This work was supported by a project grant from the Canadian Institute of Health Research (CIHR 365252), the Krembil Foundation and the Ontario Research Fund Research Excellence Round 8 (RE08-065). Sampath Kumar Loganathan is the recipient of a Canadian Cancer Society fellowship (BC-F-16#31919).

This protocol was approved and performed in accordance with IACUC of University of Toronto.
1. Design and cloning of pooled CRISPR libraries
<ol>
	<li>Select 4-5 sgRNAs targeting mouse genes of interest from resource such as the Broad Institute sgRNA designer (https://portals.broadinstitute.org/gpp/public/analysis-tools/sgrna-design) or CHOPCHOP server (https://chopchop.cbu.uib.no). Select an equal number of non-targeting sgRNAs from e.g., Sanjana et al.9 to generate ...

<ol>
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M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cutaneous+squamous+cell+carcinoma:+an+epidemiological+review.">Cutaneous squamous cell carcinoma: an epidemiological review.</a> British Journal of Dermatology. 177, 373-381 (2017).</li><li>Campbell, J. D., 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=pathway+network,+and+immunologic+features+distinguishing+squamous+carcinomas.">pathway network, and immunologic features distinguishing squamous carcinomas.</a> Cell Reports. 23, 194-212 (2018).</li><li>Sanjana, N. E., Shalem, O., Zhang, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Improved+vectors+and+genome-wide+libraries+for+CRISPR+screening.">Improved vectors and genome-wide libraries for CRISPR screening.</a> Nature Methods. 11, 783-784 (2014).</li><li>Geraerts, M., Willems, S., Baekelandt, V., Debyser, Z., Gijsbers, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Comparison+of+lentiviral+vector+titration+methods.">Comparison of lentiviral vector titration methods.</a> BMC Biotechnology. 6, 34 (2006).</li><li>Schramek, D., 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=Direct+in+vivo+RNAi+screen+unveils+myosin+IIa+as+a+tumor+suppressor+of+squamous+cell+carcinomas.">Direct in vivo RNAi screen unveils myosin IIa as a tumor suppressor of squamous cell carcinomas.</a> Science. 343, 309-313 (2014).</li><li>Platt, R. J., 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=CRISPR-Cas9+knockin+mice+for+genome+editing+and+cancer+modeling.">CRISPR-Cas9 knockin mice for genome editing and cancer modeling.</a> Cell. 159, 440-455 (2014).</li><li>Langmead, B., Trapnell, C., Pop, M., Salzberg, S. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ultrafast+and+memory-efficient+alignment+of+short+DNA+sequences+to+the+human+genome.">Ultrafast and memory-efficient alignment of short DNA sequences to the human genome.</a> Genome Biology. 10, 25 (2009).</li><li>Li, W., 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=MAGeCK+enables+robust+identification+of+essential+genes+from+genome-scale+CRISPR/Cas9+knockout+screens.">MAGeCK enables robust identification of essential genes from genome-scale CRISPR/Cas9 knockout screens.</a> Genome Biology. 15, 554 (2014).</li><li>Winters, I. P., Murray, C. W., Winslow, M. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Towards+quantitative+and+multiplexed+in+vivo+functional+cancer+genomics.">Towards quantitative and multiplexed in vivo functional cancer genomics.</a> Nature Reviews Genetics. 19, 741-755 (2018).</li><li>Rogers, Z. N., 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=Mapping+the+in+vivo+fitness+landscape+of+lung+adenocarcinoma+tumor+suppression+in+mice.">Mapping the in vivo fitness landscape of lung adenocarcinoma tumor suppression in mice.</a> Nature Genetics. 50, 483-486 (2018).</li><li>Chow, R. D., 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=AAV-mediated+direct+in+vivo+CRISPR+screen+identifies+functional+suppressors+in+glioblastoma.">AAV-mediated direct in vivo CRISPR screen identifies functional suppressors in glioblastoma.</a> Nature Neuroscience. 20, 1329-1341 (2017).</li><li>Wang, G., 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=Mapping+a+functional+cancer+genome+atlas+of+tumor+suppressors+in+mouse+liver+using+AAV-CRISPR&#8211;mediated+direct+in+vivo+screening.">Mapping a functional cancer genome atlas of tumor suppressors in mouse liver using AAV-CRISPR&#8211;mediated direct in vivo screening.</a> Science Advances. 4, 5508 (2018).</li><li>Chan, K., Tong, A. H. Y., Brown, K. R., Mero, P., Moffat, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Pooled+CRISPR-based+genetic+screens+in+mammalian+cells.">Pooled CRISPR-based genetic screens in mammalian cells.</a> Journal of Visualized Experiments. (151), e59780 (2019).</li><li>Hart, T., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=High-resolution+CRISPR+screens+reveal+fitness+genes+and+genotype-specific+cancer+liabilities.">High-resolution CRISPR screens reveal fitness genes and genotype-specific cancer liabilities.</a> Cell. 163, 1515-1526 (2015).</li></ol>

