The dimensions and shapes of epithelial tubules in animal organs are precisely controlled to ensure normal organ function. Recent work in various model systems has highlighted the importance of protein trafficking through the secretory pathway during the morphogenesis of epithelial systems. The expansion of the tracheal tubules in Drosophila,for example, has been shown to depend on the trafficking of coatomer protein complex I (COPI)-coated vesicles between the Golgi complex and the endoplasmic reticulum (ER). But how is this pathway regulated? On page , Kristina Armbruster and Stefan Luschnig report that the Sec7 domain guanine nucleotide exchange factor protein Gartenzwerg (Garz) has an essential role in epithelial tube morphogenesis and protein secretion in Drosophila. They show that garz is required for the morphogenesis of tubular epithelia during embryogenesis, for normal Golgi morphology, and for the localisation of COPI components. Garz localises to the cis-Golgi complex. Moreover, genetic interaction experiments place garz in a regulatory circuit that controls COPI trafficking, and overexpression of garz causes accumulation of secreted proteins in the ER. On the basis of their results, the authors suggest that Garz regulates epithelial tube morphogenesis in Drosophila by controlling the trafficking rate of COPI vesicles.
