M.H.T. is supported by an Agency for Science Technology and Research&#8217;s Joint Council Office grant (1431AFG103), a National Medical Research Council grant (OFIRG/0017/2016), National Research Foundation grants (NRF2013-THE001-046 and NRF2013-THE001-093), a Ministry of Education Tier 1 grant (RG50/17 (S)), a startup grant from Nanyang Technological University, and funds for the International Genetically Engineering Machine (iGEM) competition from Nanyang Technological University.

1. Design of sgRNAs
<ol>
	<li>Select an appropriate CRISPR-Cas system.
	<ol>
		<li>First, inspect the target region for the PAM sequences of all Cas9 and Cas12a nucleases that have been shown to be functional in mammalian cells16,21-32. Five frequently used enzymes are given in Table 1 together with their respective PAMs. 
		NOTE: Besides the endonucleases listed in Table 1, there are other less commonly used Cas enzymes that have been successfully deployed in mammalian...

The CRISPR-Cas system is a powerful, revolutionary technology to engineer the genomes and transcriptomes of plants and animals. Numerous bacterial species have been found to contain CRISPR-Cas systems, which may potentially be adapted for genome and transcriptome engineering purposes44. Although the Cas9 endonuclease from Streptococcus pyogenes (SpCas9) was the first enzyme to be deployed successfully in human cells21,22,</su...

The ability to engineer the genome of any living organism has many biomedical and biotechnological applications, such as the correction of disease-causing mutations, construction of accurate cellular models for disease studies, or generation of agricultural crops with desirable traits. Since the turn of the century, various technologies have been developed for genome engineering in mammalian cells, including meganucleases1,2,3, zinc finger nucleases4,5, or transcription activator-like effector nucleases (TALENs)6,7,8,9. However, these earlier technologies are either difficult to program or tedious to assemble, thereby hampering their widespread adoption in research and the industry.
In recent years, the clustered regularly interspaced short palindromic repeats (CRISPR)- CRISPR-associated (Cas) system has emerged as a powerful new genome engineering technology10,11. Originally an adaptive immune system in bacteria, it has been successfully deployed for genome modification in plants and animals, including humans. A primary reason why CRISPR-Cas has gained so much popularity in such a short time is that the element that brings the key Cas endonuclease, such as Cas9 or Cas12a (also known as Cpf1), to the correct location in the genome is simply a short piece of chimeric single guide RNA (sgRNA), which is straightforward to design and cheap to synthesize. After being recruited to the target site, the Cas enzyme functions as a pair of molecular scissors and cleaves the bound DNA with its RuvC, HNH, or Nuc domains12,13,14. The resulting double stranded break (DSB) is subsequently repaired by the cells via either the non-homologous end joining (NHEJ) or homology-directed repair (HDR) pathway. In the absence of a repair template, the DSB is repaired by the error-prone NHEJ pathway, which can give rise to pseudo-random insertion or deletion of nucleotides (indels) at the cut site, potentially causing frameshift mutations in protein-coding genes. However, in the presence of a donor template that contains the desired DNA changes, the DSB is repaired by the high fidelity HDR pathway. Common types of donor templates include single-stranded oligonucleotides (ssODNs) and plasmids. The former is typically used if the intended DNA changes are small (for example, alteration of a single base pair), while the latter is typically used if one wishes to insert a relatively long sequence (for example, the coding sequence of a green fluorescent protein or GFP) into the target locus.
