A cassette containing an EGFP reporter gene, PreScission protease cleavage site and several epitope tags (6 histidine, FLAG and 2 HA) was inserted into exon 1 at the ATG start site. Exon 2 was flanked by loxP sites. Flp-mediated recombination removed the FRT-flanked neomycin resistance cassette inserted upstream of exon 2.