Fig. 2. Characterization of BG2 cells. (A) Morphology of cell population (phase contrast). Cells display polarized lamella. (B) Protrusive activity (time-lapse sequence). Leading edge moves forward by combination of filopodial (arrowheads) and lamellipodial protrusion. Dotted line shows the initial position of the cell edge. Time in min:sec. (C) Actin cytoskeleton (phalloidin staining). Leading edge contains diffuse network in lamellipodia and distinct bundles in filopodia and microspikes; stress fibers are present in the cell interior. (D) Structural organization of lamellipodia (EM). Actin filaments form dendritic network in lamellipodia and bundles of long filaments in filopodia. Circled region is enlarged in the inset to show actin bundle. Bars, 10 µm (A), 5 µm (B,C) and 1 µm (D).