CRISPR/Cas9 genome editing has been widely used in in vitro and in vivo studies to investigate gene functions and cellular processes. Most in vivo studies utilize CRISPR/Cas9 gene edited cells grafted into an animal model (allograft or xenograft). While this is a powerful tool to study cancer genetics and cellular functions, it still lacks the native tissue microenvironment and might elicit wounding and/or immune responses.
To overcome these challenges, several groups have pioneered direct in ...

One of the challenges for cancer research in the post-genomic era is to mine the vast amount of genome data for causal gene mutations and to identify nodes in the gene network that can be targeted therapeutically. While bioinformatic analyses have helped immensely towards these goals, establishing efficient in vitro and in vivo models is a prerequisite to decipher the complexity of biological systems and disease states and for enabling drug development. While conventional transgenic mouse models have been used extensively for in vivo cancer genetics studies, their cost-, time- and labor-intensive nature has largely prohibited the systematic analysis of the hundreds of putative cancer genes unraveled by modern genomics. To overcome this bottleneck, we combined a previously established ultrasound-guided in utero injection methodology1,2 with a CRISPR/Cas9 (Clustered Regularly Interspaced Short Palindromic Repeats) gene editing technology3 to simultaneously induce and study loss-of-function mutations of hundreds of genes in skin and oral cavity of a single mouse.
The methodology described here utilizes ultrasound-guided injections of engineered lentiviruses into the amniotic cavity of living mouse embryos at embryonic day E9.5. The lentiviral cargo containing CRISPR/Cas9 components transduce the single-layered surface ectoderm, which later gives rise to the epithelium of the skin and oral cavity. Skin is composed of an outer epidermis, followed by basement membrane and dermis. Epidermis is a stratified epithelium composed of an inner, basal layer, which maintains contact with the basement membrane and has proliferative and stem cell capacity. The basal layer gives rise to the differentiated layers above such as spinous, granular and stratum corneum layers2,4. Lineage tracing studies show that this direct in vivo CRISPR/Cas9 method genetically manipulates tissue-resident stem cells within the basal layer that persist throughout adulthood. As lentivirus can be titrated to transduce the E9.5 surface ectoderm at clonal density, this method can be used to generate mosaic mice harboring thousands of discrete gene knock-out clones. Next generation sequencing can then be used to analyze the effect of CRISPR/Cas9-mediated gene ablation within those clones in a multiplexed manner5.
We recently used this method to assess the function of 484 genes that show recurrent mutations in human Head and Neck Squamous Cell Carcinoma (HNSCC)5. HNSCC is a devastating cancer with a high mortality rate of 40&#8211;50% and it is the 6th most common cancer worldwide6. HNSCC arise in mucosal linings of the upper airway or oral cavity and are associated with tobacco and alcohol consumption or human papillomavirus (HPV) infection. Cutaneous Squamous Cell Carcinoma (SCC) are skin tumors and represent the second most common cancer in humans7. Cutaneous SCC and HNSCC are histologically and molecularly very similar, with a high percentage of cases exhibiting alteration in TP53, PIK3CA, NOTCH1, and HRAS8. While there are only a handful of genes mutated at high frequency, there are hundreds of genes found mutated at low frequency (&#60; 5%), a phenomenon commonly referred to as the long-tail distribution. As the majority of the long-tail genes lack biological or clinical validation, we used this in vivo CRISPR screening technology to model loss-of-function of these genes in tumor-prone mice with sensitizing mutations in p53, Pik3ca or Hras and identified several novel tumor suppressor genes that cooperate with p53, Pik3ca or Hras to trigger tumor development5.
Here, we describe a detailed protocol to generate multiplexed sgRNA lentiviral CRISPR sgRNA libraries and perform CRISPR/Cas9 gene knock-out screens in the mouse surface ectoderm. Of note, this methodology can be adapted to incorporate other gene manipulation technologies such as CRISPR activation (CRISPRa) and CRISPR inactivation (CRISPRi) or modified to target other organ systems in mouse to study gene functions.

