SummaryVPS35, a major component of the retromer, plays an important role in the selective endosome-to-Golgi retrieval of membrane proteins. Dysfunction of retromer is a risk factor for neurodegenerative disorders, but its function in developing mouse brain remains poorly understood. Here we provide evidence for VPS35 promoting dendritic growth and maturation, and axonal protein transport in developing mouse hippocampal neurons. Embryonic hippocampal CA1 neurons suppressing Vps35 expression by in utero electroporation of its micro RNAs displayed shortened apical dendrites, reduced dendritic spines, and swollen commissural axons in the neonatal stage, those deficits reflecting a defective protein transport/trafficking in developing mouse neurons. Further mechanistic studies showed that Vps35 depletion in neurons resulted in an impaired retrograde trafficking of BACE1 (β1-secretase) and altered BACE1 distribution. Suppression of BACE1 expression in CA1 neurons partially rescued both dendritic and axonal deficits induced by Vps35-deficiency. These results thus demonstrate that BACE1 acts as a critical cargo of retromer in vitro and in vivo, and suggest that VPS35 plays an essential role in regulating apical dendritic maturation and in preventing axonal spheroid formation in developing hippocampal neurons.

Formation of neural circuits depends on stable contacts between neuronal processes, mediated by interaction of cell adhesion molecules, including N-cadherin. In the present study, we found that activity-dependent dendrite arborization specifically requires Ncadherin-mediated extracellular neuron-neuron interaction, because the enhancement did not occur for neurons cultured in isolation or plated on an astrocyte monolayer and was abolished by a recombinant soluble N-cadherin ectodomain. Furthermore, depolarization elevated the level of membrane-associated cadherin/catenin complexes and surface N-cadherin. Importantly, surface N-cadherin elevation is specifically required for the maintenance of nascent dendrite arbors. Through loss-and gain-of-function approaches, we showed that N-cadherin-mediated dendrite growth requires association of the cadherin/catenin complex with the actin cytoskeleton. In summary, these results identify a previously unexplored and specific function for activity-induced, N-cadherin-mediated neuron-neuron contacts in the maintenance of dendrite arbors.cell adhesion molecule | catenin | actin D endrite growth and development are regulated by a combination of intrinsic programs and extrinsic signals, including neuronal activity, neurotrophins, morphogens, guidance cues, and cell adhesion molecules (CAMs), such as classical and seven-pass transmembrane cadherins (1-4). The establishment and maintenance of synaptic contacts between axons and dendrites also depend on CAMs, including neurexins/neurligins, EphB/ephrin-Bs, Neural-cadherin (N-cadherin), Ig superfamily members, and leucine-rich repeat containing synaptic adhesion molecules (5, 6). Importantly, the processes of axon/dendrite development and synapse formation are tightly correlated and regulated by neuronal activity (1,7). N-cadherin is a transmembrane CAM that interacts in a homophilic Ca 2+ -dependent manner through its extracellular ectodomains (8). Together with β-catenin and αN-catenin, it forms the cadherin/catenin complex, a main complex linking the extracellular environment to the actin cytoskeleton (9). The cadherin/catenin complex is present at high levels in both axons and dendrites (10), forming adherens junctions in epithelial cells and synaptic junctions in neurons.In the present study, we examined the function of N-cadherinmediated cell-cell interaction in the stabilization of dendritic arbors and in activity-dependent enhancement of dendritogenesis. Using a soluble N-cadherin ectodomain, we demonstrated a requirement for N-cadherin-mediated extracellular interaction in activity-dependent dendrite growth. Furthermore, by plating neurons in isolation, we showed that cell-cell contact is required for activity and N-cadherin-dependent dendrite growth. Finally, we showed that neuronal activity elevated surface N-cadherin level, an effect required for the maintenance of dendrite arbors. Together, these results identify a previously unexplored and specific function for activity-induced elevation of surface N-cadherin in the ma...

The human MET gene imparts a replicated risk for autism spectrum disorder (ASD), and is implicated in the structural and functional integrity of brain. MET encodes a receptor tyrosine kinase, MET, which plays a pleiotropic role in embryogenesis and modifies a large number of neurodevelopmental events. Very little is known, however, on how MET signaling engages distinct cellular events to collectively affect brain development in ASD-relevant disease domains. Here, we show that MET protein expression is dynamically regulated and compartmentalized in developing neurons. MET is heavily expressed in neuronal growth cones at early developmental stages and its activation engages small GTPase Cdc42 to promote neuronal growth, dendritic arborization, and spine formation. Genetic ablation of MET signaling in mouse dorsal pallium leads to altered neuronal morphology indicative of early functional maturation. In contrast, prolonged activation of MET represses the formation and functional maturation of glutamatergic synapses. Moreover, manipulating MET signaling levels in vivo in the developing prefrontal projection neurons disrupts the local circuit connectivity made onto these neurons. Therefore, normal time-delimited MET signaling is critical in regulating the timing of neuronal growth, glutamatergic synapse maturation and cortical circuit function. Dysregulated MET signaling may lead to pathological changes in forebrain maturation and connectivity, and thus contribute to the emergence of neurological symptoms associated with ASD.

No abstract