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Highlights d LDAF1 and seipin form an 600 kDa oligomeric complex in the ER bilayer d The LDAF1-seipin complex determines the sites of lipid droplet formation in the ER d LDAF1 dissociates from seipin and moves to the growing lipid droplet surface d LDAF1 facilitates lipid droplet formation at low ER triglyceride concentration

Activity-dependent changes in gene-expression are believed to underlie the molecular representation of memory. In this study, we report that in vivo activation of neurons rapidly induces the CREB-regulated microRNA miR-132. To determine if production of miR-132 is regulated by neuronal activity its expression in mouse brain was monitored by quantitative RT-PCR (RT-qPCR). Pilocarpine-induced seizures led to a robust, rapid, and transient increase in the primary transcript of miR-132 (pri-miR-132) followed by a subsequent rise in mature microRNA (miR-132). Activation of neurons in the hippocampus, olfactory bulb, and striatum by contextual fear conditioning, odor-exposure, and cocaine-injection, respectively, also increased pri-miR-132. Induction kinetics of pri-miR-132 were monitored and found to parallel those of immediate early genes, peaking at 45 minutes and returning to basal levels within two hours of stimulation. Expression levels of primary and mature-miR-132 increased significantly between postnatal days 10 and 24. We conclude that miR-132 is an activity-dependent microRNA in vivo, and may contribute to the long-lasting proteomic changes required for experience-dependent neuronal plasticity.

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The synaptonemal complex (SC) is an ultrastructurally conserved proteinaceous structure that holds homologous chromosomes together and is required for the stabilization of pairing interactions and the completion of crossover (CO) formation between homologs during meiosis I. Here, we identify a novel role for a central region component of the SC, SYP-4, in negatively regulating formation of recombination-initiating double-strand breaks (DSBs) via a feedback loop triggered by crossover designation in C. elegans. We found that SYP-4 is phosphorylated dependent on Polo-like kinases PLK-1/2. SYP-4 phosphorylation depends on DSB formation and crossover designation, is required for stabilizing the SC in pachytene by switching the central region of the SC from a more dynamic to a less dynamic state, and negatively regulates DSB formation. We propose a model in which Polo-like kinases recognize crossover designation and phosphorylate SYP-4 thereby stabilizing the SC and making chromosomes less permissive for further DSB formation.DOI: http://dx.doi.org/10.7554/eLife.23437.001

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Integrin αβ heterodimer cell surface receptors mediate adhesive interactions that provide traction for cell migration. Here, we test whether the integrin, when engaged to an extracellular ligand and the cytoskeleton, adopts a specific orientation dictated by the direction of actin flow on the surface of migrating cells. We insert GFP into the rigid, ligand-binding head of the integrin, model with Rosetta the orientation of GFP and its transition dipole relative to the integrin head, and measure orientation with fluorescence polarization microscopy. Cytoskeleton and ligand-bound integrins orient in the same direction as retrograde actin flow with their cytoskeleton-binding β-subunits tilted by applied force. The measurements demonstrate that intracellular forces can orient cell surface integrins and support a molecular model of integrin activation by cytoskeletal force. Our results place atomic, Å-scale structures of cell surface receptors in the context of functional and cellular, μm-scale measurements.

Overexpression of the amyloid precursor protein (APP) in hippocampal neurons leads to elevated ␤-amyloid peptide (A␤) production and consequent depression of excitatory transmission. The precise mechanisms underlying APP-induced synaptic depression are poorly understood. Uncovering these mechanisms could provide insight into how neuronal function is compromised before cell death during the early stages of Alzheimer's disease. Here we verify that APP up-regulation leads to depression of transmission in cultured hippocampal autapses; and we perform whole-cell recording, FM imaging, and immunocytochemistry to identify the specific mechanisms accounting for this depression. We find that APP overexpression leads to postsynaptic silencing through a selective reduction of ␣-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor-mediated currents. This effect is likely mediated by A␤ because expression of mutant APP incapable of producing A␤ did not depress transmission. In addition, although we eliminate presynaptic silencing as a mechanism underlying APP-mediated inhibition of transmission, we did observe an A␤-induced presynaptic deficit in vesicle recycling with sustained stimulation. These findings demonstrate that APP elevation disrupts both presynaptic and postsynaptic compartments.Alzheimer's disease ͉ synaptic transmission ͉ glutamate receptor ͉ synaptic vesicle cycling T he early stages of Alzheimer's disease (AD) are characterized by cognitive deficits that are likely the result of impairments of synaptic function before either plaque formation or cell death (1-4). Identifying these impairments and the mechanisms that underlie them is a critical step in the development of novel therapies aimed at improving cognitive function in AD patients.A critical role for amyloid precursor protein (APP) and its cleavage products is indicated by the finding that mutations in the APP gene are linked to the inherited form of the disease, familial early onset AD (FAD; ref. 5). In addition, animal models that express the human APP protein bearing FAD-linked mutations recapitulate key features of early stage AD pathology (6, 7). Notably, levels of the ␤-amyloid peptide (A␤), which is generated through sequential cleavage of APP by ␤-APPcleaving enzyme 1 (BACE) and ␥-secretase, are greatly elevated in these model mice (7).Three lines of evidence strongly suggest that A␤ has acute effects on synaptic function: (i) Intracerebroventricular injection of naturally secreted A␤ is sufficient to disrupt cognitive function in a rapid and transient manner (8).(ii) Active immunization with A␤ peptide can protect against, or even reverse, AD-like neuropathology and behavioral deficits of AD model mice (9, 10). (iii) Passive immunization with anti-A␤ antibody can rapidly reverse memory deficits of AD model mice (11-13).Consistent with this notion, rapid viral-mediated upregulation of APP and consequent elevation of A␤ production in cultured hippocampal slices has been shown to depress excitatory transmission by decreasing the num...