<table>
	<tbody>
		<tr>
			<td>0.45 micron filter</td>
			<td>Sigma</td>
			<td>S2HVU02RE</td>
			<td></td>
		</tr>
		<tr>
			<td>12k or 92k oligo chip</td>
			<td>Customarray Inc. (Genscript)</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>15 cm cell culture plates</td>
			<td>Corning</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>293FT</td>
			<td>Invitrogen</td>
			<td>R70007</td>
			<td></td>
		</tr>
		<tr>
			<td>293NT</td>
			<td>Systems Biosciences</td>
			<td>LV900A-1</td>
			<td></td>
		</tr>
		<tr>
			<td>Alkaline phosphatase</td>
			<td>NEB</td>
			<td>M0290L</td>
			<td></td>
		</tr>
		<tr>
			<td>Amplicillin</td>
			<td>Fisher Scientific</td>
			<td>BP1760-25</td>
			<td></td>
		</tr>
		<tr>
			<td>ATP</td>
			<td>NEB</td>
			<td>9804S</td>
			<td></td>
		</tr>
		<tr>
			<td>BsmBI</td>
			<td>NEB</td>
			<td>R0580L</td>
			<td></td>
		</tr>
		<tr>
			<td>Chromic gut suture</td>
			<td>Covidien</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Deep sequencing (Next-Seq or Hi-Seq)</td>
			<td>Illumina</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>DNA-cleanup kit</td>
			<td>Zymo Research</td>
			<td>D4008</td>
			<td></td>
		</tr>
		<tr>
			<td>DNAesy Blood and Tissue DNA extraction kit</td>
			<td>Qiagen</td>
			<td>69506</td>
			<td></td>
		</tr>
		<tr>
			<td>Endura electrocompetent cells</td>
			<td>Lucigen</td>
			<td>60242-1</td>
			<td></td>
		</tr>
		<tr>
			<td>Glass Capillaries</td>
			<td>Drummond</td>
			<td>3-000-203-G/X</td>
			<td></td>
		</tr>
		<tr>
			<td>HEK293T cells</td>
			<td>ATCC</td>
			<td>CRL-3216</td>
			<td></td>
		</tr>
		<tr>
			<td>High-Speed Centrifuge</td>
			<td>Beckman Coulter</td>
			<td>MLS-50</td>
			<td></td>
		</tr>
		<tr>
			<td>LB Agar</td>
			<td>Wisent Technologies</td>
			<td>800-011-LG</td>
			<td></td>
		</tr>
		<tr>
			<td>Micropipette puller</td>
			<td>Sutter Instrument</td>
			<td>P97</td>
			<td></td>
		</tr>
		<tr>
			<td>Mineral oil</td>
			<td>Sigma</td>
			<td>M5904</td>
			<td></td>
		</tr>
		<tr>
			<td>Mini-prep plasmid Kit</td>
			<td>Frogga Bio</td>
			<td>PDH300</td>
			<td></td>
		</tr>
		<tr>
			<td>Mouse oxygen anaesthesia system</td>
			<td>Visual Sonics</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Nanoject II micromanipulator</td>
			<td>Drummond</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>NEBuffer 3.1 (Buffer for BsmBI)</td>
			<td>NEB</td>
			<td>R0580L</td>
			<td></td>
		</tr>
		<tr>
			<td>Needle sharpener</td>
			<td>Sutter Instrument</td>
			<td>BV-10</td>
			<td></td>
		</tr>
		<tr>
			<td>Oligo cleanup kit</td>
			<td>Zymo research</td>
			<td>D4060</td>
			<td></td>
		</tr>
		<tr>
			<td>PAGE purified illumina sequencing primer</td>
			<td>IDT DNA</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>PEI (polyethyleneimine)</td>
			<td>Sigma</td>
			<td>408727-100ML</td>
			<td></td>
		</tr>
		<tr>
			<td>Permoplast modeling clay</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Petridish with central opening</td>
			<td>Visual Sonics</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>pMD2.G</td>
			<td>Addgene</td>
			<td>12259</td>
			<td></td>
		</tr>
		<tr>
			<td>psPAX2</td>
			<td>Addgene</td>
			<td>12260</td>
			<td></td>
		</tr>
		<tr>
			<td>Q5 Polymerase 2x Master mix</td>
			<td>NEB</td>
			<td>M0494L</td>
			<td></td>
		</tr>
		<tr>
			<td>Qubit Fluorometric Quantification</td>
			<td>Invitrogen</td>
			<td>Q33327</td>
			<td></td>
		</tr>
		<tr>
			<td>Semicircular Silicone plug</td>
			<td>Corning</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Silicone membrane</td>
			<td>Visual Sonics</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>T4 DNA ligase</td>
			<td>NEB</td>
			<td>M0202L</td>
			<td></td>
		</tr>
		<tr>
			<td>Ultra-centrifuge tubes</td>
			<td>Beckman Coulter</td>
			<td>344058</td>
			<td></td>
		</tr>
		<tr>
			<td>Vevo2000 ultrasound system</td>
			<td>Visual Sonics</td>
			<td></td>
			<td></td>
		</tr>
	</tbody>
</table>

