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. Author manuscript; available in PMC: 2011 Oct 1.
Published in final edited form as: Curr Opin Cell Biol. 2010 Aug 23;22(5):633–639. doi: 10.1016/j.ceb.2010.07.016

Figure 3. Regulation of tube diameter and length.

Figure 3

The COP I/II secretion apparatus (light blue) is required for a burst of apical secretion (apically secreted proteins–dark blue; chitin–grey) that correlates with inflation of the tube lumen (lumenal matrix –yellow). Later apical secretion of the chitin modifiers, Serp and Verm (red), is important in limiting the growth of the apical membrane (green) along the long axis of the dorsal trunk tube (eg. to regulate tube length). During tube expansion, chitin cable (grey lines) formation is essential for uniform diametric growth. Proteins localized to the septate junctions (SJ–magenta lines) provide an additional level of regulation on tube size by limiting the expansion of apical polarity proteins, and thus restricting expansion of the apical membrane domain.