Dye-permeability and Endocytosis Assays

For dye-permeability assays, 10 kDa Dextran-TR (ThermoFisher Scientific) was injected into late-stage 16 embryos (after the formation and maturation of SJ) as described in ref. ^{64 (link)}. For endocytotic assays, we injected 10 kDa Dextran into the haemocoel of stage 13–14 embryos, as described^{3 (link)}. Dextran and drugs were injected laterally or posteriorly in embryos mounted on a coverslip with heptane/glue and covered with halocarbon oil (#700) (Sigma). LAT-B was diluted in 6% DMSO and 94% H₂O and different concentrations (0.5, 1, 2, 10, 50 mM) were injected, yielding approximately a dilution of 50-fold in the embryo^{65 (link)}. All drug injections were performed in late-stage 16 (15.5 h AEL) dechorionated embryos using a microinjection system (FemtoJet, Eppendorf) coupled to an inverted fluorescence microscope (Cell Observer, Zeiss).