in vivo crispr/cas9 screening to simultaneously evaluate gene function in mouse skin and oral cavity

Genetically modified mouse models (GEMM) have been instrumental in assessing gene function, modeling human diseases, and serving as preclinical model to assess therapeutic avenues. However, their time-, labor- and cost-intensive nature limits their utility for systematic analysis of gene function. Recent advances in genome-editing technologies overcome those limitations and allow for the rapid generation of specific gene perturbations directly within specific mouse organs in a multiplexed and rapid manner. Here, we describe a CRISPR/Cas9-based method (Clustered Regularly Interspaced Short Palindromic Repeats) to generate thousands of gene knock-out clones within the epithelium of the skin and oral cavity of mice, and provide a protocol detailing the steps necessary to perform a direct&#160;in vivo&#160;CRISPR&#160;screen for tumor suppressor genes. This approach can be applied to other organs or other CRISPR/Cas9 technologies such as CRISPR-activation or CRISPR-inactivation to study the biological function of genes during tissue homeostasis or in various disease settings.

Figure 1A shows the design of the oligonucleotides for multiplexing several custom CRISPR libraries in a cost-effective manner in a single 12k or 92k oligo chip. Once the sgRNAs (blue color coded) are selected, the oligonucleotides are designed with restriction sites (orange colored BsmBI) and library specific PCR primer pairs (green color coded). Several libraries can be designed by using unique combination of primer pairs for multiplexing in a single oligo chip. When PCR amplifying the lib...

Watch this Scientific Journal Video about In Vivo CRISPR/Cas9 Screening to Simultaneously Evaluate Gene Function in Mouse Skin and Oral Cavity at JoVE.com

In Vivo CRISPR/Cas9 Screening to Simultaneously Evaluate Gene Function in Mouse Skin and Oral Cavity

Here we describe a rapid and direct in vivo CRISPR/Cas9 screening methodology using ultrasound-guided in utero embryonic lentiviral injections to simultaneously assess functions of several genes in the skin and oral cavity of immunocompetent mice.

