Modern approaches to engineering human reporter cell lines using CRISPR within Safe Harbor loci and endogenous genes

Reporter systems are gaining increasing popularity in modern molecular biology as they provide reliable and clear readouts for various types of assays, both in cellulo and in vivo. The generation of reporter cell lines is instrumental for screening activators and inhibitors of signaling pathways to develop new therapeutic approaches. Reporter cell lines are those with stably integrated reporter constructs containing signaling genes (often luciferase or fluorescent proteins), enabling the visualization and tracking of protein expression. Although seemingly harmless and straightforward, untargeted genomic integration of reporter genes may severely affect the expression of neighboring genes, causing unwanted and unpredictable effects. Unlike the untargeted approach, the CRISPR/Cas9 system provides a more precise method of reporter integration, especially when reporters are integrated into Safe Harbor loci. This ensures minimal influence on neighboring genomic regions. This review discusses recent advancements in creating reporter lines using the CRISPR/Cas9 system and experimental approaches for identifying suitable Safe Harbor loci.