Figure 1.

The JNK signaling pathway is required for tumor cell invasiveness. The eyeless-FLP/MARCM system was used to induce GFP-marked clones (green) of the indicated genotypes. The left panels of (A, B) show epifluorescence images of eye/antennal/brain complexes. All other panels show confocal micrographs (projections of multiple sections or single confocal sections for magnification of VNC, respectively) of third instar larval brains on day 6 AEL. Brains were stained with phalloidin to visualize actin filaments. (A) ras^V12, scrib^−/− double mutant cells proliferate strongly and overgrow wild-type tissue in the brain lobes (bl) and the eye/antennal discs. The tumor cells display pronounced migratory behavior. At higher magnification (A, right panels), the elongated shape and the prominent actin cytoskeleton (phalloidin stain) in the clonal cells invading the VNC are visible. The tumor cell morphology differs strikingly from that of normal brain cells. (B) Blocking JNK signaling by Bsk^DN expression in ras^V12, scrib^−/− cells completely suppresses tumor cell invasiveness and the VNC is free of GFP-positive clonal cells. Scale bars=50 μm.