Ultrastructure of the ARSs labeled with gold-conjugated anti-GFP. (A–D) Cross sections of nerve cords dissected from third instar larvae carrying moesin-GFP in the SPG cells and processed either by chemical fixation (A) or by HPF followed by freeze substitution (B–D). The perineurial (PN) and subperineurial (SPG) cells (two neighboring SPG cells are marked by yellow or by pink), septate junctions (S.J.), and neurons (N) are indicated in A and B. The nerve cords shown in B–D were labeled with anti-GFP antibody and secondary 10-nm gold–conjugated antibody to visualize moesin-GFP. Low magnification (similar to that in A) of the nerve cord is shown in B, and the two corresponding regions marked in B are shown in higher similar magnification in C and D. The immunogold labeling in C (arrows) is detected very close to the membrane indentation that corresponds to the ARSs. No GFP labeling was detected at the nearby septate junction shown in D (arrow).