Name: crispr/cas9 gene editing to make conditional mutants of human malaria parasite p. falciparum
Uploaded: 2018-09-18T12:30:00
Description: Watch this Scientific Journal Video about CRISPR/Cas9 Gene Editing to Make Conditional Mutants of Human Malaria Parasite P. falciparum at JoVE.com

We thank Muthugapatti Kandasamy at the University of Georgia (UGA) Biomedical Microscopy Core for technical assistance and Jose-Juan Lopez-Rubio for sharing the pUF1-Cas9 and pL6 plasmids. This work was supported by ARCS Foundation awards to D.W.C. and to H.M.K., UGA startup funds to V.M., grants from the March of Dimes Foundation (Basil O&#39;Connor Starter Scholar Research Award) to V.M., and US National Institutes of Health grants (R00AI099156 and R01AI130139) to V.M. and (T32AI060546) to H.M.K.

Continuous culture of P. falciparum requires the use of human RBCs, and we utilized commercially purchased units of blood that were stripped of all identifiers and anonymized. The Institutional Review Board and the Office of Biosafety at the University of Georgia reviewed our protocols and approved all protocols used in our lab.
1. Choosing a gRNA Sequence
<ol>
	<li>Go to CHOPCHOP (http://chopchop.cbu.uib.no/) and select &#39;Fasta Target&#39;. Under &#39;Target&#39;</e...

<ol>
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S. <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+in+Genome+Editing+and+Beyond.">CRISPR/Cas9 in Genome Editing and Beyond.</a> Annual Review of Biochemistry. 85, 227-264 (2016).</li><li>Kirkman, L. A., Deitsch, K. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Antigenic+variation+and+the+generation+of+diversity+in+malaria+parasites.">Antigenic variation and the generation of diversity in malaria parasites.</a> Current Opinion in Microbiology. 15 (4), 456-462 (2012).</li><li>Lee, A. H., Symington, L. S., Fidock, D. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=DNA+Repair+Mechanisms+and+Their+Biological+Roles+in+the+Malaria+Parasite+Plasmodium+falciparum.">DNA Repair Mechanisms and Their Biological Roles in the Malaria Parasite Plasmodium falciparum.</a> Microbiology and Molecular Biology Reviews. 78 (3), 469-486 (2014).</li><li>Cobb, D. 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=The+Exported+Chaperone+PfHsp70x+Is+Dispensable+for+the+Plasmodium+falciparum+Intraerythrocytic+Life+Cycle.">The Exported Chaperone PfHsp70x Is Dispensable for the Plasmodium falciparum Intraerythrocytic Life Cycle.</a> mSphere. 2 (5), (2017).</li><li>Prommana, P., 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=Inducible+knockdown+of+Plasmodium+gene+expression+using+the+glmS+ribozyme.">Inducible knockdown of Plasmodium gene expression using the glmS ribozyme.</a> Public Library of Science One. 8 (8), e73783 (2013).</li><li>Ganesan, S. M., Falla, A., Goldfless, S. J., Nasamu, A. S., Niles, J. 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E., 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=Plasmodium+food+vacuole+plasmepsins+are+activated+by+falcipains.">Plasmodium food vacuole plasmepsins are activated by falcipains.</a> Journal of Biological Chemistry. 283 (19), 12870-12876 (2008).</li><li>Wu, Y., Sifri, C. D., Lei, H. -. H., Su, X. -. Z., Wellems, T. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Transfection+of+Plasmodium+falciparum+within+human+red+blood+cells.">Transfection of Plasmodium falciparum within human red blood cells.</a> Proceedings of the National Academy of Sciences USA. 92, 973-977 (1995).</li><li>Janse, C. 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=High+efficiency+transfection+of+Plasmodium+berghei+facilitates+novel+selection+procedures.">High efficiency transfection of Plasmodium berghei facilitates novel selection procedures.</a> Molecular and Biochemical Parasitology. 145 (1), 60-70 (2006).</li><li>Counihan, N. A., 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=Plasmodium+falciparum+parasites+deploy+RhopH2+into+the+host+erythrocyte+to+obtain+nutrients,+grow+and+replicate.">Plasmodium falciparum parasites deploy RhopH2 into the host erythrocyte to obtain nutrients, grow and replicate.</a> eLife. 6, (2017).</li><li>Klemba, M., Beatty, W., Gluzman, I., Goldberg, D. 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The implementation of CRISPR/Cas9 in P. falciparum has both increased the efficiency of and decreased the amount of time needed for modifying the parasite&#39;s genome, compared to previous methods of genetic manipulation. This comprehensive protocol outlines the steps necessary for generating conditional mutants using CRISPR/Cas9 in P. falciparum. While the method here is geared specifically for the generation of HA-glmS mutants, this strategy can be adapted for a variety of needs, including t...

