Host-pathogen interactions in Drosophila PERSPECTIVE and an internal component comprising the gut (or endoderm). The formation of both the outer epithelial barrier and the inner intestinal barrier depends on the formation and maintenance of intercellular junctions, and many basic discoveries in this field have been made in Drosophila (Banerjee et al., 2006; Furuse and Tsukita, 2006; Wirtz-Peitz and Zallen, 2009 ). Such studies have delineated key mechanisms involved in establishing apical-basal polarity, including the assembly of distinct protein complexes at adherens junctions and septate junctions (claudin-dependent junctions that share important similarities with vertebrate tight junctions). One highly conserved feature of this process is the role of the exocyst protein complex in trafficking proteins such as cadherins and cell signaling components to adherens junctions (Andrews et al., 2002; Beronja et al., 2005; Blankenship et al., 2007; Jafar-Nejad et al., 2005; Langevin et al., 2005; Mehta et al., 2005; Murthy et al., 2003; Murthy et al., 2005; Murthy and Schwarz, 2004; Murthy et al., 2010) .