MAG cross-linking leads to a transient depolymerization of actin without major morphological alterations in OLs. OLs in culture were either left untreated (A,D,F) as controls or treated with anti-MAG mAb (1:100, 15 minutes at 37°C) followed by anti-mouse IgG (1:500, 15 minutes at 37°C) (B,C,E,G). In some cases (C), the antibody-containing medium was washed and cells were incubated with fresh medium for an additional 14 hours. Cells were then immunostained (see Methods) with phalloidin (A–C), O4 (D,E) and anti-tubulin (F,G) antibodies for epifluorescence microscopy. Scale bars: 5 μm.