Malaria is a devastating disease caused by protozoan parasites of the genus Plasmodium. P. falciparum, the most deadly human malaria parasite, causes approximately 445,000 deaths per year, mostly in children under the age of five1. Plasmodium parasites have an intricate life cycle involving a mosquito vector and a vertebrate host. Humans first become infected when an infected mosquito takes a blood meal. Then, the parasite invades the liver where it grows, develops, and divides for approximately one week.After this process, the parasites are released into the bloodstream, where they undergo asexual replication in red blood cells (RBCs). Growth of the parasites within the RBCs are directly responsible for the clinical symptoms associated with malaria2.
Until recently, production of transgenic P. falciparum was a laborious process, involving several rounds of drug selection that took many months and had a high failure rate. This time-consuming procedure relieson the generation of random DNA breaks in the region of interest and the endogenous ability of the parasite to mend its genome though homologous repair3,4,5,6. Recently, Clustered Regularly Interspaced Palindromic Repeat/Cas9 (CRISPR/Cas9) genome editing has been successfully utilized in P. falciparum7,8. The introduction of this new technology in malaria research has been critical for advancing understanding of the biology of these deadly Plasmodium parasites. CRISPR/Cas9 allows for specific targeting of genes through guide RNAs (gRNAs) that are homologous to the gene of interest. The gRNA/Cas9 complex recognizes the gene through the gRNA, and Cas9 then introduces a double-strand break, forcing the initiation of repair mechanisms in the organism9,10. Because P. falciparum lacks the machinery to repair DNA breaks through non-homologous end joining, it utilizes homologous recombination mechanisms and integrates transfected homologous DNA templates to repair the Cas9/gRNA-induced double-strand break11,12.
Here, we present a protocol for the generation of conditional knockdown mutants in P. falciparum using CRISPR/Cas9 genome editing. The protocol demonstrates usage of the glmS ribozyme to conditionally knockdown protein levels of PfHsp70x (PF3D7_0831700), a chaperone exported by P. falciparum into host RBCs13,14. The glmS ribozyme is activated by treatment with glucosamine (which is converted to glucosamine-6-phosphate in cells) to cleave its associated mRNA, leading to a reduction in the protein14. This protocol can be easily adapted to utilize other conditional knockdown tools, such as destabilization domains or RNA aptamers4,5,15. Our protocol details the generation of a repair plasmid consisting of a hemagglutinin (HA) tag and glmS ribozyme coding sequence flanked by sequences that are homologous to the PfHsp70x open reading frame (ORF) and 3&#39;-UTR. We also describe the generation of a second plasmid to drive expression of the gRNA. These two plasmids, along with a third that drives expression of Cas9, are transfected into RBCs and used to modify the genome of P. falciparum parasites. Finally, we describe a polymerase chain reaction (PCR)-based technique to verify integration of the tag and glmS ribozyme. This protocol is highly adaptable for the modification or complete knockout of any P. falciparum genes, enhancing our ability to generate new insights into the biology of the malaria parasite.

