site Mutagenicity As a Function of Point Mutation Repair Catalyzed by CRISPR/Cas9 and SsODN in Human Cells

Combinatorial gene editing using CRISPR/Cas9 and single-stranded oligonucleotides is an effective strategy for the correction of single-base point mutations, which often are responsible for a variety of human inherited disorders. Using a well-established cell-based model system, the point mutation of a single-copy mutant eGFP gene integrated into HCT116 cells has been repaired using this combinatorial approach. The analysis of corrected and uncorrected cells reveals both the precision of gene editing and the development of genetic lesions, when indels are created in uncorrected cells in the DNA sequence surrounding the target site. Here, the specific methodology used to analyze this combinatorial approach to the gene editing of a point mutation, coupled with a detailed experimental strategy to measuring indel formation at the target site, is outlined. This protocol outlines a foundational approach and workflow for investigations aimed at developing CRISPR/Cas9-based gene editing for human therapy. The conclusion of this work is that on-site mutagenesis takes place as a result of CRISPR/Cas9 activity during the process of point mutation repair. This work puts in place a standardized methodology to identify the degree of mutagenesis, which should be an important and critical aspect of any approach destined for clinical implementation.

This protocol outlines the workflow of a CRISPR/Cas9-based gene editing system for the repair of point mutations in mammalian cells. Here, we use a combinatorial approach to gene editing with a detailed follow-on experimental strategy for measuring indel formation at the target site&#8212;in essence, analyzing onsite mutagenesis.

Combinatorial gene editing using CRISPR/Cas9 and single-stranded oligonucleotides is an effective strategy for the correction of single-base point ...

Generation of a Gene-disrupted Streptococcus mutans Strain Without Gene Cloning

Typical methods for the elucidation of the function of a particular gene involve comparative phenotypic analyses of the wild-type strain and a strain in which the gene of interest has been disrupted. A gene-disruption DNA construct containing a suitable antibiotic resistance marker gene is useful for the generation of gene-disrupted strains in bacteria. However, conventional construction methods, which require gene cloning steps, involve complex and time-consuming protocols. Here, a relatively facile, rapid, and cost-effective method for targeted gene disruption in Streptococcus mutans is described. The method utilizes a 2-step fusion polymerase chain reaction (PCR) to generate the disruption construct and electroporation for genetic transformation. This method does not require an enzymatic reaction, other than PCR, and additionally offers greater flexibility in terms of the design of the disruption construct. Employment of electroporation facilitates the preparation of competent cells and improves the transformation efficiency. The present method may be adapted for the generation of gene-disrupted strains of various species.

Generation of a Gene-disrupted Streptococcus mutans Strain Without Gene Cloning

We describe a facile, rapid, and relatively inexpensive method for the generation of gene-disrupted Streptococcus mutans strains; this technique may be adapted for the generation of gene-disrupted strains of various species.

Typical methods for the elucidation of the function of a particular gene involve comparative phenotypic analyses of the wild-type strain and a strain in ...

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 ...

Efficient Production and Identification of CRISPR/Cas9-generated Gene Knockouts in the Model System Danio rerio

Characterization of the clustered, regularly interspaced, short, palindromic repeat (CRISPR) system of Streptococcus pyogenes has enabled the development of a customizable platform to rapidly generate gene modifications in a wide variety of organisms, including zebrafish. CRISPR-based genome editing uses a single guide RNA (sgRNA) to target a CRISPR-associated (Cas) endonuclease to a genomic DNA (gDNA) target of interest, where the Cas endonuclease generates a double-strand break (DSB). Repair of DSBs by error-prone mechanisms lead to insertions and/or deletions (indels). This can cause frameshift mutations that often introduce a premature stop codon within the coding sequence, thus creating a protein-null allele. CRISPR-based genome engineering requires only a few molecular components and is easily introduced into zebrafish embryos by microinjection. This protocol describes the methods used to generate CRISPR reagents for zebrafish microinjection and to identify fish exhibiting germline transmission of CRISPR-modified genes. These methods include in vitro transcription of sgRNAs, microinjection of CRISPR reagents, identification of indels induced at the target site using a PCR-based method called a heteroduplex mobility assay (HMA), and characterization of the indels using both a low throughput and a powerful next-generation sequencing (NGS)-based approach that can analyze multiple PCR products collected from heterozygous fish. This protocol is streamlined to minimize both the number of fish required and the types of equipment needed to perform the analyses. Furthermore, this protocol is designed to be amenable for use by laboratory personal of all levels of experience including undergraduates, enabling this powerful tool to be economically employed by any research group interested in performing CRISPR-based genomic modification in zebrafish.

Efficient Production and Identification of CRISPR/Cas9-generated Gene Knockouts in the Model System Danio rerio

Targeted genome editing in the model system Danio rerio (zebrafish) has been greatly facilitated by the emergence of CRISPR-based approaches. Herein, we describe a streamlined, robust protocol for generation and identification of CRISPR-derived nonsense alleles that incorporates the heteroduplex mobility assay and identification of mutations using next-generation sequencing.

Characterization of the clustered, regularly interspaced, short, palindromic repeat (CRISPR) system of Streptococcus pyogenes has enabled the development ...

