Clathrin starts off alone

A detailed visualization of clathrin dynamics by Marcelo Ehrlich, Tomas Kirchhausen (Harvard Medical School, Boston, MA), and colleagues reveals that two events—the initiation of clathrin-mediated endocytosis and recognition of cargo—are distinct. It appears that clathrin-coated pits start to form randomly but collapse unless stabilized, perhaps by cargo capture.

The Boston team marked clathrin and the AP-2 adaptor using fusions that allowed dynamic behavior, and collected complete datasets that were quantified automatically. The intensity of clathrin spots grew over time, with most reaching a critical point at ∼20 s. By then the curvature of the clathrin triskelions may become unsupportable without bolstering by other proteins. If labeled cargo joined the spots by then or soon after then, the spot continued to grow; but otherwise the spot dissipated without the burst of dynamin accumulation characteristic...