<table>
	<tbody>
		<tr>
			<td>Gene Pulser Xcell Electroporator</td>
			<td>Bio-Rad</td>
			<td>1652660</td>
			<td></td>
		</tr>
		<tr>
			<td>Gene Pulser Xcell Electroporator</td>
			<td>Bio-Rad</td>
			<td>165-2086</td>
			<td>We buy the ones that are individually wrapped</td>
		</tr>
		<tr>
			<td>Sodium Acetate</td>
			<td>Sigma-Aldrich</td>
			<td>S2889-250g</td>
			<td></td>
		</tr>
		<tr>
			<td>DSM1</td>
			<td>Gift from Akhil Vaidya lab</td>
			<td>Ganesan et al. Mol. Biochem. Parasitol. 2011 177:29-34</td>
			<td></td>
		</tr>
		<tr>
			<td>TPP Tissue Culture 6 Well Plates</td>
			<td>MIDSCI</td>
			<td>TP92006</td>
			<td></td>
		</tr>
		<tr>
			<td>TPP 100mm Tissue Culture Dishes (12 mL Plate)</td>
			<td>MIDSCI</td>
			<td>TP93100</td>
			<td></td>
		</tr>
		<tr>
			<td>TPP Tissue Culture 96 Well Plates</td>
			<td>MIDSCI</td>
			<td>TP92096</td>
			<td></td>
		</tr>
		<tr>
			<td>TPP Tissue Culture 24 Well Plates</td>
			<td>MIDSCI</td>
			<td>TP92024</td>
			<td></td>
		</tr>
		<tr>
			<td>NEBuffer 2</td>
			<td>New England Biolabs</td>
			<td>#B7002S</td>
			<td></td>
		</tr>
		<tr>
			<td>NEBuffer 2.1</td>
			<td>New England Biolabs</td>
			<td>#B7202S</td>
			<td></td>
		</tr>
		<tr>
			<td>BtgZI</td>
			<td>New England Biolabs</td>
			<td>#R0703L</td>
			<td></td>
		</tr>
		<tr>
			<td>SacII</td>
			<td>New England Biolabs</td>
			<td>#R0157L</td>
			<td></td>
		</tr>
		<tr>
			<td>HindIII-HF</td>
			<td>New England Biolabs</td>
			<td>#R3104S</td>
			<td></td>
		</tr>
		<tr>
			<td>Afe1</td>
			<td>New England Biolabs</td>
			<td>#R0652S</td>
			<td></td>
		</tr>
		<tr>
			<td>Nhe1-HF</td>
			<td>New England Biolabs</td>
			<td>#R3131L</td>
			<td></td>
		</tr>
		<tr>
			<td>T4 DNA Polymerase</td>
			<td>New England Biolabs</td>
			<td>#M0203S</td>
			<td></td>
		</tr>
		<tr>
			<td>500 mL Steritop bottle top filter unit</td>
			<td>Millipore</td>
			<td>SCGPU10RE</td>
			<td>You can use any size that fits your needs</td>
		</tr>
		<tr>
			<td>EGTA</td>
			<td>Sigma</td>
			<td>E4378-100G</td>
			<td></td>
		</tr>
		<tr>
			<td>KCl</td>
			<td>Sigma-Aldrich</td>
			<td>P9333-500g</td>
			<td></td>
		</tr>
		<tr>
			<td>CaCl2</td>
			<td>Sigma-Aldrich</td>
			<td>C7902-500g</td>
			<td></td>
		</tr>
		<tr>
			<td>MgCl2</td>
			<td>Sigma-Aldrich</td>
			<td>M8266-100g</td>
			<td></td>
		</tr>
		<tr>
			<td>K2HPO4</td>
			<td>Fisher</td>
			<td>P288-500</td>
			<td></td>
		</tr>
		<tr>
			<td>HEPES</td>
			<td>Sigma-Aldrich</td>
			<td>H4034-500g</td>
			<td></td>
		</tr>
		<tr>
			<td>pMK-U6</td>
			<td>Generated by the Muralidharan Lab</td>
			<td>n/a</td>
			<td></td>
		</tr>
		<tr>
			<td>pHA-glmS</td>
			<td>Generated by the Muralidharan Lab</td>
			<td>n/a</td>
			<td></td>
		</tr>
		<tr>
			<td>pUF1-Cas9</td>
			<td>Gift from the Jose-Juan Lopez-Rubio Lab</td>
