SNARE Sec22Mediates Membrane Trafficking In Drosophila

Backgrounds In eukaryotes, membrane trafficking maintains the endomembrane system and delivers proteins to their destinations in a highly regulated manner. During trafficking, specific membrane fusion is generally achieved by SNARE complex. Functional impairments of SNARE complex assemble are associated with diseases, such as immunodeficiencies. We isolated a SNARE protein Sec22mutation in a EMS screen designed to isolate genes whose loss causes trafficking defects in Drosophila. We further investigated the function of Sec22in membrane trafficking and its mechanism.Methods First, using the FLP/FRT system, we created animals with homozygous mutant clones in the fat body. The trafficking defects were monitored in vivo by examining the intracellular localization of GFP labeled organelle marker proteins. To assess the morphology of photoreceptors and vesicles, we performed transmission electron microscopy (TEM) analysis of the eyes of newly enclosed flies. Third, the interaction between Eyc and Sec22, Syx5and Sec22were detected by immune coprecipitation to analyze the mechanism of Sec22affecting membrane traffic.Results (1)We identified Sec22mutants that have membrane trafficking defects. Homozygous animals died during embryonic period.(2) KDEL-GFP(ER), Rab7-GFP (late endosome), LAMP-GFP (lysosome) were accumulated in Sec22homozygous mutant clones. Golgi (MANII-GFP) were accumulated in some clones. However some other clones showed reduction in MANII-GFP.(3) TEM results showed the eyes overall morphology is severely affected so that rhabdomeres can hardly be identified. In addition, there is a massive endoplasmic reticulum and lipid accumulation in Sec22mutant clones. Similar phenotypes were observed in Syntaxin5RNAi as well as overexpression of Eyc (eyes closed).(4) Sec22co-immunoprecipitated with Syx5and Eyc respectively.Conclusions Taken together,(1)Sec22, a Drosophila SNARE protein, mediates traffic between ER and Golgi, which is essential for growth and development;(2) Syx5, Eyc and Sec22may coordinate to mediate membrane fusion in Drosophila. Our research firstly offers available phenotypic data in Drosophila.