The Drosophila melanogaster trachea is a branched network of rigid chitin-lined tubes that ramify throughout the body and functions as the fly’s respiratory organ. Small openings at the ends of the tracheal tubes allow gas exchange to occur by diffusion between internal tissues and the exterior environment. Tracheal tubes are lined by a single layer of epithelial cells, which secrete chitin and control tube morphology and size. Studies of tracheal development in Drosophila embryos have elucidated fundamental mechanisms of tube morphogenesis and maintenance in vivo, and identified major signaling pathways that regulate these processes (Manning and Krasnow, 1993; Affolter and Shilo, 2000; Zuo et al., 2013; Kerman et al., 2006; Schottenfeld et al., 2010). In recent years, there has been growing interest in the trachea during metamorphosis, when tracheal branches that had served as the respiratory organ in the larva decays and is repaired or replaced by new tracheal tissue arising from committed tracheal progenitor cells, or mature tracheal cells de-differentiated to a progenitor state (Manning and Krasnow, 1993; Sato and Kornberg, 2002; Guha et al., 2008; Guha, and Kornberg, 2005; Weaver and Krasnow, 2008; Pitsouli and Perrimon, 2010; Chen and Krasnow, 2014) forming the adult tracheal by the end of the process. The ongoing decay and tissue formation models aspects of tissue repair and regeneration in other organisms, and has been used to understand how progenitor cells divide and differentiate (Pitsouli and Perrimon, 2010; Pitsouli and Perrimon, 2013), and how they grow out of their niche to replace decaying tissue (Chen and Krasnow, 2014). Here, we present a protocol to dissect, fix, and immunostain tracheal tissue in Drosophila larvae and pupae undergoing metamorphosis. This protocol can be used to immunostain proteins expressed in tracheal tissue, or to amplify signals from weakly expressed fluorescent reporters (as shown in Figure 6). With the appropriate antibodies and genetic reporters, this protocol can be used to visualize decaying larval trachea and the progenitor cells that replace them in a time-course analysis, as well as determine expression of proteins in these cells that may play a role in tissue decay and replacement.
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