Fusion at the front

Neurite extension is dependent on the growing neurite's ability to get longer rather than fatter. Sakisaka et al. (page 17) now show that a protein called tomosyn works in a complex to help focus membrane growth to the tip of growing neurites.

As neurites grow, traveling vesicles are prevented from fusing willy-nilly to the plasma membrane first by their attachment to microtubule highways. Where those highways terminate—at the back of the growth cone—is where tomosyn takes over as a fusion inhibitor. With fusion prevented, the vesicles find their way to the actin cytoskeleton, which distributes them to the leading edge of the growth cone.

Sakisaka et al. found that, in growing neurites, tomosyn localizes at the rear of the growth cone. This area...