			<td>Ghorbal et al. Nature Biotech 2014</td>
			<td></td>
		</tr>
		<tr>
			<td>Glucose</td>
			<td>Sigma-Aldrich</td>
			<td>G7021-1KG</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium bicarbonate</td>
			<td>Sigma-Aldrich</td>
			<td>S5761-500G</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium pyruvate</td>
			<td>Sigma-Aldrich</td>
			<td>P5280-100G</td>
			<td></td>
		</tr>
		<tr>
			<td>Hypoxanthine</td>
			<td>Sigma-Aldrich</td>
			<td>H9636-25g</td>
			<td></td>
		</tr>
		<tr>
			<td>Gentamicin Reagent</td>
			<td>Gibco</td>
			<td>15710-064</td>
			<td></td>
		</tr>
		<tr>
			<td>Thymidine</td>
			<td>Sigma-Aldrich</td>
			<td>T1895-1G</td>
			<td></td>
		</tr>
		<tr>
			<td>PL6-eGFP BSD</td>
			<td>Generated by the Muralidharan Lab</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Puf1-cas9 eGFP gRNA</td>
			<td>Generated by the Muralidharan Lab</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>NucleoSpin Gel and PCR Clean-up</td>
			<td>Macherey-Nagel</td>
			<td>740609.250</td>
			<td></td>
		</tr>
		<tr>
			<td>Albumax I</td>
			<td>Life Technologies</td>
			<td>N/A</td>
			<td>You will want to try a few batches to find out what the parasites will grow in best</td>
		</tr>
		<tr>
			<td>Human Red Blood Cells</td>
			<td>Interstate Blood Bank, Inc</td>
			<td>Email or call them directly for ordering</td>
			<td>We typically use O+ blood</td>
		</tr>
		<tr>
			<td>3D7 parasite line</td>
			<td>Available upon request</td>
			<td>N/A</td>
			<td></td>
		</tr>
		<tr>
			<td>Lysogeny Broth (LB)</td>
			<td>Fisher</td>
			<td>BP1426-2</td>
			<td>You can make your own, it is not necessary to use exactly this</td>
		</tr>
		<tr>
			<td>Ampicilin</td>
			<td>Fisher</td>
			<td>BP1760-25</td>
			<td>We make a 1000X stock at 100mg/ml in water and store in the -20C</td>
		</tr>
		<tr>
			<td>Ampicilin</td>
			<td>Clonetech</td>
			<td>R050A</td>
			<td></td>
		</tr>
		<tr>
			<td>Anti-EF1alpha</td>
			<td>Dr. Daniel Goldberg&#39;s Lab</td>
			<td>Washington University in St. Louis</td>
			<td>You can use your preferred loading control for western blots. This is just the one we use in our laboratory</td>
		</tr>
		<tr>
			<td>Rat Anti-HA Clone 3F10, monoclonal</td>
			<td>Made by Roche, sold by Sigma</td>
			<td>11867423001</td>
			<td>You can use your preferred anti-HA antibody</td>
		</tr>
		<tr>
			<td>0.6 mL tubes</td>
			<td>Fisher</td>
			<td>AB0350</td>
			<td></td>
		</tr>
		<tr>
			<td>Fisher HealthCare* PROTOCOL* Hema 3* Manual Staining System (Fixative+Solution I and II)</td>
			<td>Fisher</td>
			<td>22-122-911</td>
			<td>You can also use giemsa stain</td>
		</tr>
		<tr>
			<td>Fisherfines Premium Frosted Microscope Slides - Size: 3 x 1 in.</td>
			<td>Fisher</td>
			<td>12-544-3</td>
			<td></td>
		</tr>
	</tbody>
</table>

