Introducing an Expanded Trinucleotide Repeat Tract into the Human Genome for Huntington's Disease Modeling In Vitro

In neurodegeneration studies, researchers are faced with problems such as limited material availability and late disease manifestation. Cell models provide the opportunity to investigate molecular mechanisms of pathogenesis. Moreover, genome editing technologies enable generation of isogenic cell models of hereditary diseases. Our protocol outlines an approach for introducing an expanded CAG repeat tract into the first exon of the HTT gene, the Huntington's disease causing mutation. The protocol allows modeling the disease at various severity levels by introducing different numbers of CAG repeats. Furthermore, the protocol can be applicable for modeling other diseases caused by trinucleotide repeat expansion. It is important to note there are many difficulties with cloning repeated sequences and amplification of GC-rich regions. Here, we also propose troubleshooting options, which overcome these problems. The protocol is based on CRISPR/Cas9-mediated homologous recombination with a uniquely designed donor plasmid harboring an expanded CAG tract flanked with long homology arms. © 2020 Wiley Periodicals LLC. Basic Protocol 1: Design and assembling donor and CRISPR/Cas9-expressing plasmids Basic Protocol 2: Transfection of cells with plasmids and sorting GFP-positive cells Basic Protocol 3: PCR screening single-cell clones and validation of the mutant HTT expression.