SynDIG1: An Activity-Regulated, AMPA- Receptor-Interacting Transmembrane Protein that Regulates Excitatory Synapse Development

Department of Pharmacology, School of Medicine, University of California, Davis, Davis, CA 95616, USA.
Neuron (Impact Factor: 15.05). 01/2010; 65(1):80-93. DOI: 10.1016/j.neuron.2009.12.021
Source: PubMed


During development of the central nervous system, precise synaptic connections between presynaptic and postsynaptic neurons are formed. While significant progress has been made in our understanding of AMPA receptor trafficking during synaptic plasticity, less is known about the molecules that recruit AMPA receptors to nascent synapses during synaptogenesis. Here we identify a type II transmembrane protein (SynDIG1) that regulates AMPA receptor content at developing synapses in dissociated rat hippocampal neurons. SynDIG1 colocalizes with AMPA receptors at synapses and at extrasynaptic sites and associates with AMPA receptors in heterologous cells and brain. Altered levels of SynDIG1 in cultured neurons result in striking changes in excitatory synapse number and function. SynDIG1-mediated synapse development is dependent on association with AMPA receptors via its extracellular C terminus. Intriguingly, SynDIG1 content in dendritic spines is regulated by neuronal activity. Altogether, we define SynDIG1 as an activity-regulated transmembrane protein that regulates excitatory synapse development.

Download full-text


Available from: Durga Mohapatra, Oct 09, 2015
31 Reads
  • Source
    • "These mechanisms have by and large been confirmed in slice cultures and in vivo (Fischer et al., 1998; Dunaevsky et al., 1999; Majewska and Sur, 2003). One approach that has been instrumental in the discovery of synaptogenic adhesion complexes is the use of co-cultures of neurons and heterologous cells (Scheiffele et al., 2000; Biederer et al., 2002; Graf et al., 2004; Kayser et al., 2006; Kim et al., 2006; Linhoff et al., 2009; Kalashnikova et al., 2010). In these mixed cultures, candidate synaptogenic proteins are expressed in heterologous cells and their ability to induce synaptogenesis in contacting neurons is assessed by immunostaining of synaptic markers (Biederer and Scheiffele, 2007). "
    [Show abstract] [Hide abstract]
    ABSTRACT: Presynaptic assembly involves the specialization of a patch of axonal membrane into a complex structure that supports synaptic vesicle exocytosis and neurotransmitter release. In mammalian neurons, presynaptic assembly is widely studied in a co-culture assay, where a synaptogenic cue expressed at the surface of a heterologous cell induces presynaptic differentiation in a contacting axon. This assay has led to the discovery of numerous synaptogenic proteins, but has not been used to probe neuronal mechanisms regulating presynaptic induction. The identification of regulatory pathways that fine-tune presynaptic assembly is hindered by the lack of adequate tools to quantitatively image this process. Here, we introduce an image-processing algorithm that identifies presynaptic clusters in mammalian co-cultures and extracts a range of synapse-specific parameters. Using this software, we assessed the intrinsic variability of this synaptic induction assay and probed the effect of eight neuronal microRNAs on presynaptic assembly. Our analysis revealed a novel role for miR-27b in augmenting the density of presynaptic clusters. Our software is applicable to a wide range of synaptic induction protocols (including spontaneous synaptogenesis observed in neuron cultures) and is a valuable tool to determine the subtle impact of disease-associated genes on presynaptic assembly.
    Frontiers in Cellular Neuroscience 03/2014; 8:66. DOI:10.3389/fncel.2014.00066 · 4.29 Impact Factor
  • Source
    • "Since then it was shown that stargazin belongs to the family of the transmembrane AMPA receptor regulatory proteins – TARPs [34]. Identification of the TARPs stimulated the discovery of the cohort of AMPAR's auxiliary subunits – CHIN2 and 3 [4], Shisa9 (CKAMP44; [5], SynDIG1 [35], GSG1L [36]. This list of potential AMPA receptor auxiliary subunits has kept growing [36], [37]. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Shisa9 (initially named CKAMP44) has been identified as auxiliary subunit of the AMPA-type glutamate receptors and was shown to modulate its physiological properties. Shisa9 is a type-I transmembrane protein and contains a C-terminal PDZ domain that potentially interacts with cytosolic proteins. In this study, we performed a yeast two-hybrid screening that yielded eight PDZ domain-containing interactors of Shisa9, which were independently validated. The identified interactors are known scaffolding proteins residing in the neuronal postsynaptic density. To test whether C-terminal scaffolding interactions of Shisa9 affect synaptic AMPA receptor function in the hippocampus, we disrupted these interactions using a Shisa9 C-terminal mimetic peptide. In the absence of scaffolding interactions of Shisa9, glutamatergic AMPA receptor-mediated synaptic currents in the lateral perforant path of the mouse hippocampus had a faster decay time, and paired-pulse facilitation was reduced. Furthermore, disruption of the PDZ interactions between Shisa9 and its binding partners affected hippocampal network activity. Taken together, our data identifies novel interaction partners of Shisa9, and shows that the C-terminal interactions of Shisa9 through its PDZ domain interaction motif are important for AMPA receptor synaptic and network functions.
    PLoS ONE 02/2014; 9(2):e87360. DOI:10.1371/journal.pone.0087360 · 3.23 Impact Factor
  • Source
    • "SynDIG1 has no known sequence homology with other postsynaptic proteins [8] [17], so we are not able to predict what type of protein-protein interactions SynDIG1 may form to regulate synaptogenesis. Interestingly, SynDIG4 (PRRT1) is thought to bind AMPARs directly in vivo [15] [16] and SynDIG1 was found to be capable of homodimerization [17], so it may be that SynDIG1 forms heterodimers with other SynDIG family members to exert its effects. Further research on binding partners of SynDIG1 will certainly prove useful in determining the specific mechanism by which SynDIG1 regulates excitatory synapse number. "
    [Show abstract] [Hide abstract]
    ABSTRACT: AMPA receptors-mediators of fast, excitatory transmission and synaptic plasticity in the brain-achieve great functional diversity through interaction with different auxiliary subunits, which alter both the trafficking and biophysical properties of these receptors. In the past several years an abundance of new AMPA receptor auxiliary subunits have been identified, adding astounding variety to the proteins known to directly bind and modulate AMPA receptors. SynDIG1 was recently identified as a novel AMPA receptor interacting protein that directly binds to the AMPA receptor subunit GluA2 in heterologous cells. Functionally, SynDIG1 was found to regulate the strength and density of AMPA receptor containing synapses in hippocampal neurons, though the way in which SynDIG1 exerts these effects remains unknown. Here, we aimed to determine if SynDIG1 acts as a traditional auxiliary subunit, directly regulating the function and localization of AMPA receptors in the rat hippocampus. We find that, unlike any of the previously characterized AMPA receptor auxiliary subunits, SynDIG1 expression does not impact AMPA receptor gating, pharmacology, or surface trafficking. Rather, we show that SynDIG1 regulates the number of functional excitatory synapses, altering both AMPA and NMDA receptor mediated transmission. Our findings suggest that SynDIG1 is not a typical auxiliary subunit to AMPA receptors, but instead is a protein critical to excitatory synaptogenesis.
    PLoS ONE 06/2013; 8(6):e66171. DOI:10.1371/journal.pone.0066171 · 3.23 Impact Factor
Show more