Fig. 3. Expression of EGFP-Myo1b and cytochalasin D affect the distribution and morphology of endosomes. (A) Ultra-thin section of Epon-embedded EGFP-Myo1b cells. Notice the clustered vacuolar endosomes with an electron-dense coat (stars). Ultra-thin cryosections of EGFP-Myo1b cells singly immunogold-labelled for EEA1 (B) or doubly immunogold-labelled for EEA1 and EGFP (C). Notice the numerous vesicular and tubular extensions at the opposite site of the coats in B and C (large arrows). (D) EGFP-Myo1b was visualized on whole-mounted cells. An endosome filled with HRP and immunogold-labelled for GFP is shown. Labelling is observed on the vacuolar domain and mostly concentrated in an extending tubule (arrows). (E) Ultra-thin cryosections of nontransfected cells immunogold-labelled for actin. Actin (long arrows) is detected on small tubulovesicular elements close to the endosomal vacuoles (stars) at the opposite site of the coated areas (short arrows). (F) Ultra-thin cryosection of MNT-1 cells immunogold-labelled for actin and treated with 0.4 µM cytochalasin D for 90 minutes. Actin is detected at the cytosolic side of tubular structures (arrows). Bars, 200 nm.