2385bp of robo1 sequence (including the promoter and endogenous signal sequence) is fused upstream of four copies of Tag:HA followed by sequence encoding a chimeric receptor composed of robo1 amino acids 52-890 and Cele\sax-3 amino acids 847-1273 (coordinates relative to GenBank accessions AAF46887.1 (robo1) and AAC38848.1 (Cele\sax-3)). 2192bp of robo1 downstream flanking sequence is also present.