New TIGER Mouse Model Helps Advance Genetic Medicine

UC Irvine researchers have developed a new model for investigating precision-genome editing, helping advance methods to address many inherited and environmental disorders.

As CRISPR gene-editing technology continues to advance, letting scientists address inherited and environmental disorders, there is an increased need for suitable delivery systems to correct genes in vivo. A key hurdle is the safe and efficient delivery of CRISPR components to the target cells. Researchers thus need ways to effectively compare different delivery strategies for both viral and non-viral genome editors.

“Current genome-editing reporter models have shortcomings when it comes to evaluating genome-editor delivery, including the level of precision, level of sensitivity and ability to repurpose the method for other genome editor variants,” says Krzysztof Palczewski, PhD, of UC Irvine’s Brunson Center for Translational Vision Research and Gavin Herbert Eye Institute. “We developed a new reporter mouse called TIGER that can help benchmark current delivery strategies and validate new delivery strategies to advance genetic medicine.”

The work is outlined in a new paper, “TIGER: A tdTomato in vivo genome-editing reporter mouse for investigating precision-editor delivery approaches,” published in the Proceedings of the National Academy of Sciences (PNAS).

A New Genome Editing Reporter

TIGER is a novel reporter model, with single-cell resolution, that can evaluate and compare genome-editing delivery methods across the mouse body. It harbors an integrated and constitutively expressed mutated tdTomato gene in the Polr2a locus that abolishes fluorescence, but successful adenine base editing or prime editing restores tdTomato fluorescence.

“This construct should be stably expressed in every mouse tissue, and can be edited by traditional CRISPR, base editing or prime editing,” says Samuel Du, an MD/PhD candidate working in the Palczewski Lab and a National Eye Institute research fellow. “We demonstrate base and prime editing in seven therapeutically relevant cell types and four tissues.” Additionally, it is editable by two different Cas9 types, Staphylococcus aureus and Streptococcus pyogenes, so novel Cas9 variants can be studied with this mouse as well.

“Our mouse is rapid, quantitative and easy to analyze,” says Du. “We even show non-invasive analysis of living tissue in our mouse without tissue collection.”

Advancing Genetic Medicine

Through their experimental study, the researchers have shown successful delivery and editing to numerous therapeutically relevant tissue types in the mouse body, including many cell types in the eye, liver, skeletal muscle and brain.

“We intentionally designed this mouse to be useful to people studying any organ,” says Du. “Each tissue and cell type may require a different delivery strategy, so having a flexible system to compare each system will be invaluable to speed discovery.”

The team is already using TIGER to benchmark state-of-the-art strategies. “We’re also using this mouse to come up with new ideas that we can test side by side,” says Du. “We hope it will be an important resource for anyone studying genome editing.”