Figure 4.

HttQ13Q-induced synaptic overgrowth requires BMP signaling. A, Representative images of HttQ138-dependent synaptic overgrowth in genetic backgrounds altering BMP and JNK signaling. Elav^C155;UAS-HttQ138-mRFP caused severe synaptic overgrowth that was completely suppressed in Elav^C155;gbb¹/gbb²;UAS-HttQ138-mRFP and partially suppressed in Elav^C155;gbb¹/+;UAS-HttQ138-mRFP larvae. Expression of DN Bsk did not reduce HttQ138-induced overgrowth. Elav^C155/UAS-Bsk^DN;UAS-HttQ138-mRFP (female larvae) had overgrowth similar to Elav^C155;UAS-HttQ138-mRFP alone. Strong overgrowth was still observed when the levels of Wnd were reduced 50% reduced in Elav^C155;UAS-HttQ138-mRFP/wnd1 strains. B, Quantification of satellite bouton number in the indicated genotypes. Removal of Snx16 in Elav^C155;snx16^Δ1/ snx16^Δ2;UAS-HttQ138-mRFP rescues HttQ138-induced synaptic overgrowth. C, Synaptic HttQ138-mRFP levels detected in the indicated genetic backgrounds shown in B. D, Representative images showing pMad nuclear and NMJ immunostaining. Synaptic and nuclear pMad staining is lost in wit mutants (wit^A12/wit^B12, right panel), whereas synaptic pMad is elevated in HttQ138-expressing larvae. E, Quantification of pMad fluorescent labeling in nuclei of ventral nerve cord neurons. F, Quantification of pMad labeling at the NMJ. ANOVA followed by Tukey's multiple-comparisons test was used for statistical analysis. *p ≤ 0.05; **p ≤ 0.01; ***p ≤ 0.001. Error bars indicate SEM.