The endonuclease activity of the Cas protein requires the presence of a protospacer adjacent motif (PAM) at the target site15. The PAM of Cas9 is at the 3&#8217; end of the protospacer, while the PAM of Cas12a (also called Cpf1) is at the 5&#8217; end instead16. The Cas-guide RNA complex is unable to introduce a DSB if the PAM is absent17. Hence, the PAM places a constraint on the genomic locations where a particular Cas nuclease is able to cleave. Fortunately, Cas nucleases from different bacterial species typically exhibit different PAM requirements. Hence, by integrating various CRISPR-Cas systems into our engineering toolbox, we can expand the range of sites that may be targeted in a genome. Moreover, a natural Cas enzyme can be engineered or evolved to recognize alternative PAM sequences, further widening the scope of genomic targets accessible to manipulation18,19,20.
Although multiple CRISPR-Cas systems are available for genome engineering purposes, most users of the technology have relied mainly on the Cas9 nuclease from Streptococcus pyogenes (SpCas9) for multiple reasons. First, it requires a relatively simply NGG PAM, unlike many other Cas proteins that can only cleave in the presence of more complex PAMs. Second, it is the first Cas endonuclease to be successfully deployed in human cells21,22,23,24. Third, SpCas9 is by far the best characterized enzyme to date. If a researcher wishes to use another Cas nuclease, he or she would often be unclear about how best to design the experiment and how well other enzymes will perform in different biological contexts compared to SpCas9.
To provide clarity to the relative performance of different CRISPR-Cas systems, we have recently performed a systematic comparison of five Cas endonucleases &#8211; SpCas9, the Cas9 enzyme from Staphylococcus aureus (SaCas9), the Cas9 enzyme from Neisseria meningitidis (NmCas9), the Cas12a enzyme from Acidaminococcus sp. BV3L6 (AsCas12a), and the Cas12a enzyme from Lachnospiraceae bacterium ND2006 (LbCas12a)25. For a fair comparison, we evaluated the various Cas nucleases using the same set of target sites and other experimental conditions. The study also delineated design parameters for each CRISPR-Cas system, which would serve as a useful reference for users of the technology. Here, to better enable researchers to make use of the CRISPR-Cas system, we provide a step-by-step protocol for optimal genome engineering with different Cas9 and Cas12a enzymes (see Figure 1). The protocol not only includes experimental details but also important design considerations to maximize the likelihood of a successful genome engineering outcome in mammalian cells.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/59086/59086fig1.jpg" /> 
Figure 1: An overview of the workflow to generate genome edited human cell lines. <a href="https://www.jove.com/files/ftp_upload/59086/59086fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

