Figure 1: Airway clearance in Drosophila embryos Confocal images (A-C) show whole mount (A) and magnifications of the trachea (B,C) at stage 16 and stage 17 embryos. For detecting tracheal tube lumina the fluorescein conjugated chitin-binding-probe (Cbp) was used. Cbp recognizes chitin. (A) Three-dimensional projection of confocal Z-stacks across the tracheal system visualizes chitinous tracheal tubes. The main airways are indicated as dorsal trunk (dt), dorsal branches (db), lateral branches (lb). (B) In stage 16 embryos single confocal sections show that chitin is localized in a transient luminal cylinder-like matrix (arrowheads), which controls tube expansion. (C) At the end of embryogenesis, at stage 17, airway lumina (arrowhead) are cleared from the chitin cylinder. Scale bars represent 10 μm. (D-F) At stage 17, embryos undergo airway liquid-clearance and air-filling. This process can be detected due to different light diffractions by bright-field microscopy. Red dashes indicate air-filled airways, blue dashes liquid-filled lumina. The air-filling process starts in the mid of one dorsal trunk (D), expands along the main airway including also the other hemisphere (E, white arrowhead) until all airways are aerated (F). Red arrowheads point to small dorsal and lateral tracheal tubes. All images show anterior to the left and dorsal to the top.