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Drosophila dscam proteins regulate postsynaptic specificity at multiple-contact synapses.

ABSTRACT: In both vertebrate and invertebrate visual systems, neurons form multiple-contact synapses at which a single presynaptic site releases neurotransmitter upon a discrete combination of different postsynaptic cells. Recognition mechanisms underlying the assembly of such synapses are not known. In Drosophila, photoreceptor terminals form tetrad synapses that incorporate an invariable pair of postsynaptic elements, one each from lamina interneuron L1 and L2, and two elements from other cells. Here, we demonstrate that Drosophila Dscam1 and Dscam2, genes encoding homophilic repulsive proteins, act redundantly to ensure the invariable combination of L1 and L2 postsynaptic elements at all tetrads. We demonstrate that this strict pairing is lost in Dscam1;Dscam2 double mutants. Thus, removing these two repulsive proteins allows elements from the same cell to incorporate into the same postsynaptic tetrad, altering the specificity of photoreceptor transmission. We propose that Dscams regulate synaptic specificity by excluding inappropriate partners at multiple-contact synapses.

SUBMITTER: Millard SS

PROVIDER: S-EPMC3307816 | biostudies-literature | 2010 Sep

REPOSITORIES: biostudies-literature

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Drosophila dscam proteins regulate postsynaptic specificity at multiple-contact synapses.

Millard S Sean SS Lu Zhiyuan Z Zipursky S Lawrence SL Meinertzhagen Ian A IA

Neuron 20100901 5

In both vertebrate and invertebrate visual systems, neurons form multiple-contact synapses at which a single presynaptic site releases neurotransmitter upon a discrete combination of different postsynaptic cells. Recognition mechanisms underlying the assembly of such synapses are not known. In Drosophila, photoreceptor terminals form tetrad synapses that incorporate an invariable pair of postsynaptic elements, one each from lamina interneuron L1 and L2, and two elements from other cells. Here, w ...[more]

PMID: 20826308

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Project description:The location of proteins that contribute to synaptic function has been widely studied in vertebrate synapses, far more than at model synapses of the genetically manipulable fruit fly, Drosophila melanogaster. Drosophila photoreceptor terminals have been extensively exploited to characterize the actions of synaptic genes, and their distinct and repetitive synaptic ultrastructure is anatomically well suited for such studies. Synaptic release sites include a bipartite T-bar ribbon, comprising a platform surmounting a pedestal. So far, little is known about the composition and precise location of proteins at either the T-bar ribbon or its associated synaptic organelles, knowledge of which is required to understand many details of synaptic function. We studied the localization of candidate proteins to pre- or postsynaptic organelles, by using immuno-electron microscopy with the pre-embedding method, after first validating immunolabeling by confocal microscopy. We used monoclonal antibodies against Bruchpilot, epidermal growth factor receptor pathway substrate clone 15 (EPS-15), and cysteine string protein (CSP), all raised against a fly head homogenate, as well as sea urchin kinesin (antibody SUK4) and Discs large (DLG). All these antibodies labeled distinct synaptic structures in photoreceptor terminals in the first optic neuropil, the lamina, as did rabbit anti-DPAK (Drosophila p21 activated kinase) and anti-Dynamin. Validating reports from light microscopy, immunoreactivity to Bruchpilot localized to the edge of the platform, and immunoreactivity to SUK4 localized to the pedestal of the T-bar ribbon. Anti-DLG recognized the photoreceptor head of capitate projections, invaginating organelles from surrounding glia. For synaptic vesicles, immunoreactivity to EPS-15 localized to sites of endocytosis, and anti-CSP labeled vesicles lying close to the T-bar ribbon. These results provide markers for synaptic sites, and a basis for further functional studies.

Dataset Information

Drosophila dscam proteins regulate postsynaptic specificity at multiple-contact synapses.

Publications

Drosophila dscam proteins regulate postsynaptic specificity at multiple-contact synapses.

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