The GFP–COL transport to the Golgi via a “short-loop” pathway. (A) Immunofluorescence image of a primary skin fibroblast labeled for (1) endogenous COL1A1 (green) and Sec31A (red) and (2) endogenous COL1A1 (green) and GM130 (red), both after 30-min incubation in presence with 50 µg·ml⁻¹ ascorbate. Scale bars, 10 µm; in enlargements, 1 µm. (B) Schematic of a cell with zoomed in region showing COL1A1 transport from ERERS in close proximity to the Golgi. (1) COPII-dependent packaging of procollagen into nascent buds. (2) These buds are expanded by TANGO1-dependent fusion with the ERGIC. (3) Carrier expansion encapsulates procollagen. Questions remain as to the extent of expansion required and the flexibility of the trimer at this stage. (4) Scission of the carrier generates a compartment that almost immediately adopts the identity of the ERGIC and progresses to become the first cisterna of the Golgi. In this model, the ERGIC acts as an intermediate to both expand the nascent ER-derived carrier and to ensure compartmentalization of ER and Golgi.