Transcytosis-mediated anterograde transport of TrkA receptors controls formation of presynaptic sites in sympathetic neurons
In neurons, many membrane proteins, synthesized in cell bodies, must be efficiently delivered to axons to influence neuronal connectivity. Transcytosis is an atypical transport mode, where membrane proteins internalized from soma surfaces are anterogradely transported to axons. Here, we define the trafficking dynamics and the transport vesicles involved in transcytosis of TrkA neurotrophin receptors and demonstrate that transcytosis controls formation of presynaptic sites in sympathetic neurons. Live imaging and electron microscopy in compartmentalized cultures revealed that soma surface-derived TrkA receptors undergo dynamic movements in axons and are housed in endosomes and multi-vesicular bodies. Soma-surface labeled TrkA appear in nerve terminals, demonstrating transcytosis occurs in vivo. Notably, transcytosed TrkA receptors are enriched at presynaptic varicosities. Disruption of transcytosis impairs the number and morphology of presynaptic sites and decreases synaptic transmission. These findings provide mechanistic insight into an atypical mode of receptor trafficking and highlights its physiological relevance in sympathetic neuron connectivity.