Fig. 4. Ectopic Pax3 expression in Saos-2 cells induces directed cell protrusive behavior. F-Actin staining of Ad-ß-gal control infected (A, top panel) or Ad-Pax3^flag-infected cells (A, bottom panel) at 72 hours postinfection illustrates the presence of multiple stable lamellipodia and filopodia-like protrusions in Ad-Pax3^flag-infected cells. The episodic nature of these protrusions is illustrated by the retraction of a lamelliform protrusion (arrowhead) in sequential stills (D-G) from a time-lapse recording of Pax3-infected cells. Pax3-induced cell protrusions were often elaborate, resembling growth cones (B). Stable filopodia-like protrusions from individual cells were frequently observed to be directed at neighboring cells (C and arrow in E). Time-lapse analysis revealed that these protrusions were involved in cell behavior that resulted in fusion of aggregates (D-G) and in recruitment of free cells to aggregates (H-J) (see text for details). Note cell extending from aggregate to neighboring cell (arrow in H). Bars, 20 µm (A); 40 µm (B,C); 50 µm (D); 80 µm (H).