160 research outputs found
Neuronal Profilin Isoforms Are Addressed by Different Signalling Pathways
Profilins are prominent regulators of actin dynamics. While most mammalian cells express only one profilin, two isoforms, PFN1 and PFN2a are present in the CNS. To challenge the hypothesis that the expression of two profilin isoforms is linked to the complex shape of neurons and to the activity-dependent structural plasticity, we analysed how PFN1 and PFN2a respond to changes of neuronal activity. Simultaneous labelling of rodent embryonic neurons with isoform-specific monoclonal antibodies revealed both isoforms in the same synapse. Immunoelectron microscopy on brain sections demonstrated both profilins in synapses of the mature rodent cortex, hippocampus and cerebellum. Both isoforms were significantly more abundant in postsynaptic than in presynaptic structures. Immunofluorescence showed PFN2a associated with gephyrin clusters of the postsynaptic active zone in inhibitory synapses of embryonic neurons. When cultures were stimulated in order to change their activity level, active synapses that were identified by the uptake of synaptotagmin antibodies, displayed significantly higher amounts of both isoforms than non-stimulated controls. Specific inhibition of NMDA receptors by the antagonist APV in cultured rat hippocampal neurons resulted in a decrease of PFN2a but left PFN1 unaffected. Stimulation by the brain derived neurotrophic factor (BDNF), on the other hand, led to a significant increase in both synaptic PFN1 and PFN2a. Analogous results were obtained for neuronal nuclei: both isoforms were localized in the same nucleus, and their levels rose significantly in response to KCl stimulation, whereas BDNF caused here a higher increase in PFN1 than in PFN2a. Our results strongly support the notion of an isoform specific role for profilins as regulators of actin dynamics in different signalling pathways, in excitatory as well as in inhibitory synapses. Furthermore, they suggest a functional role for both profilins in neuronal nuclei
Massive mortality of invasive bivalves as a potential resource subsidy for the adjacent terrestrial food web
Large-scale mortality of invasive bivalves
was observed in the River Danube basin in the autumn
of 2011 due to a particularly low water discharge. The
aim of this study was to quantify and compare the
biomass of invasive and native bivalve die-offs
amongst eight different sites and to assess the potential
role of invasive bivalve die-offs as a resource subsidy
for the adjacent terrestrial food web. Invasive bivalve
die-offs dominated half of the study sites and their
highest density and biomass were recorded at the
warm water effluent. The density and biomass values
recorded in this study are amongst the highest values
recorded for aquatic ecosystems and show that a
habitat affected by heated water can sustain an extremely high biomass of invasive bivalves. These
mortalities highlight invasive bivalves as a major
resource subsidy, possibly contributing remarkable
amounts of nutrients and energy to the adjacent
terrestrial ecosystem. Given the widespread occurrence
of these invasive bivalves and the predicted
increase in the frequency and intensity of extreme
climatic events, the ecological impacts generated by
their massive mortalities should be taken into account
in other geographical areas as well.The authors are grateful to David Strayer for valuable comments on a previous version of the manuscript. Special thanks to the Danube-Ipoly National Park for the help in field work. Ronaldo Sousa was supported by the project "ECOIAS" funded by the Portuguese Foundation for the Science and the Technology and COMPETE funds (contract: PTDC/AAC-AMB/116685/2010)
Discovery of Inhibitors of Leishmania β-1,2-Mannosyltransferases Using a Click-Chemistry-Derived Guanosine Monophosphate Library
Leishmania spp. are a medically important group of protozoan parasites that synthesize a novel intracellular carbohydrate reserve polymer termed mannogen. Mannogen is a soluble homopolymer of β-1,2-linked mannose residues that accumulates in the major pathogenic stages in the sandfly vector and mammalian host. While several steps in mannogen biosynthesis have been defined, none of the enzymes have been isolated or characterized. We report the development of a simple assay for the GDP-mannose–dependent β-1,2-mannosyltransferases involved in mannogen synthesis. This assay utilizes octyl α-d-mannopyranoside to prime the formation of short mannogen oligomers up to 5 mannose residues. This assay was used to screen a focussed library of 44 GMP-triazole adducts for inhibitors. Several compounds provided effective inhibition of mannogen β-1,2-mannosyltransferases in a cell-free membrane preparation. This assay and inhibitor compounds will be useful for dissecting the role of different mannosyltransferases in regulating de novo biosynthesis and elongation reactions in mannogen metabolism
Amyloid Precursor Protein Is Trafficked and Secreted via Synaptic Vesicles
A large body of evidence has implicated amyloid precursor protein (APP) and its
proteolytic derivatives as key players in the physiological context of neuronal
synaptogenesis and synapse maintenance, as well as in the pathology of
Alzheimer's Disease (AD). Although APP processing and release are known to
occur in response to neuronal stimulation, the exact mechanism by which APP
reaches the neuronal surface is unclear. We now demonstrate that a small but
relevant number of synaptic vesicles contain APP, which can be released during
neuronal activity, and most likely represent the major exocytic pathway of APP.
This novel finding leads us to propose a revised model of presynaptic APP
trafficking that reconciles existing knowledge on APP with our present
understanding of vesicular release and recycling
Eps8 Regulates Axonal Filopodia in Hippocampal Neurons in Response to Brain-Derived Neurotrophic Factor (BDNF)
A novel signaling cascade controlling actin polymerization in response to extracellular signals regulates filopodia formation and likely also neuronal synapse formation
Long-Term Relationships between Synaptic Tenacity, Synaptic Remodeling, and Network Activity
Long term time-lapse imaging reveals that individual synapses undergo significant structural remodeling not only when driven by activity, but also when network activity is absent, raising questions about how reliably individual synapses maintain connections
Synapse Clusters Are Preferentially Formed by Synapses with Large Recycling Pool Sizes
Synapses are distributed heterogeneously in neural networks. The relationship between the spatial arrangement of synapses and an individual synapse's structural and functional features remains to be elucidated. Here, we examined the influence of the number of adjacent synapses on individual synaptic recycling pool sizes. When measuring the discharge of the styryl dye FM1–43 from electrically stimulated synapses in rat hippocampal tissue cultures, a strong positive correlation between the number of neighbouring synapses and recycling vesicle pool sizes was observed. Accordingly, vesicle-rich synapses were found to preferentially reside next to neighbours with large recycling pool sizes. Although these synapses with large recycling pool sizes were rare, they were densely arranged and thus exhibited a high amount of release per volume. To consolidate these findings, functional terminals were marked by live-cell antibody staining with anti-synaptotagmin-1-cypHer or overexpression of synaptopHluorin. Analysis of synapse distributions in these systems confirmed the results obtained with FM 1–43. Our findings support the idea that clustering of synapses with large recycling pool sizes is a distinct developmental feature of newly formed neural networks and may contribute to functional plasticity
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