Axon branch removal at developing synapses by axosome shedding.
In many parts of the developing nervous system, the number of axonal inputs to each postsynaptic cell is dramatically reduced. This synapse elimination has been extensively studied at the neuromuscular junction, but how axons are lost is unknown. Here, we combine time-lapse imaging of fluorescently labeled axons and serial electron microscopy to show that axons at neuromuscular junctions are removed by an unusual cellular mechanism. As axons disappear, they shed numerous membrane bound remnants. These "axosomes" contain a high density of synaptic organelles and are formed by engulfment of axon tips by Schwann cells. After this engulfment, the axosome's contents mix with the cytoplasm of the glial cell. Axosome shedding might underlie other forms of axon loss and may provide a pathway for interactions between axons and glia.
Bishop
Derron L
DL
Department of Molecular and Cellular and Biology, Harvard University, Cambridge, MA 02138, USA.
Misgeld
Thomas
T
Walsh
Mark K
MK
Gan
Wen-Biao
WB
Lichtman
Jeff W
JW
D000818:Animals; D001369:Axons / Q000648:ultrastructure*; D003952:Diagnostic Imaging; D049452:Green Fluorescent Proteins; D007091:Image Processing, Computer-Assisted; D007150:Immunohistochemistry; D051379:Mice; D008822:Mice, Transgenic; D018613:Microscopy, Confocal; D046529:Microscopy, Electron, Transmission; D009469:Neuromuscular Junction / Q000648:ultrastructure*; D017933:Peripheral Nervous System / Q000254:growth & development*; D012583:Schwann Cells; D013569:Synapses / Q000648:ultrastructure*
D049452:Green Fluorescent Proteins