(A–B) Effects of GrabFP-AExt expression on the localization of Dally-YFP (A) and PMCA-YFP (B). Optical cross-sections of target proteins alone (Ctrl., left) or co-expressed with GrabFP-AExt (middle). Quantification of target-protein levels (left) in the absence (black) or the presence of GrabFP-AExt (continuous red line). Corrected profiles are indicated by a dashed red line. (C–D) Localization of Dally-YFP (C) and Fra-YFP (D) in control conditions (left) and when co-expressed with GrabFP-BExt (middle), quantification is shown to the left. (E–F) Representative cross-sections (top) and quantification (bottom) of relative GrabFP-AExt (E) and GrabFP-BExt (F) localization when expressed alone (Ctrl.) or when co-expressed with YFP/GFP-tagged target protein. Target proteins of basolateral localization tend to mislocalize GrabFP-AExt (E) toward the junctional/basolateral compartment (see reduction in relative apical localization [brown]). In contrast, GrabFP-BExt (F) is more resistant to mislocalization by apically localizing target proteins and shows only slight increases in apical localization. Sample numbers for shown quantifications in A-F: GrabFP-AExt n = 4, +Dally n = 10, +NrxIV n = 6, +Dlp n = 8, +PMCA n = 5, GrabFP-BExt n = 4, +Dally n = 10, +Notch n = 8, +Fra n = 9, +Crb n = 9, +Ed n = 6. Statistical significance was assessed comparing control with corrected profiles using a two-sided Student’s t-test with unequal variance (*p<0.05).