The airway epithelium of <i>Drosophila</i> larvae is characterized by different expression domains.

<p>The larval airway system is composed of interconnected tubes organized in a hierarchic structure (adapted after <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0102534#pone.0102534-Ruehle1" target="_blank">[6]</a>, A). Dorsal trunks are connected to the outside world and primary branches originate from them. The blind endings of the tracheal system are made from terminal branches (A). Different promoter Gal4 lines direct expression into different parts of the tracheal system. Driver lines such as <i>ppk4</i>-Gal4 label the entire airway system (B). In contrast, <i>c929</i>-Gal4 is specific for structures in the dorsal trunks (C), <i>ppk10</i>-Gal4 is surprisingly specific for primary branches (D) and <i>DSRF</i>-Gal4 labels exclusively terminal cells (E fluorescent channel, F transmitted light). Scale bars in B, C, D is 50 µm, in E, F 20 µm.