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.

A schematic of the plasmids used in this method as well as an example of a shield mutation are shown in Figure 1. As an example of how to identify mutant parasites after transfection, results from PCRs for checking integration of the HA-glmS construct are shown in Figure 2. A representative image of a cloning plate is shown in Figure 3 to demonstrate the color change of the medium in the pre...

Watch this Scientific Journal Video about CRISPR/Cas9 Gene Editing to Make Conditional Mutants of Human Malaria Parasite P. falciparum at JoVE.com

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.

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 ...

This method can help answer key questions in the biology of the human malaria parasite, P.Falciparum, by helping to uncover protein function through conditional knockdown. The main advantage of this technique is that it allows for relatively easy generation of conditional mutants as compared to previous methods. To begin, go to Chop Chop and select Fasta Target'Under Target, paste the 200 base pairs from the three prime end of the open reading frame of a gene and 200 base pairs from the start of the gene's three prime UTR.Under In'select P.Falciparum'and select CRISPR/Cas9'under Using'Next, click Find Target Sites'Select a gRNA sequence from the options presented, giving preference to the most efficient gRNA that is closest to the site of modification and that has the fewest off-target sites. Purchase the gRNA sequence and its reverse complement as polyacrylamide gel electrophoresis purified oligos. The gRNA sequence used to target PfH-sp70x can be found in the text protocol.Add 40 micrograms each of pMK-U6, pUF1-Cas9, and pHA-glmS DNA into a sterile 1.5 millimeter centrifuge tube. Add one-tenth of the volume of DNA of three molar sodium acetate in water to the tube and mix it well using a vortex. Then, add 2.5 times the volume of 100 percent ethanol to the tube and mix it well using a vortex for at least 30 seconds.Place the tube on ice or at minus 20 degrees Celsius for 30 minutes. Then, centrifuge the tube at 18, 300 times G for 30 minutes at four degrees Celsius. Following centrifugation, carefully remove the supernatant from the tube without disturbing the pellet.Add three times the volume of 70 percent ethanol to the tube and mix it briefly using a vortex. Centrifuge the tube at 18, 300 times G for 30 minutes at four degrees Celsius. Again, carefully remove the supernatant from the tube without disturbing the pellet.Leave the tube open and allow the pellet to air dry for 15 minutes. Store the precipitated DNA at minus 20 degrees Celsius until it is needed for transfection. To transfect RBCs, prepare 1X cytomix buffer as well as incomplete and complete RPMI as described in the text protocol.Filter sterilize the buffer using a 0.22 micron filter. Add 380 microliters of the 1X cytomix to the DNA and vortex to dissolve. Allow the DNA to dissolve in the 1X cytomix for 10 minutes, vortexing every three minutes for 10 seconds.In a sterile, 15 milliliter conical tube, combine 300 microliters of isolated human RBCs in the incomplete RPMI with four milliliters of 1X cytomix. Centrifuge the RBCs at 870 times G for three minutes. Then remove the supernatant from the RBC pellet.Re-suspend the RBC pellet with the DNA-cytomix mixture and transfer it to a 0.2 centimeter electroporation cuvette. Porate the RBCs using the conditions listed in the text protocol. Following electroporation, transfer the contents from the cuvette to a 15 milliliter conical tube containing five milliliters of complete RPMI.Centrifuge the tube at 870 times G for three minutes at 20 degrees Celsius. Then, decant the supernatant. Now, re-suspend the pellet in four milliliters of complete RPMI and transfer to one well in a six-well tissue culture plate.Add 400 microliters of a high schizont culture to the transferred RBCs. Maintain all the cultures at 37 degrees Celsius under three percent oxygen, three percent CO2, and 94 percent nitrogen. The next day, wash the culture with four milliliters of complete RPMI.Centrifuge the culture at 870 times G for three minutes. Aspirate the supernatant. Re-suspend the culture in four milliliters of complete RPMI.48 hours later, wash the culture with four milliliters of complete RPMI. Then, re-suspend the culture in complete RPMI containing one micromolar DSM1 to select for the Cas9 plasmid. After this point, replace the culture medium with fresh complete RPMI plus one micromolar DSM1 every 48 hours.Continue washing the cultures each day with complete RPMI until parasites are no longer visible by blood smear. To make a blood smear, pipette 150 microliters of culture into a 0.6 milliliter centrifuge tube. After pelleting the cells by centrifugation at 1, 700 times G for 30 seconds, aspirate off the supernatant.Use a pipette to transfer the pelleted cells to a glass slide. Using a second glass slide held at a 45 degree angle to the first slide, smear the blood droplet. Stain the slide using a commercially available staining kit according to the manufacturer's protocol.View the parasites using 100 times oil-immersion objective. Beginning five days post-transfection, remove two milliliters of the culture with RBCs re-suspended in the culture medium. Add back two milliliters of fresh medium and blood at two percent hematocrit.Add fresh blood in this manner once a week until parasite reappear, as determined by thin blood smear. Perform serial dilutions of the parasite culture to achieve a final concentration of 0.5 parasites per 200 microliters. Add 200 microliters of the diluted culture to the wells of a 96-well tissue culture plate.Maintain the cloning plate until parasites are detectable in the wells. Every 48 hours, replace the medium in the 96-well plate with fresh medium. Once a week, starting five days after beginning the cloning plate, remove 100 microliters from each well and add back 100 microliters of fresh medium plus blood.To identify any wells containing parasites, place the 96-well plate at a 45 degree angle for approximately 20 minutes, allowing the blood to settle at an angle within the plate. Then, place the 96-well plate on a light box. Notice that the wells containing parasites contain media that is yellow in color, compared to the pink media of parasite-free wells, due to acidification of the medium by the parasites.Using a serological pipette, move the contents of the parasite-containing wells to a 24-well tissue culture plate to allow expansion of the parasitemia. Using PCR analysis, check these clonal parasite lines for correct integration. The results of an immunofluorescence assay are shown here, demonstrating the successfully HA tagging of PfH-sp70x.PfH-sp70x glmS parasites were fixed and stained with DAPI as a nucleus marker, as well as antibodies to HA.Membrane-associated histidine rich protein one, a marker of protein export to the host RBC. A Western Blot analysis of PfH-sp70x protein level after treatment with glucosamine is shown here. As expected, the protein level decreases during the duration of treatment.This technique paves the way for researchers in the field of parasitology to investigate fundamental questions in the biology of the malaria parasite. It's important to remember that P.Falciparum is a blood-borne pathogen and appropriate personal protective equipment should be worn while performing this procedure.

