Figure 4.

Fat body-produced Fon is required for stable muscle attachments. (A–D) Visualization of larval muscles (F-actin; green) after fon RNAi knockdown using the indicated Gal4 drivers. Driving fon RNAi under expression of the ubiquitous da (A) or the fat body driver ppl (D) regulatory sequences results in muscle attachment defects (carets). Knockdown of fon RNAi in the muscle (24B-Gal4) occasionally results in missing muscles (B, bracket), while knockdown in tendon cells [C; stripe (sr)-Gal4] does not alter muscle attachment stability. (E) Percent muscle detachment in the indicated genotypes. Muscles within each fillet were scored as being detached or intact (n ≥ 19 for each genotype). (F) qPCR reveals that fon mRNA levels are decreased upon fon RNAi knockdown (da > fon RNAi) compared to control (da-Gal4) L3 larvae. (G–H′) βPS integrin (red) and DAPI (blue) label fat body tissue from ppl > fon-GFP L3 larvae fed control DMSO or BFA. BFA treatment blocks efficient Fon–GFP (green) transport out of fat body cells. (I) Quantitation of mean fluorescence intensity within individual fat body cells (n = 12 for each untreated and BFA-treated samples). Mean ± SD; P-values: **** P < 0.001, *** P < 0.005. Bars, 200 µm for A–D; 50 µm for F and G.