Genetically modified mouse models (GEMM) have been instrumental in assessing gene function, modeling human diseases, and serving as preclinical model to ...

This protocol is significant because it allows researchers to simultaneously probe the tumor suppressive functions of hundreds of genes in head and neck cancer at a fraction of the cost of a conventional knockout mouse model. This technique is flexible and can be adapted to cover expression of genes to study their function in skin. The targeted CRISPR library protocol can also be applied for other cancer types.Place the anesthetized animal ventral side up on the heated surgery stage and use surgical tape to hold the paws in place. Apply the nosecone anesthesia tube for a constant supply of isoflurane and oxygen until the surgery is completed. To confirm E9.5 pregnancy, apply a small quantity of hair removal cream to the abdomen and to spread it over a three-by-three centimeter squared area using a cotton tipped applicator.After two to three minutes, gently remove the cream with gauze or tissue and wipe the area clean using PBS and 70%ethanol. Using the ultrasound probe and gel, check the pregnant mouse for embryonic day E9.5. This can also be done the day before at E8.5 to save time on the day of surgery.Remove the ultrasound gel and wipe the area clean using BPS and then 70%ethanol. Inject the most with subcutaneous analgesic. Then you sterile forceps and scissors to make a vertical incision in the skin.Use blunt forceps to separate the skin around the incision from the peritoneum. Then you sterile forceps and scissors to cut through the peritoneum. Using blunt forceps, gently pull out the left and right uterus horn and count the embryos.Reinsert most of the uterine horns, but leave the distal end of one uterine horn containing three embryos exposed. Using blunt forceps, gently push and pull the uterus with the three embryos, through the opening in the silicone membrane of the modified Petri dish. Stabilize the Petri dish using cubes of modeling clay.Stabilize the uterus with the three embryos inside the Petri dish, using a silicone mold. Then flatten the silicone plug at the side of the embryos using a blunt tool. Fill the Petri dish with sterile PBS and flush the silicone membrane on the bottom of the Petri dish, with the pregnant dam's belly, thereby preventing any leakage.Move the ultrasound head into the Petri dish, approximately 0.5 centimeters above the top embryo and adjust the stage so that the amniotic cavity becomes clearly visible in the ultrasound view. Align the injector needle, carefully into the modified Petri dish. Using the micromanipulator, place the tip of the needle within five millimeters of the top embryo, then toggle the needle back and forth to move into the plane where its tip appears the brightest in the ultrasound image.Using the micromanipulator, push the needle through the uterine wall into the amniotic cavity. Inject 62 nanoliters of the lentivirus with the sgRNA library at a slow injection speed. Press the Inject button eight times for a total of 496 nanoliters per embryo.Repeat the same procedure for the other two embryos. Then lift the ultrasound head and remove the silicone plug. Gently pushed the first two of the three embryos into the mouse abdomen using a sterile cotton swab.Pull out the next three embryos and push in the previously injected third embryo. Repeat the injection procedure until the desired number of embryos are injected, making sure to not exceed 30 minutes of anesthesia. When finished, lift the ultrasound head, remove the micromanipulator with the needle, aspirate the PBS and remove the Petri dish.Using sterile wipes, absorb any PBS that might have accumulated in the abdominal cavity. Close the peritoneal incision using absorbable sutures. Then use two staples to close the incision in the abdominal skin.Next, generation sequencing reads of PCR amplified DNA from plasmid and lentiviral library transduced cells should show a high correlation. If the sgRNA reads from plasmid DNA do not show equal representation of sgRNAs, then the viral preparation and concentration procedure must be repeated with care. The results of the ultrasound-guided injection of lentivirus carrying Cre recombinase in E9.5 Lox-STOP-Lox confetti mouse pups at postnatal day P0, are shown here.While high titer of virus would result in larger coverage of the mouse's skin, it would also result in transduction of multiple sgRNAs into the same cell. This plot shows next-generation sequencing reads of PCR-amplified DNA, from plasmid and lentiviral library transduced cells, as well as reads from four representative tumors. sgRNA guides targeting tumor suppressors ADAM10 and RIPK4 are enriched in the tumor samples compared to the plasmid pool or infected cells.Performing the surgery at E9.5 is critical. Remember to check for pregnancy with ultrasound, nine days after setting up the cross and identify the embryonic time point in each female mouse. Once the pups are born, the transduced cells can be isolated and extensively profiled using the latest gene profiling techniques such as single-cell RNA sequencing.