crisprcas9-gene-editing-to-make-conditional-mutants-human-malaria

Research

JoVE Journal

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 ...

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 ...

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 ...

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 ...

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. ...

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

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

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

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

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

CRISPR/Cas9 Ribonucleoprotein-mediated Precise Gene Editing by Tube Electroporation

Gene editing nucleases, represented by CRISPR-associated protein 9 (Cas9), are becoming mainstream tools in biomedical research. Successful delivery of CRISPR/Cas9 elements into the target cells by transfection is a prerequisite for efficient gene editing. This protocol demonstrates that tube electroporation (TE) machine-mediated delivery of CRISPR/Cas9 ribonucleoprotein (RNP), along with single-stranded oligodeoxynucleotide (ssODN) donor templates to different types of mammalian cells, leads to robust precise gene editing events. First, TE was applied to deliver CRISPR/Cas9 RNP and ssODNs to induce disease-causing mutations in the interleukin 2 receptor subunit gamma (IL2RG) gene and sepiapterin reductase (SPR) gene in rabbit fibroblast cells. Precise mutation rates of 3.57%-20% were achieved as determined by bacterial TA cloning sequencing. The same strategy was then used in human iPSCs on several clinically relevant genes including epidermal growth factor receptor (EGFR), myosin binding protein C, cardiac (Mybpc3), and hemoglobin subunit beta (HBB). Consistently, highly precise mutation rates were achieved (11.65%-37.92%) as determined by deep sequencing (DeepSeq). The present work demonstrates that tube electroporation of CRISPR/Cas9 RNP represents an efficient transfection protocol for gene editing in mammalian cells.

Presented here is a protocol for efficient CRISPR/Cas9 ribonucleoprotein-mediated gene editing in mammalian cells using tube electroporation.

Gene editing nucleases, represented by CRISPR-associated protein 9 (Cas9), are becoming mainstream tools in biomedical research. Successful delivery of ...

