TheDrosophilaSec7 domain guanine nucleotide exchange factor protein Gartenzwerg localizes at the cis-Golgi and is essential for epithelial tube expansion

Abstract

SummaryProtein trafficking through the secretory pathway plays a key role in epithelial organ development and function. The expansion of tracheal tubes in Drosophila depends on trafficking of coatomer protein complex I (COPI)-coated vesicles between the Golgi complex and the endoplasmic reticulum (ER). However, it is not clear how this pathway is regulated. Here we describe an essential function of the Sec7 domain guanine nucleotide exchange factor (GEF) gartenzwerg (garz) in epithelial tube morphogenesis and protein secretion. garz is essential for the recruitment of COPI components and for normal Golgi organization. A GFP-Garz fusion protein is distributed in the cytoplasm and accumulates at the cis-Golgi. Localization to the Golgi requires the C-terminal part of Garz. Conversely, blocking the GDP-GTP nucleotide exchange reaction leads to constitutive Golgi localization, suggesting that Garz cycles in a GEF-activitydependent manner between cytoplasmic and Golgi-membrane-localized pools. The related human ARF-GEF protein GBF1 can substitute for garz function in Drosophila tracheal cells, indicating that the relevant functions of these proteins are conserved. We show that garz interacts genetically with the ARF1 homolog ARF79F and with the ARF1-GAP homolog Gap69C, thus placing garz in a regulatory circuit that controls COPI trafficking in Drosophila. Interestingly, overexpression of garz causes accumulation of secreted proteins in the ER, suggesting that excessive garz activity leads to increased retrograde trafficking. Thus, garz might regulate epithelial tube morphogenesis and secretion by controlling the rate of trafficking of COPI vesicles.

The clathrin adaptor AP-1 complex and Arf1 regulate planar cell polarity in vivo

“…42), and, for example, in flies, at the cis-Golgi, Arf1 together with its guanine nucleotide exchange factor/GEF Gartenzwerg regulate COPI retrograde transport 52 . We thus also tried to test this possibility.…”

Shaping of biological tubes by mechanical interaction of cell and extracellular matrix

“…The deposition of chitin, the major component of aECM and other matrix proteins in the luminal space, is associated with the onset of diametric expansion [10][11][12]. The secretion process is associated with materials present in the tracheal cell cytoplasm that are released as a bolus into the lumen, via COP I-mediated and COP II-mediated vesicle trafficking between the endoplasmic reticulum (ER) and Golgi apparatus [13][14][15][16][17][18][19], and the Diaphanous-dependent secretory pathway [20]. These general secretory pathways are required for deposition of aECM components and the addition of membranes into the apical surface, which expands the luminal space.…”

Regulating the large Sec7 ARF guanine nucleotide exchange factors: the when, where and how of activation

“…The effects of deletions of HDS1 may be restricted to Sec7p as they are not observed in the yeast Gea1p (a GBF1 ortholog) [63]. However, a C-terminal truncation (amino acids 982–1983) of Drosophila Garz (a GBF1 ortholog) decreases targeting to the Golgi [64], as does deletion of the C-terminus (removal of amino acids 1060–1859) in GBF1 (E.S., unpublished data). The extreme C-terminus (amino acids 1762–1859) of mammalian GBF1 is dispensable for membrane recruitment [44].…”

“…Such assemblies likely include GAPs and other effectors in addition to the initiator (cargo), GEFs and GTPases. For example, recent findings show that cargo sorting/packaging machinery exemplified by ARF-GAPs might also affect GEF function: the Drosophila ortholog of GBF1, Garz, has been shown to interact genetically with the ARF1 ortholog ARF79F and with the ARF1-GAP ortholog Gap69C [64]. Whether this interaction is conserved in other species and whether the ARF GAP influences the positioning and/or activity of the GEF is unknown.…”