Endocytosis of Wingless via a dynamin-independent pathway is necessary for signaling in Drosophila wing discs

Abstract

Endocytosis of ligand-receptor complexes regulates signal transduction during development. In particular, clathrin and dynamin-dependent endocytosis has been well studied in the context of patterning of the Drosophila wing disc, wherein apically secreted Wingless (Wg) encounters its receptor, DFrizzled2 (DFz2), resulting in a distinctive dorso-ventral pattern of signaling outputs. Here, we directly track the endocytosis of Wg and DFz2 in the wing disc and demonstrate that Wg is endocytosed from the apical surface devoid of DFz2 via a dynamin-independent CLIC/GEEC pathway, regulated by Arf1, Garz, and class I PI3K. Subsequently, Wg containing CLIC/GEEC endosomes fuse with DFz2-containing vesicles derived from the clathrin and dynamin-dependent endocytic pathway, which results in a low pH-dependent transfer of Wg to DFz2 within the merged and acidified endosome to initiate Wg signaling. The employment of two distinct endocytic pathways exemplifies a mechanism wherein cells in tissues leverage multiple endocytic pathways to spatially regulate signaling.clathrin and dynamin-independent endocytosis | Wingless signaling | pH of endosome | wing disc development | Garz localization

Ykt6 membrane-to-cytosol cycling regulates exosomal Wnt secretion

“…Within the polarized epithelium of Drosophila WID, apically presented and subsequently endocytosed Wg might serve as a signaling reservoir that can get rapidly mobilized by Ykt6-mediated secretion at the basolateral side. In lines with this idea is a recent study demonstrating that Wg is endocytosed apically, while its receptor Fz2 is internalized from the basolateral side of WID and both meet in acidified endosomes for signal transduction (Hemalatha et al, 2016). Moreover, Wg endocytosis from the apical side seems to depend on HSPGs, which are also involved in cargo sorting onto exosomes via Alix and syntenin (Ghossoub et al, 2014).…”

Drosophila VAMP7 regulates Wingless intracellular trafficking

“…There are two models describing how the apically secreted Wg encounters basolateral receptors at receiving cells. One suggests that Wg and receptors can be internalized separately, and then, endosome fusion results in Wg and receptor interaction in the receiving cells [ 51 ]. Another model proposes that apically secreted Wg undergoes endocytosis and will be transported to the basolateral surface in the producing cells [ 22 ], then spread to the receiving cells for the interaction with receptors.…”

GBF1 and Arf1 function in vesicular trafficking, lipid homoeostasis and organelle dynamics

“…GBF1 is the GEF responsible for activating Arf1 in a clathrin‐independent endocytosis pathway that requires both Arf1 and Cdc42, known as the clathrin‐independent carriers/GPI‐anchored protein enriched endosomal compartments (CLIC/GEEC) pathway (Gupta et al., ) (Figure ). This pathway has recently been implicated in patterning of the Drosophila wing during development through endocytosis of the morphogen Wingless (Hemalatha et al., ). In addition to the Drosophila orthologues of GBF1 and Arf1 (Garz and Arf 79F), Class I phosphatidylinositol 3‐kinase is also required for Wingless endocytosis, which interestingly occurs independently of the Wingless receptor DFrizzled2 (Hemalatha et al., ).…”

“…This pathway has recently been implicated in patterning of the Drosophila wing during development through endocytosis of the morphogen Wingless (Hemalatha et al., ). In addition to the Drosophila orthologues of GBF1 and Arf1 (Garz and Arf 79F), Class I phosphatidylinositol 3‐kinase is also required for Wingless endocytosis, which interestingly occurs independently of the Wingless receptor DFrizzled2 (Hemalatha et al., ). GBF1 is also required for chemotaxis of migrating neutrophils, where it activates Arf1 upon G‐protein coupled signalling triggered by ligands such as bacterial N ‐formyl peptides (Mazaki et al., ).…”