<p>A) The FlpO ORF contains two internal BsaI sites. These are mutated by amplifying fragments of the FlpO ORF via PCR. The primers contain flanking BsaI sites that lead to compatible overhangs after restriction digest. The site-directed mutagenesis vector (pGG-sdm) contains BsaI sites for the mutagenesis assembly. Additionally, BamHI and KpnI sites allow the transfer of the mutated DNA assembly to Golden Gate entry vectors. From there, mRNA can be generated using SP6 RNA polymerase. Note that the pGG-sdm vector represents a standard Gateway<sup>TM</sup> middle entry vector. B) A Golden Gate reaction is used to prepare a dual FRT-based recombination construct in the Gateway<sup>TM</sup> middle entry vector. An LR reaction was prepared to generate a final expression construct. ISceI sites flank the expression cassette. The dual FRT element is driven by the zebrafish beta actin 2 promoter and a human globin intron with SV40 polyA is used in the 3’ entry vector. C) Zebrafish embryos were injected with the expression construct alone or in combination with FlpO mRNA. Without FlpO mRNA 64% (n=98) of the fish were positively injected and showed eGFP expression and the absence of mCherry. In combination with FlpO mRNA 60% (n=79) of the fish were positively injected and all of them showed the complete absence of green fluorescence and the appearance of red fluorescence, which is indicative for proper FlpO activity.</p