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Genetics

QTL Mapping and CRISPR/Cas9 Editing to Identify a Drug Resistance Gene in Toxoplasma gondii

Scientific knowledge is intrinsically linked to available technologies and methods. This article will present two methods that allowed for the identification and verification of a drug resistance gene in the Apicomplexan parasite Toxoplasma gondii, the method of Quantitative Trait Locus (QTL) mapping using a Whole Genome Sequence (WGS) -based genetic map and the method of Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)/Cas9 -based gene editing. The approach of QTL mapping allows one to test if there is a correlation between a genomic region(s) and a phenotype. Two datasets are required to run a QTL scan, a genetic map based on the progeny of a recombinant cross and a quantifiable phenotype assessed in each of the progeny of that cross. These datasets are then formatted to be compatible with R/qtl software that generates a QTL scan to identify significant loci correlated with the phenotype. Although this can greatly narrow the search window of possible candidates, QTLs span regions containing a number of genes from which the causal gene needs to be identified. Having WGS of the progeny was critical to identify the causal drug resistance mutation at the gene level. Once identified, the candidate mutation can be verified by genetic manipulation of drug sensitive parasites. The most facile and efficient method to genetically modify T. gondii is the CRISPR/Cas9 system. This system comprised of just 2 components both encoded on a single plasmid, a single guide RNA (gRNA) containing a 20 bp sequence complementary to the genomic target and the Cas9 endonuclease that generates a double-strand DNA break (DSB) at the target, repair of which allows for insertion or deletion of sequences around the break site. This article provides detailed protocols to use CRISPR/Cas9 based genome editing tools to verify the gene responsible for sinefungin resistance and to construct transgenic parasites.

QTL Mapping and CRISPR/Cas9 Editing to Identify a Drug Resistance Gene in Toxoplasma gondii

Details are presented on how QTL mapping with a whole genome sequence based genetic map can be used to identify a drug resistance gene in Toxoplasma gondii and how this can be verified with the CRISPR/Cas9 system that efficiently edits a genomic target, in this case the drug resistance gene.

Scientific knowledge is intrinsically linked to available technologies and methods. This article will present two methods that allowed for 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 ...

Primordial Germ Cell Transplantation for CRISPR/Cas9-based Leapfrogging in Xenopus

The creation of mutant lines by genome editing is accelerating genetic analysis in many organisms. CRISPR/Cas9 methods have been adapted for use in the African clawed frog, Xenopus, a longstanding model organism for biomedical research. Traditional breeding schemes for creating homozygous mutant lines with CRISPR/Cas9-targeted mutagenesis have several time-consuming and laborious steps. To facilitate the creation of mutant embryos, particularly to overcome the obstacles associated with knocking out genes that are essential for embryogenesis, a new method called leapfrogging was developed. This technique leverages the robustness of Xenopus embryos to &#34;cut and paste&#34; embryological methods. Leapfrogging utilizes the transfer of primordial germ cells (PGCs) from efficiently-mutagenized donor embryos into PGC-ablated wildtype siblings. This method allows for the efficient mutation of essential genes by creating chimeric animals with wildtype somatic cells that carry a mutant germline. When two F0 animals carrying &#34;leapfrog transplants&#34; (i.e., mutant germ cells) are intercrossed, they produce homozygous, or compound heterozygous, null F1 embryos, thus saving a full generation time to obtain phenotypic data. Leapfrogging also provides a new approach for analyzing maternal effect genes, which are refractory to F0 phenotypic analysis following CRISPR/Cas9 mutagenesis. This manuscript details the method of leapfrogging, with special emphasis on how to successfully perform PGC transplantation.

