Protocol for efficient CRISPR-Cas9-mediated fluorescent tag knockin in hard-to-transfect erythroid cell lines

Precise insertion of fluorescent tags by CRISPR-Cas9-mediated homologous recombination (HR) in mammalian genes is a powerful tool allowing to study gene function and protein gene products. Here, we present a protocol for efficient HR-mediated targeted insertion of fluorescent markers in the genome of hard-to-transfect erythroid cell lines MEL (mouse erythroleukemic) and MEDEP (mouse ES cell-derived erythroid progenitor line). We describe steps for plasmid construction, electroporation, amplification, and verification of genome editing. We then detail procedures for isolating positive clones and validating knockin clones. For complete details on the use and execution of this protocol, please refer to Deleuze et al.1.