A synthetic intron (constitutively spliced in all tissues and at all stages) from P{GI} has been inserted between the Tag:MYC tag and GFP(S65T) coding region in Avic\GFPUGH.S65T.Ubi-p63E.Tag:MYC, such that splicing of the intron is necessary for production of functional GFP(S65T) protein.