Figure 4.

Modulation of the JNK Signaling Pathway in Aβ42-Expressing Clones Dictates the Survival or Elimination of WT Cells

(A) Control clones show a regular pattern of pJNK staining throughout the eye disc. This pattern is consistent across WT GFP-positive and WT GFP-negative clones. Scale bars, 50 μm.

(B) Eye disc with GFP-positive clones expressing Aβ42. pJNK levels are increased in Aβ42-expressing clones. Magnification shows increased pJNK signal overlapping with the Aβ42-expressing clone. The upregulation of pJNK expression in Aβ42-expressing clones extends into WT sister clones. Scale bars, 50 μm.

(C) pJNK levels were compared for control sister clones and Aβ42-expressing and WT sister clones. No significant difference was observed between control clones (N = 17, p = 0.72, two-way unpaired Student's t test). Data are presented as mean ± SEM. We observed an increase in pJNK mean gray value in Aβ42-expressing clones (N = 17, ∗p < 0.05, two-way unpaired Student's t test). Because pJNK staining results in strong signal in the optic stalk, for pJNK mean gray value calculation, we selected for analysis the region of the z stack that did not substantially overlap with the optic stalk staining.

(D) To test the effects of upregulating JNK signaling, we expressed hep^Act in Aβ42-expressing cells. Expression of hep^Act in clones led to a non-autonomous increase in cell death throughout the entire eye, resulting in highly reduced eyes. Expression of hep^Act in all retinal neurons using GMR-Gal4 (GMR > hep^Act) triggers neurodegeneration. WT sister clones are highly reduced in size compared with clones expressing Aβ42 and hep^Act. Staining for pJNK revealed a region of increased pJNK levels overlapping with the area of the GFP-positive clone.

(E) GFP-positive clones expressing Aβ42 and hep^Act and GFP-negative WT clone sizes were quantified. WT sister clones are significantly reduced in size compared with clones expressing Aβ42 and hep^Act (N = 19, ∗∗p < 0.01, two-tailed unpaired Student's t test). Data are presented as mean ± SEM.

(F) To test the effects of downregulating JNK activity, we expressed bsk^DN in Aβ42-expressing neurons. Adult flies expressing bsk^DN in Aβ42-expressing neuronal clones show approximately WT eye size. Expression of bsk^DN in all retinal neurons using GMR-Gal4 (GMR > bsk^DN) results in eyes that are normal in appearance (ywhsflp/bsk^DN; Aβ42/+; FRT82BTubGal80/FRT82ubi-GFP). Expression of bsk^DN in Aβ42-expressing cells rescues the size of WT clones. Staining retinal neurons with Elav shows irregular spacing in the Aβ42-expressing clone but normal spacing in the WT clone.

(G) Areas of GFP-positive clones expressing Aβ42 and bsk^DN were compared with GFP-negative WT sister clones, showing no significant difference in size (N = 13, p = 0.58, two-tailed unpaired Student's t test).

Data are presented as mean ± SEM. See also Figures S1 and S2 and Table S1.