Elimination by shedding

Synapse elimination occurs via a combination of axon retraction and the shedding of vesicles dubbed “axosomes,” according to Derron Bishop, Thomas Misgeld, Jeff Lichtman (Harvard University, Cambridge, MA), and colleagues. The axosomes appear to end up inside glia, and may help carry both signals and essential functional materials to this supporting cell type.

Terrestrial vertebrates need synapse elimination because their nervous systems are not dedicated, hard-wired circuits but redundant. Overconnection in uncoordinated neonates gradually gives way, via synapse elimination, to single, point-to-point neural connections and fine motor control.

Lichtman's group got a new look at the process at the mouse neuromuscular junction by correlating light and serial electron microscopy (EM). The resolution of the EM allowed them to show that axosomes were derived from but distinct from axon tips. Axosome formation may...