Figure 2.

Fon is required for muscle attachment stability and larval locomotion. (A–I′) Internal views of larval fillets at low (A–C) or high magnification (D–I′) in WT or fon mutant larvae in XY (A–F′) or XZ (G–I′) focal planes. (A) WT larval muscles are rectangular when firmly attached to other muscles or tendon cells. (B and C) Deletion of the fon locus (fon^Δ24/Df; B) or an insertion that disrupts fon (fon^MB/fon^MB; C) results in many detached muscles (carets). (D–I′) Phalloidin (red) and βPS integrin (green) staining in the indicated genotypes. (D and G) WT dorsal oblique muscle 10 (DO2) shows accumulation of βPS integrin at attachment sites between adjacent muscles (white arrowhead). (E, F, H, and I) fon mutant DO2 muscles reveal large gaps between adjacent hemisegments, yet retain βPS integrin accumulation at muscle edges (white arrowheads). (J) Analysis of different fon mutant alleles show an increased percentage of detached myofibers. (K) The dorsal oblique muscles 9 and 10 (DO1 and 2) exhibit a variable, but significant increase in gap distance between adjacent hemisegments in fon mutants. (L) L3 wandering larvae (29 ≤ n ≤ 46 for each genotype) with mutations in the fon locus traverse across agar plates at a velocity lower than their WT counterparts, but similar to Tig mutants. Mean ± SD; P-values: *** P < 0.005. Bars, 200 µm for A–C; 50 µm for D–I′.