Figure 6.

Axonal varicosities are found within the segmental nerve of the fmi mutant

(A, B). Representative images of colocalization of the microtubule-associated protein Futsch (22C10, green) and the endocytotic protein DAP160 (red) on segmental nerves of control larvae (A) and fmi^E59/Df mutant larvae (B), respectively. Note that DAP160 is present at low levels uniformly along the control segmental nerve. In contrast, some segmental nerves similar to the one shown in panels (B) have a string of bouton-like varicosities clustered on axons. Insets show one of the axonal varicosities at higher magnification.

(C-F). Representative images showing colocalization of various synaptic (Hiw, nc82) and synaptic vesicle proteins (CSP, n-Syb, Syt I, VGluT) along segmental nerves of the fmi mutant larvae. Panels (C) show that the synaptic vesicle protein cysteine-string protein (CSP, green) colocalizes with the synaptic vesicle protein neuronal synaptobrevin (n-Syb, red) within the string of bouton-like varicosities along the segmental nerve. Panels (D) show that the peri-active zone protein Highwire (Hiw, green) colocalizes with the synaptic vesicle protein synaptotagmin I (Syt I, red) within the bouton-like varicosities. Panels (E) show that the active zone marker nc82 is clustered in bouton-like shapes along the segmental nerve (marked by HRP). Panels (F) show the localization of the Drosophila vesicular glutamate transporter (VGluT) along the segmental nerve (marked by HRP).

(G & H). The axonal varicosities found in the fmi^E9/fmi⁷² mutant (G) can be rescued by neuronal expression of the wild type Flamingo in the mutant background (F). Note the absence of Syt I-positive varicosities along the segmental nerve in the rescued fmi mutant. Arrowheads point to synaptic boutons normally found on bodywall muscles. However, this rescue is statistically significant but not a full rescue (see Fig. S3E).