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Alejandro Vila, Christopher Whitaker, John O'Brien; A synaptic scaffold complex unique to horizontal cell processes contacting photoreceptors. Invest. Ophthalmol. Vis. Sci. 2013;54(15):6091.
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© ARVO (1962-2015); The Authors (2016-present)
Synaptic plasticity is mediated by large suites of proteins. In most cases, these proteins are tethered together by synaptic scaffold proteins. Scaffold proteins have a large variety of protein interaction domains that allow many different proteins to be assembled into functional complexes. The unique distribution of scaffold proteins in restricted domains suggests that these proteins may be involved in synaptic processes that govern cell-to-cell communication from photoreceptors to horizontal cells (HC) and potentially from HC to photoreceptors.
To explore this hypothesis, we examined the association of synaptic scaffold protein Synapse-Associated Protein (SAP102) with known interacting partners by immunofluorescence and 3-D image reconstruction in rabbit retina. B-type HCs were dye injected with Neurobiotin in the presence of meclofenamic acid (MFA, 200 μM) to block gap junctions. We further examined the association of these proteins by co-immunoprecipitation and western blot techniques.
We found SAP102 exclusively localized in B-type HC processes. SAP102 distribution is highly restricted in both cone and rod invaginating synapses. Using exploratory immunohistochemistry we have identified kainate receptor subunits GluR6/7 and inward rectifying potassium channels KiR2.1 associated with SAP102 in photoreceptor invaginations. Cx57 makes gap junctions in the retina but does not co-localize with SAP102.
Proteins involved in feedforward and potentially feedback signaling are assembled by a scaffold. Further elucidation of the composition of complex can clarify the molecular mechanisms of feedback.
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