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 in which the Mmus\Robo2 Ig1 domain has been replaced with the Ig1 domain of robo1 (the encoded protein contains amino acids 55-152 of robo1 fused to amino acids 131-1508 of Mmus\Robo2). 2192bp of robo1 downstream flanking sequence is also present.