A Vast Repertoire of Dscam Binding Specificities Arises from Modular Interactions of Variable Ig Domains

Department of Biological Chemistry, Howard Hughes Medical Institute, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90095-1662, USA.
Cell (Impact Factor: 32.24). 09/2007; 130(6):1134-45. DOI: 10.1016/j.cell.2007.08.026
Source: PubMed


Dscam encodes a family of cell surface proteins required for establishing neural circuits in Drosophila. Alternative splicing of Drosophila Dscam can generate 19,008 distinct extracellular domains containing different combinations of three variable immunoglobulin domains. To test the binding properties of many Dscam isoforms, we developed a high-throughput ELISA-based binding assay. We provide evidence that 95% (>18,000) of Dscam isoforms exhibit striking isoform-specific homophilic binding. We demonstrate that each of the three variable domains binds to the same variable domain in an opposing isoform and identify the structural elements that mediate this self-binding of each domain. These studies demonstrate that self-binding domains can assemble in different combinations to generate an enormous family of homophilic binding proteins. We propose that this vast repertoire of Dscam recognition molecules is sufficient to provide each neuron with a unique identity and homotypic binding specificity, thereby allowing neuronal processes to distinguish between self and nonself.

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    • "In Drosophila and other invertebrates, self-avoidance is mediated by Dscam1 proteins—immunoglobulin superfamily members produced by alternative splicing of the DSCAM1 premRNA . This cell-autonomous and stochastic alternative splicing can theoretically produce up to 19,008 Dscam1 isoforms with distinct ectodomains, each of which have highly specific homophilic trans binding specificity (Hattori et al., 2008; Miura et al., 2013; Schmucker et al., 2000; Wojtowicz et al., 2007). Distinct cell-surface identities are generated in Drosophila by the stochastic expression of a small set of Dscam1 isoforms in each neuron (Miura et al., 2013). "
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    ABSTRACT: Self-avoidance, a process preventing interactions of axons and dendrites from the same neuron during development, is mediated in vertebrates through the stochastic single-neuron expression of clustered protocadherin protein isoforms. Extracellular cadherin (EC) domains mediate isoform-specific homophilic binding between cells, conferring cell recognition through a poorly understood mechanism. Here, we report crystal structures for the EC1-EC3 domain regions from four protocadherin isoforms representing the α, β, and γ subfamilies. All are rod shaped and monomeric in solution. Biophysical measurements, cell aggregation assays, and computational docking reveal that trans binding between cells depends on the EC1-EC4 domains, which interact in an antiparallel orientation. We also show that the EC6 domains are required for the formation of cis-dimers. Overall, our results are consistent with a model in which protocadherin cis-dimers engage in a head-to-tail interaction between EC1-EC4 domains from apposed cell surfaces, possibly forming a zipper-like protein assembly, and thus providing a size-dependent self-recognition mechanism.
    Cell 10/2015; 163(3). DOI:10.1016/j.cell.2015.09.026 · 32.24 Impact Factor
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    • "Cell adhesion molecules are transmembrane proteins, which play a role in recognition of synaptic partners during the initial contact and provide specificity of synaptic connections (Meijers et al., 2007; Wojtowicz et al., 2007). In addition, cell adhesion molecules have been shown to play a role in the process of synaptic maturation following the initial contact, in the recruitment of synaptic proteins as well as in maintaining proper synaptic function throughout the lifetime of the synapse (Dalva et al., 2007; Krueger et al., 2012; Thalhammer and Cingolani, 2013). "
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    ABSTRACT: Synaptic connections in our brains change continuously and throughout our lifetime. Despite ongoing synaptic changes, a healthy balance between excitation and inhibition is maintained by various forms of homeostatic and activity-dependent adaptations, ensuring stable functioning of neuronal networks. In this review we summarize experimental evidence for activity-dependent changes occurring in inhibitory axons, in cultures as well as in vivo. Axons form many presynaptic terminals, which are dynamic structures sharing presynaptic material along the axonal shaft. We discuss how internal (e.g., vesicle sharing) and external factors (e.g., binding of cell adhesion molecules or secreted factors) may affect the formation and plasticity of inhibitory synapses.
    Frontiers in Cellular Neuroscience 11/2013; 7:219. DOI:10.3389/fncel.2013.00219 · 4.29 Impact Factor
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    • "To address these problems, recent work has focused on the development of eukaryotic expression systems that use oligomerization to identify and assess low-affinity interactions between extracellular proteins. Clustering of ligands in various formats was found to be necessary for detecting interactions between Down syndrome cell adhesion molecule (DSCAM) splice variants (Wojtowicz et al., 2007). Multimerization was also shown to enhance detection of interactions among the extracellular domains (ECD) of zebrafish immunoglobulin superfamily (IgSF) and leucine-rich repeat (LRR) proteins in an aviditybased extracellular interaction screen (AVEXIS) (Bushell et al., 2008; Sö llner and Wright, 2009). "
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    ABSTRACT: Extracellular domains of cell surface receptors and ligands mediate cell-cell communication, adhesion, and initiation of signaling events, but most existing protein-protein "interactome" data sets lack information for extracellular interactions. We probed interactions between receptor extracellular domains, focusing on a set of 202 proteins composed of the Drosophila melanogaster immunoglobulin superfamily (IgSF), fibronectin type III (FnIII), and leucine-rich repeat (LRR) families, which are known to be important in neuronal and developmental functions. Out of 20,503 candidate protein pairs tested, we observed 106 interactions, 83 of which were previously unknown. We "deorphanized" the 20 member subfamily of defective-in-proboscis-response IgSF proteins, showing that they selectively interact with an 11 member subfamily of previously uncharacterized IgSF proteins. Both subfamilies interact with a single common "orphan" LRR protein. We also observed interactions between Hedgehog and EGFR pathway components. Several of these interactions could be visualized in live-dissected embryos, demonstrating that this approach can identify physiologically relevant receptor-ligand pairs.
    Cell 07/2013; 154(1):228-39. DOI:10.1016/j.cell.2013.06.006 · 32.24 Impact Factor
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