UAS regulatory sequences are fused upstream of a genomic fragment that encompasses the coding sequence of the Pins binding domain (PBD)-containing isoforms of mud, and in which sequence that encodes the exon specific to the PBD-lacking shorter isoforms (isoforms RG and RK) has been deleted, so that only the PBD-containing isoforms can be produced. The coding sequence is tagged at the N-terminal end with Tag:FLAG.