The tight spatial coupling of synaptic vesicles and voltage-gated Ca 2+ channels (Ca V s) ensures efficient action potential-triggered neurotransmitter release from presynaptic active zones (AZs). Rab-interacting molecule-binding proteins (RIM-BPs) interact with Ca 2+ channels and via RIM with other components of the release machinery. Although human RIM-BPs have been implicated in autism spectrum disorders, little is known about the role of mammalian RIM-BPs in synaptic transmission. We investigated RIM-BP2-deficient murine hippocampal neurons in cultures and slices. Short-term facilitation is significantly enhanced in both model systems. Detailed analysis in culture revealed a reduction in initial release probability, which presumably underlies the increased shortterm facilitation. Superresolution microscopy revealed an impairment in Ca V 2.1 clustering at AZs, which likely alters Ca 2+ nanodomains at release sites and thereby affects release probability. Additional deletion of RIM-BP1 does not exacerbate the phenotype, indicating that RIM-BP2 is the dominating RIM-BP isoform at these synapses.RIM-BP2 | calcium channel coupling | release probability | short-term plasticity | active zone structure A t the presynapse, coupling between action potentials (APs) and synaptic vesicle fusion is exquisitely precise, ensuring high temporal fidelity of neuron-to-neuron signaling in the nervous system. Two properties are thought to be responsible for this remarkable precision: a highly efficient release apparatus that transduces Ca 2+ signals into vesicle fusion and a tightly organized active zone (AZ), where the release apparatus and voltage-gated Ca 2+ channels (Ca V s) are spatially coupled. Rab-interacting molecules (RIM) are thought to contribute to both properties, because loss of RIM impairs vesicle priming (1) and Ca V localization at the AZ (2). RIM-binding proteins (RIM-BPs) directly interact with RIM (3), the pore-forming subunits of Ca V 1 and Ca V 2 channels (2, 4, 5), and Bassoon (5), and have therefore been suggested to play a role in presynaptic Ca V localization. The Drosophila homolog of RIM-binding proteins (DRBP) is indeed crucial for neurotransmitter release at the AZ of neuromuscular junctions (NMJs) because loss of DRBP reduces Ca V abundance and impairs the integrity of the AZ scaffold (6). DRBP-deficient flies show severe impairment of neurotransmitter release along with increased short-term facilitation (6, 7).Recently, Acuna et al. (8) published a report on the combined loss of RIM-BP1 and RIM-BP2 in mouse synapses. The authors report that although RIM-BPs are not essential for synaptic transmission, AP-triggered neurotransmitter release is more variable and the sensitivity to the Ca 2+ chelator EGTA is increased at the Calyx of Held, suggesting a larger coupling distance of Ca V and the release machinery.In the present study, we further investigated the consequences of constitutive deletion of RIM-BP2 on the structure and function of mouse hippocampal synapses. We show that loss of RIM-BP2 lead...

Neddylation is a ubiquitylation-like pathway that controls cell cycle and proliferation by covalently conjugating Nedd8 to specific targets. However, its role in neurons, nonreplicating postmitotic cells, remains unexplored. Here we report that Nedd8 conjugation increased during postnatal brain development and is active in mature synapses, where many proteins are neddylated. We show that neddylation controls spine development during neuronal maturation and spine stability in mature neurons. We found that neddylated PSD-95 was present in spines and that neddylation on Lys202 of PSD-95 is required for the proactive role of the scaffolding protein in spine maturation and synaptic transmission. Finally, we developed Nae1(CamKIIα-CreERT2) mice, in which neddylation is conditionally ablated in adult excitatory forebrain neurons. These mice showed synaptic loss, impaired neurotransmission and severe cognitive deficits. In summary, our results establish neddylation as an active post-translational modification in the synapse regulating the maturation, stability and function of dendritic spines.

MicroRNAs (miRNAs) are conserved noncoding RNAs that function as posttranscriptional regulators of gene expression. miR-9 is one of the most abundant miRNAs in the brain. Although the function of miR-9 has been well characterized in neural progenitors, its role in dendritic and synaptic development remains largely unknown. In order to target miR-9 in vivo, we developed a transgenic miRNA sponge mouse line allowing conditional inactivation of the miR-9 family in a spatio-temporal-controlled manner. Using this novel approach, we found that miR-9 controls dendritic growth and synaptic transmission in vivo. Furthermore, we demonstrate that miR-9-mediated downregulation of the transcriptional repressor REST is essential for proper dendritic growth.DOI: http://dx.doi.org/10.7554/eLife.02755.001

Highlights d RBP and RIM are needed for sufficient Ca 2+ influx d RBP2 primes synaptic vesicles via Munc13-1 at small central synapses d RBP2 controls short-term plasticity by vesicle priming or Ca 2+ -channel recruitment

Neuromodulators bind to pre-and postsynaptic G protein-coupled receptors (GPCRs), are able to quickly change intracellular cyclic AMP (cAMP) and Ca 2+ levels, and are thought to play important roles in neuropsychiatric and neurodegenerative diseases. Here, we discovered in human neurons an unanticipated presynaptic mechanism that acutely changes synaptic ultrastructure and regulates synaptic communication. Activation of neuromodulator receptors bidirectionally controlled synaptic vesicle numbers within nerve terminals. This control correlated with changes in the levels of cAMP-dependent protein kinase A-mediated phosphorylation of synapsin-1. Using a conditional deletion approach, we reveal that the neuromodulator-induced control of synaptic vesicle numbers was largely dependent on synapsin-1. We propose a mechanism whereby non-phosphorylated synapsin-1 ''latches'' synaptic vesicles to presynaptic clusters at the active zone. cAMP-dependent phosphorylation of synapsin-1 then removes the vesicles. cAMP-independent dephosphorylation of synapsin-1 in turn recruits vesicles. Synapsin-1 thereby bidirectionally regulates synaptic vesicle numbers and modifies presynaptic neurotransmitter release as an effector of neuromodulator signaling in human neurons.