Local regulation of extracellular vesicle traffic by the synaptic endocytic machinery.

Neuronal extracellular vesicles (EVs) are locally released from presynaptic terminals, carrying cargoes critical for intercellular signaling and disease. EVs are derived from endosomes, but it is unknown how these cargoes are directed to the EV pathway rather than for conventional endolysosomal degradation. Here, we find that endocytic machinery plays an unexpected role in maintaining a release-competent pool of EV cargoes at synapses. Endocytic mutants, including nervous wreck (nwk), shibire/dynamin, and AP-2, unexpectedly exhibit local presynaptic depletion specifically of EV cargoes. Accordingly, nwk mutants phenocopy synaptic plasticity defects associated with loss of the EV cargo synaptotagmin-4 (Syt4) and suppress lethality upon overexpression of the EV cargo amyloid precursor protein (APP). These EV defects are genetically separable from canonical endocytic functions in synaptic vesicle recycling and synaptic growth. Endocytic machinery opposes the endosomal retromer complex to regulate EV cargo levels and acts upstream of synaptic cargo removal by retrograde axonal transport. Our data suggest a novel molecular mechanism that locally promotes cargo loading into synaptic EVs.

Opposing functions for retromer and Rab11 in extracellular vesicle traffic at presynaptic terminals.

Neuronal extracellular vesicles (EVs) play important roles in intercellular communication and pathogenic protein propagation in neurological disease. However, it remains unclear how cargoes are selectively packaged into neuronal EVs. Here, we show that loss of the endosomal retromer complex leads to accumulation of EV cargoes including amyloid precursor protein (APP), synaptotagmin-4 (Syt4), and neuroglian (Nrg) at Drosophila motor neuron presynaptic terminals, resulting in increased release of these cargoes in EVs. By systematically exploring known retromer-dependent trafficking mechanisms, we show that EV regulation is separable from several previously identified roles of neuronal retromer. Conversely, mutations in rab11 and rab4, regulators of endosome-plasma membrane recycling, cause reduced EV cargo levels, and rab11 suppresses cargo accumulation in retromer mutants. Thus, EV traffic reflects a balance between Rab4/Rab11 recycling and retromer-dependent removal from EV precursor compartments. Our data shed light on previous studies implicating Rab11 and retromer in competing pathways in Alzheimer's disease, and suggest that misregulated EV traffic may be an underlying defect.

Acute exogenous corticosterone treatments have few effects on courtship and pair bonding in zebra finches.

Stress impacts social relationships. In turn, social relationships buffer the stress response in some species. Studies that have investigated the role of corticosterone (CORT) on courtship, mate choice, mating, and pairing have found mixed results. We therefore tested the role of CORT in these steps of the pairing process in the monogamous zebra finch. Male and female zebra finches received either one of 2 doses of corticosterone (CORT, 10 µg and 20 µg, referred to as low and high dose) or a vehicle control (peanut oil). Subjects were then given the opportunity to pair in mixed sex aviaries. Courtship and pair bonding behaviors were observed over 3 days. Overall, zebra finches of both sexes were equally likely to pair or not pair regardless of treatment, although a high dose of CORT increased the latency to form a pair bond. There were no effects of CORT on courtship behavior in either sex, though the low dose increased undirected (non-courtship) singing in males relative to the high dose. Animals treated with CORT, regardless of dose, engaged in fewer copulations than did control animals. When we examined pairing behaviors, we found a decrease in co-nesting in low dose animals. Our results suggest that acute CORT has few effects on pair bonding, suggesting species-specific effects of CORT on behavior.