lexAop and UAS regulatory sequences and a minimal Hsp70 promoter (derived from the pUASTLOTattB vector) are fused upstream of a fusion protein that encodes a nanobody-based GFP trap that localizes to the extracellular matrix of the basal lamina. The fusion protein contains the vkg coding sequence with a mCherry fluorescent tag and the GFP-binding VHH(GFP4) nanobody inserted between the first and second exon (the two inserted tags are separated by a short linker sequence). 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).