Neurexin-1β Binding to Neuroligin-1 Triggers the Preferential Recruitment of PSD-95 versus Gephyrin through Tyrosine Phosphorylation of Neuroligin-1

Adhesion between neurexin-1β (Nrx1β) and neuroligin-1 (Nlg1) induces early recruitment of the postsynaptic density protein 95 (PSD-95) scaffold; however, the associated signaling mechanisms are unknown. To dissociate the effects of ligand binding and receptor multimerization, we compared conditions in which Nlg1 in neurons was bound to Nrx1β or nonactivating HA antibodies. Time-lapse imaging, fluorescence recovery after photobleaching, and single-particle tracking demonstrated that in addition to aggregating Nlg1, Nrx1β binding stimulates the interaction between Nlg1 and PSD-95. Phosphotyrosine immunoblots and pull-down of gephyrin by Nlg1 peptides in vitro showed that Nlg1 can be phosphorylated at a unique tyrosine (Y782), preventing gephyrin binding. Expression of Nlg1 point mutants in neurons indicated that Y782 phosphorylation controls the preferential binding of Nlg1 to PSD-95 versus gephyrin, and accordingly the formation of inhibitory and excitatory synapses. We propose that ligand-induced changes in the Nlg1 phosphotyrosine level control the balance between excitatory and inhibitory scaffold assembly during synapse formation and stabilization

A unique intracellular tyrosine in neuroligin-1 regulates AMPA receptor recruitment during synapse differentiation and potentiation

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Protein kinase D promotes plasticity-induced F-actin stabilization in dendritic spines and regulates memory formation

Actin turnover in dendritic spines influences spine development, morphology, and plasticity, with functional consequences on learning and memory formation. In nonneuronal cells, protein kinase D (PKD) has an important role in stabilizing F-actin via multiple molecular pathways. Using in vitro models of neuronal plasticity, such as glycine-induced chemical long-term potentiation (LTP), known to evoke synaptic plasticity, or long-term depolarization block by KCl, leading to homeostatic morphological changes, we show that actin stabilization needed for the enlargement of dendritic spines is dependent on PKD activity. Consequently, impaired PKD functions attenuate activity-dependent changes in hippocampal dendritic spines, including LTP formation, cause morphological alterations in vivo, and have deleterious consequences on spatial memory formation. We thus provide compelling evidence that PKD controls synaptic plasticity and learning by regulating actin stability in dendritic spines

Protein Kinase D Controls the Integrity of Golgi Apparatus and the Maintenance of Dendritic Arborization in Hippocampal Neurons

Protein kinase D (PKD) is known to participate in various cellular functions, including secretory vesicle fission from the Golgi and plasma membrane-directed transport. Here, we report on expression and function of PKD in hippocampal neurons. Expression of an enhanced green fluorescent protein (EGFP)-tagged PKD activity reporter in mouse embryonal hippocampal neurons revealed high endogenous PKD activity at the Golgi complex and in the dendrites, whereas PKD activity was excluded from the axon in parallel with axonal maturation. Expression of fluorescently tagged wild-type PKD1 and constitutively active PKD1S738/742E (caPKD1) in neurons revealed that both proteins were slightly enriched at the trans-Golgi network (TGN) and did not interfere with its thread-like morphology. By contrast, expression of dominant-negative kinase inactive PKD1K612W (kdPKD1) led to the disruption of the neuronal Golgi complex, with kdPKD1 strongly localized to the TGN fragments. Similar findings were obtained from transgenic mice with inducible, neuron-specific expression of kdPKD1-EGFP. As a prominent consequence of kdPKD1 expression, the dendritic tree of transfected neurons was reduced, whereas caPKD1 increased dendritic arborization. Our results thus provide direct evidence that PKD activity is selectively involved in the maintenance of dendritic arborization and Golgi structure of hippocampal neurons