Positioning of Rab11-positive recycling endosomes regulates synapse architecture and growth cone dynamics

Recycling endosomes are involved in various cargo trafficking and polarization processes. In hippocampal neurons they deliver AMPA receptors to the postsynapse and are required for axonal outgrowth. However, how the positioning of recycling endosomes affects synapse organization and functioning or growth cone dynamics has never been directly explored. We used live-cell imaging in hippocampal neuron cultures to show that intracellular AMPARs are transported in Rab11-positive recycling endosomes, which frequently enter dendritic spines and depend on the microtubule and actin cytoskeleton. By using chemically-induced dimerization systems to recruit kinesin and myosin motors to Rab11-positive recycling endosomes, we control their trafficking and found that induced removal of recycling endosomes from spines decreases surface AMPAR expression and postsynaptic scaffold protein clusters. Moreover, the development of optogenetic dimerization systems now allows us to manipulate the positioning of recycling endosomes with high spatiotemporal precision. These experiments show that axon outgrowth depends on the presence of Rab-11 positive recycling endosomes in growth cones.