Universal Single Copy Knock-In System in Caenorhabditis elegans: One Plasmid to Target All Chromosomes

Abstract

Successful transgenesis in model organisms has dramatically helped us understand gene function, regulation, genetic networks, and potential applications. Here, we introduce the universal single-copy knock-in system (Universal SKI System or U-SKI), designed for inserting any transgene by CRISPR/Cas9 in the Caenorhabditis elegans genome. The Universal SKI System takes advantage of a plasmid (pSKI), which can also be used for extrachromosomal arrays, to facilitate the insertion of a transgene at specific safe harbor loci on each autosomal chromosome. The pSKI plasmid contains multiple restriction sites for easy cloning and serves as a CRISPR/Cas9-based insertion repair template because it has two synthetic and long homology arms that recombine with the SKI cassettes. This system also uses a single crRNA guide, which acts as a Co-CRISPR enrichment marker. Overall, the Universal SKI System is highly flexible; with the same Universal SKI cassette on each autosome, researchers can select the insertion site and streamline tracking while reducing the complexity of expressing single-copy transgenes in C. elegans.