<table border="0" cellpadding="0" cellspacing="0" style="width:1424px;" width="1424">
	<colgroup>
		<col />
		<col />
		<col />
		<col />
	</colgroup>
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:443px;">T4 Polynucleotide Kinase (PNK)</td>
			<td style="width:175px;">NEB</td>
			<td style="width:119px;">M0201</td>
			<td style="width:688px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:443px;">Shrimp Alkaline Phosphatase (rSAP)</td>
			<td>NEB</td>
			<td style="width:119px;">M0371</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:443px;">Tris-Acetate-EDTA (TAE) Buffer, 50X</td>
			<td>1st Base</td>
			<td>BUF-3000-50X4L</td>
			<td>Dilute to 1X before use. The 1X solution contains 40 mM Tris, 20 mM acetic acid, and 1 mM EDTA.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:443px;">Tris-EDTA (TE) Buffer, 10X</td>
			<td>1st Base</td>
			<td>BUF-3020-10X4L</td>
			<td>Dilute to 1X before use. The 1X solution contains 10 mM Tris (pH 8.0) and 1 mM EDTA.&#160;</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:443px;">BbsI</td>
			<td>NEB</td>
			<td>R0539</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:443px;">BsmBI</td>
			<td>NEB</td>
			<td>R0580</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:443px;">T4 DNA Ligase</td>
			<td>NEB</td>
			<td style="width:119px;">M0202</td>
			<td>400,000 units/ml</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:443px;">Quick Ligation Kit</td>
			<td>NEB</td>
			<td style="width:119px;">M2200</td>
			<td>An alternative to T4 DNA Ligase.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:443px;">Rapid DNA Ligation Kit</td>
			<td>Thermo Scientific</td>
			<td style="width:119px;">K1423</td>
			<td>An alternative to T4 DNA Ligase.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:443px;">Zero Blunt TOPO PCR Cloning Kit</td>
			<td>Thermo Scientific</td>
			<td style="width:119px;">451245</td>
			<td>The salt solution comes with the TOPO vector in the kit.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:443px;">NEBuilder HiFi DNA Assembly Master Mix</td>
			<td>NEB</td>
			<td style="width:119px;">E2621L</td>
			<td>Kit for Gibson assembly.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:443px;">One Shot Stbl3 Chemically Competent E.Coli</td>
			<td>Thermo Scientific</td>
			<td style="width:119px;">C737303</td>
			<td></td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;width:443px;">LB Broth (Lennox), powder</td>
			<td>Sigma Aldrich</td>
			<td style="width:119px;">L3022</td>
			<td>Reconstitute in ddH20, and autoclave before use</td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;width:443px;">LB Broth with Agar (Lennox), powder</td>
			<td>Sigma Aldrich</td>
			<td style="width:119px;">L2897</td>
			<td>Reconstitute in ddH20, and autoclave before use</td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;width:443px;">SOC media</td>
			<td>-</td>
			<td style="width:119px;">-</td>
			<td>2.5 mM KCl, 10 mM MgCl2, 20 mM glucose in 1 L of LB Broth</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:443px;">Ampicillin (Sodium), USP Grade</td>
			<td>Gold Biotechnology</td>
			<td style="width:119px;">A-301</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:443px;">REDiant 2X PCR Mastermix</td>
			<td>1st Base</td>
			<td style="width:119px;">BIO-5185</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:443px;">Agarose</td>
			<td>1st Base</td>
			<td style="width:119px;">BIO-1000</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:443px;">T7 Endonuclease I</td>
			<td>NEB</td>
			<td style="width:119px;">M0302</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:443px;">Plasmid DNA Extraction Miniprep Kit</td>
			<td>Favorgen</td>
			<td style="width:119px;">FAPDE 300</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:443px;">Dulbecco&#39;s Modified Eagle Medium (DMEM), High Glucose</td>
			<td>Hyclone</td>
			<td>SH30081.01</td>
			<td>4.5 g/L Glucose, no L-glutamine, HEPES and Sodium Pyruvate</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:443px;">L-Glutamine, 200mM</td>
			<td>Gibco</td>
			<td style="width:119px;">25030</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:443px;">Penicillin-Streptomycin, 10, 000U/mL</td>
			<td>Gibco</td>
			<td style="width:119px;">15140</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:443px;">0.25% Trypsin-EDTA, 1X</td>
			<td>Gibco</td>
			<td style="width:119px;">25200</td>
			<td></td>
		</tr>
		<tr height="24">
			<td height="24" style="height:24px;width:443px;">Fetal Bovine Serum</td>
			<td>Hyclone</td>
			<td style="width:119px;">SV30160</td>
			<td>FBS is heat inactivated before use at 56 oC for 30 min</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:443px;">Phosphate Buffered Saline, 1X</td>
			<td>Gibco</td>
			<td style="width:119px;">20012</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:443px;">jetPRIME transfection reagent</td>
			<td>Polyplus Transfection</td>
			<td style="width:119px;">114-75</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:443px;">QuickExtract DNA Extraction Solution, 1.0</td>
