INTERACTIONS AMONG ENDOPLASMIC-RETICULUM, MICROTUBULES, AND RETROGRADE MOVEMENTS OF THE CELL-SURFACE

Relationships among the endoplasmic reticulum (ER), microtubules, and bead movements on the cell surface were investigated in the thin perip heral region of A6 cells, a frog kidney cell line. ER tubules were oft en aligned with microtubules, as shown by double-labeling with DiOC(6) (3) and anti-tubulin in fixed cells. In living cells stained with DiOC (6)(3) and observed in time lapse, there were frequent extensions, but few retractions, of ER tubules. In addition, there was a steady retro grade (towards the cell center) movement of all of the ER at similar t o 0.3 mu m/min. Since microtubules are often aligned with the ER, micr otubules must also be moving retrogradely. By simultaneous imaging, it was found that the ER moves retrogradely at the same rate as aminated latex beads on the cell surface. This indicates that the mechanisms f or ER and bead movement are closely related. Cytochalasin B stopped be ad and ER movement in most of the cells, providing evidence that actin is involved in both retrograde movements. The ER retracted towards th e cell center in nocodazole while both ER and microtubules retracted i n taxol. Time lapse observations showed that for both drugs, the retra ction of the ER is the result of retrograde movement in the absence of new ER extensions. Presumably, ER extensions do not occur in nocodazo le because of the absence of microtubules, and do not occur in,taxol b ecause taxol-stabilized microtubules move retrogradely and there is no polymerization of new microtubule tracks for ER elongation. (C) 1994 Wiley-Liss, Inc.