lexAop and UAS regulatory sequences and a minimal Hsp70 promoter (derived from the pUASTLOTattB vector) are fused upstream of a fusion protein that encodes an basolaterally localized nanobody-based GFP trap for extracellular proteins. The fusion protein contains the nrv1 coding sequence (from the LD02379 cDNA clone) with a TagBFP fluorescent tag inserted near the N-terminal end (between the first and second exon). In addition, the GFP-binding VHH(GFP4) nanobody has been inserted at the C-terminal end of the nrv1 coding sequence. The VHH(GFP4) nanobody faces the extracellular space. The lexAop and UAS regulatory sequences are flanked by loxP and lox2272 sites respectively (meaning that the P1cre recombinase can be used to excise one of the enhancers in a mutually exclusive manner if desired).