			<td>Epicentre</td>
			<td style="width:119px;">LUCG-QE09050</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:443px;">ISOLATE II Genomic DNA Kit</td>
			<td>Bioline</td>
			<td style="width:119px;">BIO-52067</td>
			<td>An alternative to QuickExtract</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:443px;">Q5 High-Fidelity DNA Polymerase</td>
			<td>NEB</td>
			<td style="width:119px;">M0491</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:443px;">Deoxynucleotide (dNTP) Solution Mix</td>
			<td>NEB</td>
			<td style="width:119px;">N0447</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:443px;">6X DNA Loading Dye</td>
			<td>Thermo Scientific</td>
			<td>R0611</td>
			<td>10 mM Tris-HCl (pH 7.6) 0.03% bromophenol blue, 0.03% xylene cyanol FF, 60% glycerol, 60 mM EDTA</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:443px;">Protease Inhibitor Cocktail, Set3</td>
			<td>Merck</td>
			<td style="width:119px;">539134</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:443px;">Nitrocellulose membrane, 0.2&#181;m</td>
			<td>Bio-Rad</td>
			<td style="width:119px;">1620112</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:443px;">Tris-glycine-SDS buffer, 10X</td>
			<td>Bio-Rad</td>
			<td style="width:119px;">1610772</td>
			<td>Dilute to 1X before use. The 1x solution contains 25 mM Tris, 192 mM glycine, and 0.1% SDS.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:443px;">Tris-glycine buffer, 10X</td>
			<td>1st base</td>
			<td style="width:119px;">BUF-2020</td>
			<td>Dilute to 1X before use. The 1x solution contains 25 mM Tris and 192 mM glycine.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:443px;">Ponceau S solution</td>
			<td>Sigma Aldrich</td>
			<td style="width:119px;">P7170</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:443px;">TBS, 20X</td>
			<td>1st base</td>
			<td style="width:119px;">BUF-3030</td>
			<td>Dilute to 1X before use. The 1x solution contains 25 mM Tris-HCl (pH 7.5) and 150 mM NaCl.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:443px;">Tween 20</td>
			<td>Sigma Aldrich</td>
			<td style="width:119px;">P9416</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:443px;">Skim Milk for immunoassay</td>
			<td>Nacalai Tesque</td>
			<td style="width:119px;">31149-75</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:443px;">WesternBright Sirius-femtogram HRP</td>
			<td>Advansta</td>
			<td style="width:119px;">K12043</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:443px;">Antibody for &#946;-actin (C4)</td>
			<td>Santa Cruz Biotechnology</td>
			<td style="width:119px;">sc-47778</td>
			<td>Lot number: C0916</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:443px;">MiSeq system</td>
			<td>Illumina</td>
			<td style="width:119px;">SY-410-1003</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:443px;">NanoDrop spectrophotometer</td>
			<td>Thermo Scientific</td>
			<td style="width:119px;">ND-2000</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:443px;">Qubit fluorometer</td>
			<td>Thermo Scientific</td>
			<td style="width:119px;">Q33226</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:443px;">EVOS FL Cell Imaging System</td>
			<td>Thermo Scientific</td>
			<td style="width:119px;">AMF4300</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:443px;">CRISPR plasmid: pSpCas9(BB)-2A-GFP (PX458)</td>
			<td>Addgene</td>
			<td style="width:119px;">48138</td>
			<td>Single vector system: The gRNA is expressed from the same plasmid.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:443px;">CRISPR plasmid: pX601-AAV-CMV::NLS-SaCas9-NLS-3xHA-bGHpA</td>
			<td>Addgene</td>
			<td style="width:119px;">61591</td>
			<td>Single vector system: The gRNA is expressed from the same plasmid.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:443px;">CRISPR plasmid: xCas9 3.7</td>
			<td>Addgene</td>
			<td style="width:119px;">108379</td>
			<td>Dual vector system: The gRNA is expressed from a different plasmid.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:443px;">CRISPR plasmid: pX330-U6-Chimeric_BB-CBh-hSpCas9</td>
			<td>Addgene</td>
			<td style="width:119px;">42230</td>
			<td>Single vector system: The gRNA is expressed from the same plasmid.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:443px;">CRISPR plasmid: hCas9</td>
			<td>Addgene</td>
			<td style="width:119px;">41815</td>
			<td>Dual vector system: The gRNA is expressed from a different plasmid.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:443px;">CRISPR plasmid: eSpCas9(1.1)</td>
			<td>Addgene</td>
			<td style="width:119px;">71814</td>
			<td>Single vector system: The gRNA is expressed from the same plasmid.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:443px;">CRISPR plasmid: VP12 (SpCas9-HF1)</td>
			<td>Addgene</td>
			<td style="width:119px;">72247</td>
			<td>Dual vector system: The gRNA is expressed from a different plasmid.</td>
		</tr>
	</tbody>
</table>

