ABSTRACT
The CRISPR (clustered regularly interspaced short palindromic repeats)-Cas (CRISPR-associated proteins) system is a gene-editing tool that mimics an adaptive immunity in prokaryotes to defend against invasive genetic elements in the form of viruses and plasmids. This bacterial immunity mechanism was revealed in the 1990s and early 2000s during genome sequencing efforts of archaeal and bacterial genomes. The CRISPR-Cas9 system is inherently present in 90% of archaea and 40% of prokaryotic cells, where it provides immunity against previously encountered invading nucleotides. As compared to other genome editing platforms such as TALENS, ZINC finger nuclease, and megaTALs, CRISPR-Cas9 is easily adaptable to a different application and species as only two components need to be delivered into the cell. CRISPR-Cas9 gene drives are highly efficient in performing gene edits. High efficiency of about 97% has been recorded in some studies using the CRISPR gene drive construct. The CRISPR platform is prone to off-target errors. This occurs in gene-editing endeavors as much as it may happen in gene drive projects. The principle of gene drives has often been applied to the cause of suppressing the population of disease vectors and pests, including building parasite resistance in vector populations. There are two kinds of gene drives that commonly use the CRISPR platform. The first one is the modification drive, which is used to alter wild-type alleles. The second kind is the suppression gene drive, which is used to reduce the population density or eradicate the organism. Generally, CRISPR-Cas systems provide a uniquely powerful gene-editing tool that is readily adaptable to newly encountered genomes. However, CRISPR gene editing is known to cause off-target effects that produce unintended negative effects. These off-target effects may arise from the gene-editing machinery targeting a similarly homologous sequence at a different location in the genome. CRISPR Cas9 gene drives are used for the eradication of vector-borne diseases in humans, crops, and livestock as well as population control of invasive species and crop and livestock pests.
