Figure 1.

Endocytosis in neurons. (A) Upon ligand binding, Trk receptors are activated and recruit PI3 kinase, Ras/MAPK, and PLC-γ to initiate downstream signaling pathways. (B) Internalization of neurotrophin/Trk complexes can occur via clathrin-dependent mechanisms to give rise to early endosomes, or via macropinocytosis, which gives rise to multivesicular bodies (MVBs). (C) The endosomal pathway involves maturation from early endosomes associated with Rab5 to late endosomes associated with Rab7. Vesicles are degraded in lysosomes or can be recycled back to the membrane through association with Rab11. (D) In neurons, endosomes are trafficked long distances along the axon by dynein-mediated retrograde transport toward the cell body, or by kinesin-mediated anterograde transport toward the distal axon.