By 1970, several ultrastructural studies reported that different cell types contained thin filaments, 50 Å in diameter, which resembled the actin filaments seen in muscle cells. Similar filaments were also observed in the growing tips of axons, where they formed a network or mesh along the periphery. By analogy, most scientists assumed these actin-like filaments would also be involved in contraction and promote cellular movement. A series of papers published by Norman Wessells and his group at Stanford University (Yamada et al., 1970; Yamada et al., 1971; Spooner et al., 1971) provided the necessary correlative link: only when there was filament structure was there also motile function.
The studies were made possible by a new pharmacological tool. Cytochalasin B had been shown to inhibit motility (Carter, 1967), but without any real idea of mechanism. Schroeder (1969) then demonstrated that the drug also inhibited cytokinesis—a process...
