UASt regulatory sequences drive expression of a chimeric protein in which the robo1 cytoplasmic domain has been replaced by the cytoplasmic domain of drl (robo1 amino acids 52-939 are fused via a Leu-Ser-Phe-Arg linker to drl amino acids 265-610). The coding sequence is tagged at the N-terminal end with the Tag:SS(wg) signal sequence followed by seven copies of Tag:HA.