genome editing in mammalian cell lines using crispr-cas

The clustered regularly interspaced short palindromic repeats (CRISPR) system functions naturally in bacterial adaptive immunity, but has been successfully repurposed for genome engineering in many different living organisms. Most commonly, the wildtype CRISPR associated 9 (Cas9) or Cas12a endonuclease is used to cleave specific sites in the genome, after which the DNA double-stranded break is repaired via the non-homologous end joining (NHEJ) pathway or the homology-directed repair (HDR) pathway depending on whether a donor template is absent or present respectively. To date, CRISPR systems from different bacterial species have been shown to be capable of performing genome editing in mammalian cells. However, despite the apparent simplicity of the technology, multiple design parameters need to be considered, which often leave users perplexed about how best to carry out their genome editing experiments. Here, we describe a complete workflow from experimental design to identification of cell clones that carry desired DNA modifications, with the goal of facilitating successful execution of genome editing experiments in mammalian cell lines. We highlight key considerations for users to take note of, including the choice of CRISPR system, the spacer length, and the design of a single-stranded oligodeoxynucleotide (ssODN) donor template. We envision that this workflow will be useful for gene knockout studies, disease modeling efforts, or the generation of reporter cell lines.

To perform a genome editing experiment, a CRISPR plasmid expressing a sgRNA targeting the locus-of-interest needs to be cloned. First, the plasmid is digested with a restriction enzyme (typically a type IIs enzyme) to linearize it. It is recommended to resolve the digested product on a 1% agarose gel alongside an undigested plasmid to distinguish between a complete and partial digestion. As undigested plasmids are supercoiled, they tend to run faster than their linearized counterparts (see Figure 7</...

Watch this Scientific Journal Video about Genome Editing in Mammalian Cell Lines using CRISPR-Cas at JoVE.com

Genome Editing in Mammalian Cell Lines using CRISPR-Cas

CRISPR-Cas is a powerful technology to engineer the complex genomes of plants and animals. Here, we detail a protocol to efficiently edit the human genome using different Cas endonucleases. We highlight important considerations and design parameters to optimize editing efficiency.

The clustered regularly interspaced short palindromic repeats (CRISPR) system functions naturally in bacterial adaptive immunity, but has been ...

