Abstract
Small GTPases of the Sar/Arf family are essential to generate transport containers that mediate communication between organelles of the secretory pathway. Guanine nucleotide exchange factor (GEFs) activate the small GTPases and help their anchorage in the membrane. Thus, GEFs in a way temporally and spatially control Sar1/Arf1 GTPase activation. We investigated the role of the ArfGEF GBF-1 in C. elegans oocytes and intestinal epithelial cells. GBF-1 localizes to the cis-Golgi and is part of the t-ER-Golgi elements. GBF-1 is required for secretion and Golgi integrity. In addition, gbf-1(RNAi) causes the ER reticular structure to become dispersed, without destroying ER exit sites (ERES) because the ERES protein SEC-16 was still localized in distinct punctae at t-ER-Golgi units. Moreover, GBF-1 plays a role in receptor-mediated endocytosis in oocytes, without affecting recycling pathways. We find that both the yolk receptor RME-2 and the recycling endosome-associated RAB-11 localize similarly in control and gbf-1(RNAi) oocytes. While RAB5-positive early endosomes appear to be less prominent and the RAB-5 levels are reduced by gbf-1(RNAi) in the intestine, RAB-7-positive late endosomes were more abundant and formed aggregates and tubular structures. Our data suggest a role for GBF-1 in ER structure and endosomal traffic.
Highlights
Intracellular communication between organelles along the secretory pathway is maintained by transport vesicles that bud off from the donor compartment and fuse with the target compartment
Since the null mutant in gbf-1 is lethal (National Bioresource Project Japan), we studied the function of GBF-1 in C. elegans by using RNAi
Hatched larvae frequently showed severe abnormalities in their cuticle formation (Fig. 1B). These cuticle defects that lead to rupture of bursting through the vulva were never observed in agef-1(RNAi) worms; AGEF-1 is the homologue of yeast Sec7 [3]
Summary
Intracellular communication between organelles along the secretory pathway is maintained by transport vesicles that bud off from the donor compartment and fuse with the target compartment. The ArfGEFs Gea and Gea in yeast have been shown to perform overlapping functions in the activation of Arf for retrograde transport from the Golgi to the ER, and they presumably act in intra-Golgi transport [4,5,6]. Their mammalian counterpart GBF1 is localized to the Golgi apparatus and has been shown to be essential for maintaining Golgi structure and traffic through the Golgi [5,7,8,9,10,11]
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