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 apically enriched nanobody-based GFP trap for extracellular proteins. The fusion protein contains the T48 coding sequence with the GFP-binding VHH(GFP4) nanobody inserted near the N-terminal end. In addition, a mCherry fluorescent tag followed by the minimal apical localization sequence of baz are present at the C-terminal end of the T48 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).