UAS regulatory sequences are fused upstream of a genomic fragment that encompasses the coding sequence of mud isoform RF (one of the longer isoforms that does not include a Pins binding domain (PBD)), and in which sequence that includes the PBD-containing exons and the the exon specific to the PBD-lacking shorter isoforms (isoforms RG and RK) has been deleted, so that only the longer PBD-lacking isoform can be produced. The coding sequence is tagged at the N-terminal end with Tag:FLAG.