Résumé
The secretion of the morphogen Sonic Hedgehog (SHH) plays a vital role in embryonic brain development in vertebrates. Numerous studies have demonstrated that SHH acts on target cells at a distance from SHH-producing cells via transport in extracellular vesicles (EVs). Previously published work from our lab demonstrated that SHH is packaged and secreted in a distinct subtype of EVs known as ART-EVs due to their unique protein signature of AXL, Rab18 and TMED10. However, the molecular mechanisms that govern the intracellular transport of SHH and its subsequent secretion in ART-EVs is still poorly understood. Here, we employed the retention using selective hooks (RUSH) system to show that newly-synthesized SHH is trafficked through the classical biosynthetic secretory pathway, using TMED10 as an ER cargo receptor for efficient ER-to-Golgi transport. Moreover, silencing of TMED10 leads to a decreased trafficking of SHH to the cell surface, while neosynthesized transferrin receptor (TfR) transport was independent of TMED10. As a consequence, we observed decreased SHH levels in small EVs (sEV) secreted by TMED10-depleted cells and subsequent reduced SHH signalling activity on receiving cells. Finally, we utilized the Drosophila wing imaginal disc model to demonstrate that the homologue of TMED10, Baiser, participates in Hedgehog (Hh) secretion and signalling in vivo. In conclusion, our work highlights the role of TMED10 in cargo-specific egress from the ER and sheds light on a novel important partner of neosynthesized SHH secretion.