Fig. 7

Canaliculi formation at pupal stage P5 proceeds from the ductule end. Entire glands were fixed, labeled with phalloidin (green) and DAPI (blue), and imaged by confocal serial sectioning. a and a’ In the secretory cell outlined by a dashed yellow line (a’), an array of F-actin defines a short tube that originates at the distal ductule end (broad arrow) and terminates blindly in the cytoplasm (arrowhead). Continuity between the F-actin tube and ductule was backtraced in confocal serial sections, although only one optical plane is shown here. b-f Five optical planes (inter-plane distance 1.15 μm) through a P5 acinus. A continuous blind-ending (arrowhead) tube is outlined by phalloidin staining and takes a convoluted path around the nucleus (asterisks) of the prospective secretory cell. Tube segments in each section plane are indicated by red lines and summarized in e. Spheroidal structures (thin arrows) close to the tube are also delineated by phalloidin staining. The F-actin tube is connected to the ductule (broad arrow); the latter is indicated by a dashed white line (e,f). Bars, 5 μm