“We detected TagRFP expression in cells in the ganglion cell layer (GCL) in the retina (arrowheads, Figure 2—figure supplement 3), in which robust shha expression was previously reported (Shkumatava et al., 2004). […] It is of interest to examine whether TagRFP expression would be enhanced in the target tissues by modifying the 2A sequence of Zwitch to include a glycine-serine-glycine spacer (GSG), which was recently found to significantly improve the cleavage efficiency of the 2A peptide (Wang et al., 2015b).”