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      Efficient Genome Engineering of Toxoplasma gondii Using CRISPR/Cas9

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          Abstract

          Toxoplasma gondii is a parasite of humans and animals, and a model for other apicomplexans including Plasmodium spp., the causative agents of malaria. Despite many advances, manipulating the T. gondii genome remains labor intensive, and is often restricted to lab-adapted strains or lines carrying mutations that enable selection. Here, we use the RNA-guided Cas9 nuclease to efficiently generate knockouts without selection, and to introduce point mutations and epitope tags into the T. gondii genome. These methods will streamline the functional analysis of parasite genes and enable high-throughput engineering of their genomes.

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          Most cited references13

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          Tagging of endogenous genes in a Toxoplasma gondii strain lacking Ku80.

          As with other organisms with a completed genome sequence, opportunities for performing large-scale studies, such as expression and localization, on Toxoplasma gondii are now much more feasible. We present a system for tagging genes endogenously with yellow fluorescent protein (YFP) in a Deltaku80 strain. Ku80 is involved in DNA strand repair and nonhomologous DNA end joining; previous studies in other organisms have shown that in its absence, random integration is eliminated, allowing the insertion of constructs with homologous sequences into the proper loci. We generated a vector consisting of YFP and a dihydrofolate reductase-thymidylate synthase selectable marker. The YFP is preceded by a ligation-independent cloning (LIC) cassette, which allows the insertion of PCR products containing complementary LIC sequences. We demonstrated that the Deltaku80 strain is more effective and efficient in integrating the YFP-tagged constructs into the correct locus than wild-type strain RH. We then selected several hypothetical proteins that were identified by a proteomic screen of excreted-secreted antigens and that displayed microarray expression profiles similar to known micronemal proteins, with the thought that these could potentially be new proteins with roles in cell invasion. We localized these hypothetical proteins by YFP fluorescence and showed expression by immunoblotting. Our findings demonstrate that the combination of the Deltaku80 strain and the pYFP.LIC constructs reduces both the time and cost required to determine localization of a new gene of interest. This should allow the opportunity for performing larger-scale studies of novel T. gondii genes.
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            A novel epitope tag system to study protein targeting and organelle biogenesis in Trypanosoma brucei.

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              Conditional genome engineering in Toxoplasma gondii uncovers alternative invasion mechanisms

              We established a conditional site–specific recombination system based on dimerizable Cre–mediated recombination in the apicomplexan parasite Toxoplasma gondii. Using a novel single vector strategy that allows ligand-dependent, efficient removal of a gene of interest, we generated three knockouts of apicomplexan genes considered essential for host-cell invasion. Our findings uncover the existence of an alternative invasion pathway in apicomplexan parasites.
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                Author and article information

                Contributors
                Role: Editor
                Journal
                PLoS One
                PLoS ONE
                plos
                plosone
                PLoS ONE
                Public Library of Science (San Francisco, USA )
                1932-6203
                2014
                27 June 2014
                : 9
                : 6
                : e100450
                Affiliations
                [1 ]Whitehead Institute for Biomedical Research, Cambridge, Massachusetts, United States of America
                [2 ]School of Chemistry and Biomedical Sciences Research Complex, University of St. Andrews and EaStCHEM, North Haugh, St Andrews, Fife, Scotland, United Kingdom
                University at Buffalo, United States of America
                Author notes

                Competing Interests: The authors have declared that no competing interests exist.

                Conceived and designed the experiments: SMS SL. Performed the experiments: SMS CGH SL. Analyzed the data: SMS SL. Contributed reagents/materials/analysis tools: FT NJW. Contributed to the writing of the manuscript: SMS SL.

                Article
                PONE-D-14-14026
                10.1371/journal.pone.0100450
                4074098
                24971596
                b59d0250-4fa8-4d79-99ff-810056c18e68
                Copyright @ 2014

                This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

                History
                : 28 March 2014
                : 23 May 2014
                Page count
                Pages: 8
                Funding
                This work was supported in part by NIH grant 1DP5OD017892 to S.L. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
                Categories
                Research Article
                Biology and Life Sciences
                Parasitology
                Parasite Groups
                Apicomplexa
                Tachyzoites
                Custom metadata
                The authors confirm that all data underlying the findings are fully available without restriction. All relevant data are within the paper and its Supporting Information files.

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