Figure 4.

Imp-L2 is necessary for blocking dInR signaling under starvation. (a,b) tGPH fluorescence (green, showing PIP₃ levels and thus indicating IIS activity) in the fat body of feeding third instar larvae under different nutritional conditions. Nuclear staining (Hoechst) is shown in blue in the right panels. (a) Under normal conditions ('yeast'), IIS activity is high in wild-type feeding third instar larvae. Upon starvation, only little PIP₃ localizes to the membranes of fat body cells. (b) In Imp-L2 mutants, IIS activity is higher than in control larvae and only slightly reduced after 4 h PBS starvation. (c) Survival of Imp-L2^Def42/Imp-L2^Def20early third instar larvae is severely compromised under starvation conditions. One copy of the genomic rescue construct (GR) suffices to restore viability. Heterozygous larvae were Imp-L2^Def42/+, control larvae y, w/w. Larvae (40) were subjected for 24 h to 20% glucose, 1% glucose or PBS. The experiment was repeated twice. (d) In starved larvae (y, w), Imp-L2 protein expression (green) is induced in fat body cells after 24 h PBS starvation. Imp-L2 is localized to vesicle-like structures but not detectable under normal nutritional conditions. Genotypes: (a,d) y, w; (b) y, w; Imp-L2^Def42/Imp-L2^Def20.