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). (Generated by P1cre-mediated excision of the lexAop regulatory sequences present in vkg^{lexAop.UAS.GrabFP.ECM.mCherry}).