αArp2 inhibits filopodia and lamellipodia formation during spreading on glass.

Platelets were either directly spread on glass in plasma or were permeabilized briefly first with or without antibodies, and then mounted on glass. After 20 minutes, adherent platelets were fixed in the presence of FITC–phalloidin to stabilize and stain the F-actin. Top row of micrographs shows representative examples of spread platelets under 3 control conditions: no treatment (No Tx), permeabilized (+Tx), and permeabilized and loaded with preimmune antibodies (+Tx/+pre). The lower row of micrographs shows representative examples of platelets permeabilized and loaded with αArp2 before exposure to glass (+αArp2). Typical effects are frozen at the rounded stage (left panel), abnormal lamellipodia (middle panel), and blebbing (right panel).