This protocol uses CRISPR-Cas9 to create knock-out or knock-in lines. The main advantage of this technique is that it is simple and efficient to follow especially for novice researchers. For cell passaging, treat overnight cultured cells with two milliliters of 0.25%trypsin EDTA per plate at 37 degrees Celsius for two minutes.When the cells have lifted from the plate bottoms, neutralize the enzymatic reaction with two milliliters of cell culture medium, and transfer the cell suspension to a conical tube. Collect the cells by centrifugation and resuspend the pellet in five milliliters of fresh cell culture medium for counting. Then seed 1.8 times 10 to the fifth cells into one well of a 24-well tissue culture plate for overnight culture at 37 degrees Celsius and 5%carbon dioxide.For transfection of the cells, add an appropriate volume of transfection mix containing the appropriate concentration of CRISPR plasmid to the appropriate volume of transfection reagent, according to the experimental design and the manufacturer's instructions. After incubating the transfection mix at room temperature for the recommended period of time, add the solution to the cells in a drop-wise fashion. Then gently swirl the plate to mix and place the plate in a humidified 37 degree Celsius incubator with 5%carbon dioxide.At the end of the transfection, add 150 microliters of trypsin-EDTA to dissociate the cells as just demonstrated and collect the detached cells by centrifugation. Resuspend the pellet in 2%fetal bovine serum in PBS and filter the cells through a 30 micrometer mesh strainer into a five milliliter fluorescence-activated cell sorting, or FACS tube. Then use the non-transfected cells to set a negative control gate on the flow cytometer and sort the transfected cells according to the fluorescent marker on the CRISPR plasmid used for the transfection into a tube containing 100 microliters of cell culture medium.When all of the transfected cells have been collected, pellet the cells by centrifugation at maximum speed and resuspend the pellet in 300 microliters of cell culture medium. Seed 200 microliters of cells into one well of a 24-well tissue culture plate and allow the cells to recover for a few days in a 37 degree Celsius incubator. Pellet the remaining 100 microliters of sorted cells at maximum speed for five minutes and extract the genomic DNA from the resulting pellet according to standard DNA extraction protocols.Next, add 10 microliters of polymerase chain reaction buffer, one microliter of deoxynucleotide mix, 2.5 microliters of user-defined reverse primer, 0.5 microliters of DNA polymerase, two to five microliters of the extracted genomic DNA template and enough double-distilled water to bring the reaction to a final volume of 50 microliters. Run the mixture on a thermal cycler and resolve the reaction on a 2%agarose gel using 1X TAE buffer according to standard protocols. Use a clean, sharp scalpel to excise the polymerase chain react product and purify the DNA using a gel extraction kit according to the manufacturer's instructions.Measure the concentration of the product using a spectrophotometer at 260 nanometer absorbance. Prepare an assay mix containing 200 nanograms of the isolated DNA, two microliters of T7 endonuclease I reaction buffer, and enough double-distilled water to bring the final volume of the mixture to 19 microliters. Reanneal the polymerase chain reaction product in a thermal cycler at the indicated parameters and mix five units of T7 endonuclease I with the reannealed product for a 50 minute incubation at 37 degrees Celsius.At the end of the incubation, resolve the digested DNA on a 2.5%agarose gel using 1X TAE buffer, and image the gel on an appropriate gel imaging system. Open the gel image in ImageJ and draw a rectangular box around the band as close to its boundary as possible. Click Analyze, and Set Measurements, confirming that the area, mean gray value, and integrated density options are checked.Click OK, and select Analyze, and Measure. The mean, or raw intensity density value, is indicative of the band intensity. When the culture-transfected cells start becoming confluent, detach them with trypsin-EDTA, as demonstrated, and seed the cells sparsely in a 100 millimeter tissue culture dish to allow sufficient space for individual colonies to grow before returning the cells to the cell culture incubator.When the colonies begin to form, use a microscope with a four X magnification to pick the individual colonies for transfer into individual wells of a 24-well plate containing 500 microliters of cell culture medium per well. Take care that your tip does not touch the surrounding colonies to prevent mixing of colonies within individual wells or pick from an area of sparse colony growth. When all of the clones have been picked, place the plate in the cell culture incubator until the cultures become confluent.As undigested plasmids are super-coiled, they tend to run faster than their linearized counterparts. To determine if the oligonucleotides have been successfully cloned into the CRISPR plasmid backbone, colony PCR is performed and the positive clones are inoculated before the plasmids are extracted and sent for Sanger sequencing. The fluorescent signal can be readily visualized under a microscope upon a successful delivery of the plasmids, allowing the transfected cells to be sorted by flow cytometry.A T7 endonuclease I assay is performed to check the cleavage efficiency of the genomic DNA, as calculated from the intensities of the bands observed on an agarose gel. Additionally, if a homology-directed repair-based experiment is designed to incorporate a restriction site at the target locus, a restriction fragment length polymorphism assay can be performed with a corresponding restriction enzyme. To further validate that a protein coding gene has been successfully inactivated, a Western blot can be carried out to ensure that no targeted protein is present.Sorting the cells after transfection eliminates the cells without incorporated plasmids, thereby increasing the percentage of cells screened at later stages as having a knock-out or knock-in gene. With the development of this technique, we are now able to produce knock-out cell lines to study gene function and knock-in cell lines to model specific diseases to understand their mechanism.

genome-editing-in-mammalian-cell-lines-using-crispr-cas

Research

JoVE Journal

Genetics

20.7K visualizações.  Agency for Science Technology and Research. Este protocolo usa o CRISPR-Cas9 para criar linhas de knock-out ou knock-in. A principal vantagem dessa técnica é que ela é simples e eficiente de seguir especialmente para pesquisadores iniciantes. Para a passagem celular, trate células cultivadas durante a noite com dois mililitros de 0,25% de trippsina EDTA por placa a 37 graus Celsius por dois minutos.Quando as células tiverem levantado do fundo da placa, neutralizar a reação enzimática com dois mililitros de cultura celula...