Figure 4. Sec bodies form at ERES but COPII- and COPI-coated vesicle formation is not required.
(A) Stills of a GFP-Sec23 time-lapse video of a cell incubated in KRB (t = 0) for 60 min showing Sec body formation. (B–B″) IF visualization of miniSec16-V5 (B, B′) and ΔNC2-3-Sec16-V5 (B, B″) in S2 cells incubated in Schneider's (B) and KRB for 4 hr. Endogenous Sec16 is in red. Note that the cup-shaped ER forms a cradle for Sec bodies (B′, insert). (C) IF visualization of Sec16 and GFP-Sec23 in mock and Sar1-depleted S2 cells grown in Schneider's and incubated in KRB for 4 hr. Note that the ERES are enlarged in Sar1-depleted cells (arrows) and Sec bodies form in both conditions to the same extent. (D) IF visualizations of Sec16 and Delta-myc in S2 cells incubated with brefeldin A (BFA) in Schneider's and KRB for 3 hr. Note that Delta transport is inhibited in both cases as Delta is retained intracellularly. (E) IF visualization of Sec16 in S2 cells grown in Schneider's and incubated in KRB for 4 hr in the presence or absence of brefeldin A (BFA). Note that pre-incubation with the drug does not affect Sec body formation during starvation. Scale bars: 10 μm.