Introducing a Gene Knockout Directly Into the Amastigote Stage of Trypanosoma cruzi Using the CRISPR/Cas9 System

Trypanosoma cruzi is a pathogenic protozoan parasite that causes Chagas&#8217; disease mainly in Latin America. In order to identify a novel drug target against T. cruzi, it is important to validate the essentiality of the target gene in the mammalian stage of the parasite, the amastigote. Amastigotes of T. cruzi replicate inside the host cell; thus, it is difficult to conduct a knockout experiment without going through other developmental stages. Recently, our group reported a growth condition in which the amastigote can replicate axenically for up to 10 days without losing its amastigote-like properties. By using this temporal axenic amastigote culture, we successfully introduced gRNAs directly into the Cas9-expressing amastigote to cause gene knockouts and analyzed their phenotypes exclusively in the amastigote stage. In this report, we describe a detailed protocol to produce in vitro derived extracellular amastigotes, and to utilize the axenic culture in a CRISPR/Cas9-mediated knockout experiment. The growth phenotype of knockout amastigotes can be evaluated either by cell counts of the axenic culture, or by replication of intracellular amastigote after host cell invasion. This method bypasses the parasite stage differentiation normally involved in producing a transgenic or a knockout amastigote. Utilization of the temporal axenic amastigote culture has the potential to expand the experimental freedom of stage-specific studies in T. cruzi.

Introducing a Gene Knockout Directly Into the Amastigote Stage of Trypanosoma cruzi Using the CRISPR/Cas9 System

Here, we describe a protocol to introduce a gene knockout into the extracellular amastigote of Trypanosoma cruzi, using the CRISPR/Cas9 system. The growth phenotype can be followed up either by cell counting of axenic amastigote culture or by proliferation of intracellular amastigotes after host cell invasion.

Trypanosoma cruzi is a pathogenic protozoan parasite that causes Chagas&#8217; disease mainly in Latin America. In order to identify a novel drug target ...

CRISPR-Cas9-Mediated Genome Editing in the Filamentous Ascomycete Huntiella omanensis

The CRISPR-Cas9 genome editing system is a molecular tool that can be used to introduce precise changes into the genomes of model and non-model species alike. This technology can be used for a variety of genome editing approaches, from gene knockouts and knockins to more specific changes like the introduction of a few nucleotides at a targeted location. Genome editing can be used for a multitude of applications, including the partial functional characterization of genes, the production of transgenic organisms and the development of diagnostic tools. Compared to previously available gene editing strategies, the CRISPR-Cas9 system has been shown to be easy to establish in new species and boasts high efficiency and specificity. The primary reason for this is that the editing tool uses an RNA molecule to target the gene or sequence of interest, making target molecule design straightforward, given that standard base pairing rules can be exploited. Similar to other genome editing systems, CRISPR-Cas9-based methods also require efficient and effective transformation protocols as well as access to good quality sequence data for the design of the targeting RNA and DNA molecules. Since the introduction of this system in 2013, it has been used to genetically engineer a variety of model species, including Saccharomyces cerevisiae, Arabidopsis thaliana, Drosophila melanogaster and Mus musculus. Subsequently, researchers working on non-model species have taken advantage of the system and used it for the study of genes involved in processes as diverse as secondary metabolism in fungi, nematode growth and disease resistance in plants, among many others. This protocol detailed below describes the use of the CRISPR-Cas9 genome editing protocol for the truncation of a gene involved in the sexual cycle of Huntiella omanensis, a filamentous ascomycete fungus belonging to the Ceratocystidaceae family.

CRISPR-Cas9-Mediated Genome Editing in the Filamentous Ascomycete Huntiella omanensis

The CRISPR-Cas9 genome editing system is an easy-to-use genome editor that has been used in model and non-model species. Here we present a protein-based version of this system that was used to introduce a premature stop codon into a mating gene of a non-model filamentous ascomycete fungus.

The CRISPR-Cas9 genome editing system is a molecular tool that can be used to introduce precise changes into the genomes of model and non-model species ...