ER exit sites inDrosophiladisplay abundant ER-Golgi vesicles and pearled tubes but no megacarriers

Abstract

Secretory cargos are collected at ER exit sites (ERES) before transport to the Golgi apparatus. Decades of research have provided many details of the molecular events underlying ER-Golgi exchanges. Essential questions, however, remain about the organization of the ER-Golgi interface in cells and the type of membrane structures mediating traffic from ERES. To investigate these, we used transgenic tagging in Drosophila flies, 3D-SIM and FIB-SEM to characterize ERES-Golgi units in collagen-producing fat body, imaginal discs and imaginal discs overexpressing ERES determinant Tango1. We found in front of ERES a pre-cis-Golgi region involved in both anterograde and retrograde transport. This pre-cis-Golgi is continuous with the rest of the Golgi, not a separate intermediate compartment or collection of large carriers, for which we found no evidence. We found, however, many vesicles, as well as pearled tubules connecting ERES and Golgi.

TANGO1 marshals the early secretory pathway for cargo export

“…A key difference between the yeast and metazoan early secretory pathways is the presence of an anastomosis of membranes that appear tethered at metazoan ERES, physically contiguous with the ER, but maintained as a distinct subcompartment [13,14,38]. To generate this interwoven, tubular network extending from ER, membranes need to be tethered at the ERES and held in place as they fuse with each other and interconnect.…”