Cloning-Free Genome Editing by CRISPR/T7RNAP/Cas9 in Trypanosoma cruzi

The genetic manipulation of the human parasite Trypanosoma cruzi has been significantly improved since the implementation of the CRISPR/Cas9 technology for genome editing in this organism. Initially, the system was successfully used for gene knockout and endogenous C-terminal tagging in T. cruzi. Recently, an updated version of this technology has been used for gene complementation, site-directed mutagenesis, and N-terminal tagging in trypanosomatids. This cloning-free strategy, called CRISPR/T7RNAP/Cas9, is extremely useful for identifying essential genes when null mutants are not viable. Mutant cell lines obtained by this new system have been used for the functional characterization of proteins in different developmental stages of this parasite's life cycle, including infective trypomastigotes and intracellular amastigotes. In this chapter, we describe the methodology to achieve genome editing by CRISPR/T7RNAP/Cas9 in T. cruzi. Our method involves the generation of T. cruzi epimastigotes that constitutively express the T7 RNA polymerase (T7RNAP) and SpCas9, and their co-transfection with an sgRNA template and donor DNA(s) as polymerase chain reaction (PCR) products. Using this strategy, we have generated genetically modified parasites in 2-3 weeks without the need for gene cloning, cell sorting, or having to perform several transfection attempts to verify the sgRNA efficiency for targeting the gene of interest. The methodology has been organized according to three main genetic purposes: gene knockout, gene complementation of knockout cell lines, and endogenous (N- or C-terminal) tagging in T. cruzi.