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. (Generated by P1cre-mediated excision of the lexAop regulatory sequences present in nrv1^{lexAop.UAS.GrabFP.B.Ext.TagBFP}).