Publisher Summary The knowledge of the structural organization of actin filaments in
protrusive organelles—lamellipodia and filopodia—is instrumental for understanding the
mechanisms of leading edge protrusion and of actin polymerization-based motility, in
general. This chapter reviews the contribution of electron microscopy (EM) to the progress in
this field. It focuses on the first step of the motility cycle—the extension of a pseudopod—and
the role of EM in understanding the mechanisms of pseudopodia protrusion. The chapter …