Figure 2.

Diagram of canal section, showing subcellular morphology of lumen and canal tip. The apical membrane is shown in red surrounding the central lumen (in white), while the basal membrane is shown in grey. The apical surface is coated by actin filaments (thick red) and intermediate filaments (thick yellow) that together form the terminal web. Filaments extend to the distal terminus of the canal, presumably to help in canal extension. Small canalicular vesicles appear as separate vesicles (in blue) or connected to the lumen (in red) to form canaliculi. These vesicles are coated with vacuolar ATPase (VHA, black spikes on vesicles). Microtubules (cyan) extend along the length of the canal, interspersed with and outside the canaliculi. Some microtubules appear helically wound around the lumen. Early endosomes (EE) and recycling endosomes (RE) move along the canal length (See Supplementary Video S1). Gap junctions (black) connect the canal cytoplasm to neighboring hypoderm.