Adaptation of Hybridization Capture of Chromatin-associated Proteins for Proteomics to Mammalian Cells

The hybridization capture of chromatin-associated proteins for proteomics (HyCCAPP) technology was initially developed to uncover novel DNA-protein interactions in yeast. It allows analysis of a target region of interest without the need for prior knowledge about likely proteins bound to the target region. This, in theory, allows HyCCAPP to be used to analyze any genomic region of interest, and it provides sufficient flexibility to work in different cell systems. This method is not meant to study binding sites of known transcription factors, a task better suited for Chromatin Immunoprecipitation (ChIP) and ChIP-like methods. The strength of HyCCAPP lies in its ability to explore DNA regions for which there is limited or no knowledge about the proteins bound to it. It can also be a convenient method to avoid biases (present in ChIP-like methods) introduced by protein-based chromatin enrichment using antibodies. Potentially, HyCCAPP can be a powerful tool to uncover truly novel DNA-protein interactions. To date, the technology has been predominantly applied to yeast cells or to high copy repeat sequences in mammalian cells. In order to become the powerful tool we envision, HyCCAPP approaches need to be optimized to efficiently capture single-copy loci in mammalian cells. Here, we present our adaptation of the initial yeast HyCCAPP capture protocol to human cell lines, and show that single-copy chromatin regions can be efficiently isolated with this modified protocol.

This is a method to identify novel DNA-interacting proteins at specific target loci, relying on sequence-specific capture of crosslinked chromatin for subsequent proteomic analyses. No prior knowledge about potential binding proteins, nor cell modifications are required. Initially developed for yeast, the technology has now been adapted for mammalian cells.

The hybridization capture of chromatin-associated proteins for proteomics (HyCCAPP) technology was initially developed to uncover novel DNA-protein ...

Formaldehyde-assisted Isolation of Regulatory Elements to Measure Chromatin Accessibility in Mammalian Cells

Appropriate gene expression in response to extracellular cues, that is, tissue- and lineage-specific gene transcription, critically depends on highly defined states of chromatin organization. The dynamic architecture of the nucleus is controlled by multiple mechanisms and shapes the transcriptional output programs. It is, therefore, important to determine locus-specific chromatin accessibility in a reliable fashion that is preferably independent from antibodies, which can be a potentially confounding source of experimental variability. Chromatin accessibility can be measured by various methods, including the Formaldehyde-Assisted Isolation of Regulatory Elements (FAIRE) assay, that allow the determination of general chromatin accessibility in a relatively low number of cells. Here we describe a FAIRE protocol that allows simple, reliable, and fast identification of genomic regions with a low protein occupancy. In this method, the DNA is covalently bound to the chromatin proteins using formaldehyde as a crosslinking agent and sheared to small pieces. The free DNA is afterwards enriched using phenol:chloroform extraction. The ratio of free DNA is determined by quantitative polymerase chain reaction (qPCR) or DNA sequencing (DNA-seq) compared to a control sample representing total DNA. The regions with a looser chromatin structure are enriched in the free DNA sample, thus allowing the identification of genomic regions with lower chromatin compaction.

The plasticity of nuclear architecture is controlled by dynamic epigenetic mechanisms including non-coding RNAs, DNA methylation, nucleosome repositioning as well as histone composition and modification. Here we describe a Formaldehyde-Assisted Isolation of Regulatory Elements (FAIRE) protocol which allows the determination of chromatin accessibility in a reproducible, inexpensive, and straightforward manner.

Appropriate gene expression in response to extracellular cues, that is, tissue- and lineage-specific gene transcription, critically depends on highly ...

Highly Efficient Gene Disruption of Murine and Human Hematopoietic Progenitor Cells by CRISPR/Cas9

Advances in the hematopoietic stem cell (HSCs) field have been aided by methods to genetically engineer primary progenitor cells as well as animal models. Complete gene ablation in HSCs required the generation of knockout mice from which HSCs could be isolated, and gene ablation in primary human HSCs was not possible. Viral transduction could be used for knock-down approaches, but these suffered from variable efficacy. In general, genetic manipulation of human and mouse hematopoietic cells was hampered by low efficiencies and extensive time and cost commitments. Recently, CRISPR/Cas9 has dramatically expanded the ability to engineer the DNA of mammalian cells. However, the application of CRISPR/Cas9 to hematopoietic cells has been challenging, mainly due to their low transfection efficiencies, the toxicity of plasmid-based approaches and the slow turnaround time of virus-based protocols.
A rapid method to perform CRISPR/Cas9-mediated gene editing in murine and human hematopoietic stem and progenitor cells with knockout efficiencies of up to 90% is provided in this article. This approach utilizes a ribonucleoprotein (RNP) delivery strategy with a streamlined three-day workflow. The use of Cas9-sgRNA RNP allows for a hit-and-run approach, introducing no exogenous DNA sequences in the genome of edited cells and reducing off-target effects. The RNP-based method is fast and straightforward: it does not require cloning of sgRNAs, virus preparation or specific sgRNA chemical modification. With this protocol, scientists should be able to successfully generate knockouts of a gene of interest in primary hematopoietic cells within a week, including downtimes for oligonucleotide synthesis. This approach will allow a much broader group of users to adapt this protocol for their needs.

A protocol for fast CRISPR/Cas9-mediated gene disruption in mouse and human primary hematopoietic cells is described in this article. Cas9-sgRNA ribonucleoproteins are introduced via electroporation with sgRNAs generated through in vitro transcription and commercial Cas9. High editing efficiencies are achieved with limited time and financial cost.

Advances in the hematopoietic stem cell (HSCs) field have been aided by methods to genetically engineer primary progenitor cells as well as animal models. ...