Figure 2. RFP signal in 661W cells transfected with the MEL-1B-R HDR plasmid. 661W cells were cotransfected with MEL-1B-R HDR and MEL-1B-R CRISPR/Cas9 KO. After 2–3 weeks of selection in medium containing puromycin, colonies were picked to become individual cell lines. Expression of red fluorescence protein indicates the successful homology directed insertion at the melatonin receptor type 2 (MT₂) locus. A: Bright-field. B: Bright-field plus red fluorescent protein (RFP). Scale bar = 100 µm.