Recycling endosomes attach to the trans-side of Golgi stacks in Drosophila and mammalian cells

Abstract

Historically, the trans-Golgi network (TGN) has been recognized as a sorting center of newly synthesized proteins, whereas recycling endosome (RE) is a compartment where endocytosed materials transit before being recycled to the plasma membrane. However, recent findings revealed that both the TGN and RE connect endocytosis and exocytosis, and thus are functionally overlapping. Here we report, in both Drosophila and microtubule-disrupted HeLa cells, that REs are interconvertible between two distinct states, namely Golgi-associated REs and free REs. Detachment and reattachment of REs and Golgi stacks were often observed. These two types of REs were in the route of Glycosylphosphatidylinositol-anchored cargo protein released from the endoplasmic reticulum, but not in that of Vesicular stomatitis virus G protein. In plants, it has been established that there are two types of TGNs: the Golgi-associated TGN and Golgi-independent TGN. Dynamics of REs in both Drosophila and mammalian cells revealed strong similarity to plant TGNs. Together with the molecular-level similarity, these results indicate that fly/mammalian REs are equivalent organelles to TGNs in plants, and evoke reconsideration of identities and functional relationships between REs and TGNs.