Link to bioRxiv paper: http://biorxiv.org/cgi/content/short/2020.08.03.234252v1?rss=1 Authors: Ijaz, F., Ikegami, K. Abstract: Stable cell lines and animal models expressing tagged proteins are important tools for studying behaviors of cells and molecules. Several molecular biological technologies have been applied with varying degrees of success and efficiencies to establish cell lines expressing tagged proteins. Here we applied CRISPR/Cas9 for the knock-in of tagged proteins into the 5'UTR of the endogenous gene loci. With this 5'UTR-targeting knock-in strategy, stable cell lines expressing Arl13b-Venus, Reep6-HA, and EGFP-alpha-tubulin were established with high knock-in efficiencies ranging from 50 to 80%. The localization of the knock-in proteins were identical to that of the endogenous proteins in wild-type cells and showed homogenous expression. Moreover, the expression of knock-in EGFP-alpha-tubulin from the endogenous promoter was stable over long-term culture. We further demonstrated that the fluorescent signals were enough for a long time time-lapse imaging. The fluorescent signals were distinctly visible during the whole duration of the time-lapse imaging and showed specific subcellular localizations. Altogether, our strategy demonstrates that 5'UTR is a "hotspot" for targeted insertion of gene sequences and allows the stable expression of tagged proteins from endogenous loci in mammalian cells. Copy rights belong to original authors. Visit the link for more info