Sequence comprised of 1: a loxP cassette containing a w+* marker and 2: the splice acceptor site of a Trf intron (the intron that is normally upstream of the protein-coding exons) followed by the coding sequence of the short (p75) Trf2 isoform and an SV40 polyadenylation signal, has been inserted into the attP site present in TI{TI}Trf2mCherry.attP. This results in a Trf2 locus that can only produce the short isoform. The loxP cassette containing a Disc\RFPmCherry.Act5C marker that was present on the TI{TI}Trf2mCherry.attP chromosome is also still present in the Trf2 intron, upstream of the newly inserted sequence.