Its binding sites for many different proteins make it a hub that integrates several lines of upstream information. Once that happens, actin filaments grow, align themselves perpendicularly to the membrane, and push into it. In this way, they gradually generate one of the cell's finger-like spikes, a process much like sticking a finger out from inside a balloon, Cantley says. The comet tails generated in vitro by lab-made lipids may simulate that. And on the hypothetical fibroblast, the spikes represent the first stirrings towards moving into the wound.
Many questions remain, however.
The Kirschner paper only presents a pathway that can nucleate actin in vitro. It does not capture the myriad variations that will be found in different cell types in vivo, or even prove that this ever occurs in a living cell. Rong Li's study is the only one of the current set to have tested this pathway in vivo. Symptoms of WAS include bleeding, immune deficiency, eczema, inflammatory bowel disease, and lymphomas. Considered independent at first, they now appear linked through a flaw in controlling a cell's inner skeleton.