Primordial Germ Cell Transplantation for CRISPR/Cas9-based Leapfrogging in Xenopus

Genes essential for survival pose technical hurdles for creating mutant lines. Leapfrogging circumvents lethality by combining genome editing with primordial germ cell transplantation to create wild-type animals carrying germline mutations. Leapfrogging also permits the efficient generation of homozygous null mutants in the F1 generation. Here, the transplantation step is demonstrated.

The creation of mutant lines by genome editing is accelerating genetic analysis in many organisms. CRISPR/Cas9 methods have been adapted for use in the ...

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 ...

Microinjection of CRISPR/Cas9 Protein into Channel Catfish, Ictalurus punctatus, Embryos for Gene Editing

The complete genome of the channel catfish, Ictalurus punctatus, has been sequenced, leading to greater opportunities for studying channel catfish gene function. Gene knockout has been used to study these gene functions in vivo. The clustered regularly interspaced short palindromic repeats/CRISPR associated protein 9 (CRISPR/Cas9) system is a powerful tool used to edit genomic DNA sequences to alter gene function. While the traditional approach has been to introduce CRISPR/Cas9 mRNA into the single cell embryos through microinjection, this can be a slow and inefficient process in catfish. Here, a detailed protocol for microinjection of channel catfish embryos with CRISPR/Cas9 protein is described. Briefly, eggs and sperm were collected and then artificial fertilization performed. Fertilized eggs were transferred to a Petri dish containing Holtfreter's solution. Injection volume was calibrated and then guide RNAs/Cas9 targeting the toll/interleukin 1 receptor domain-containing adapter molecule (TICAM 1) gene and rhamnose binding lectin (RBL) gene were microinjected into the yolk of one-cell embryos. The gene knockout was successful as indels were confirmed by DNA sequencing. The predicted protein sequence alterations due to these mutations included frameshift and truncated protein due to premature stop codons.

Microinjection of CRISPR/Cas9 Protein into Channel Catfish, Ictalurus punctatus, Embryos for Gene Editing

A simple and efficient microinjection protocol for gene editing in channel catfish embryos using the CRISPR/Cas9 system is presented. In this protocol, guide RNAs and Cas9 protein were microinjected into the yolk of one-cell embryos. This protocol has been validated by knocking out two channel catfish immune-related genes.

The complete genome of the channel catfish, Ictalurus punctatus, has been sequenced, leading to greater opportunities for studying channel catfish gene ...

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 ...

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. ...

CRISPR/Cas9 Gene Editing to Make Conditional Mutants of Human Malaria Parasite P. falciparum

Malaria is a significant cause of morbidity and mortality worldwide. This disease, which primarily affects those living in tropical and subtropical regions, is caused by infection with Plasmodium parasites. The development of more effective drugs to combat malaria can be accelerated by improving our understanding of the biology of this complex parasite. Genetic manipulation of these parasites is key to understanding their biology; however, historically the genome of P. falciparum has been difficult to manipulate. Recently, CRISPR/Cas9 genome editing has been utilized in malaria parasites, allowing for easier protein tagging, generation of conditional protein knockdowns, and deletion of genes. CRISPR/Cas9 genome editing has proven to be a powerful tool for advancing the field of malaria research. Here, we describe a CRISPR/Cas9 method for generating glmS-based conditional knockdown mutants in P. falciparum. This method is highly adaptable to other types of genetic manipulations, including protein tagging and gene knockouts.

CRISPR/Cas9 Gene Editing to Make Conditional Mutants of Human Malaria Parasite P. falciparum

We describe a method for generating glmS-based conditional knockdown mutants in Plasmodium falciparum using CRISPR/Cas9 genome editing.

Malaria is a significant cause of morbidity and mortality worldwide. This disease, which primarily affects those living in tropical and subtropical ...