Abstract
Photoreceptor terminals contain post-synaptic density (PSD) proteins e.g., PSD-95/PSD-93, but their role at photoreceptor synapses is not known. PSDs are generally restricted to post-synaptic boutons in central neurons and form scaffolding with multiple proteins that have structural and functional roles in neuronal signaling. The Shank family of proteins (Shank 1–3) functions as putative anchoring proteins for PSDs and is involved in the organization of cytoskeletal/signaling complexes in neurons. Specifically, Shank 1 is restricted to neurons and interacts with both receptors and signaling molecules at central neurons to regulate plasticity. However, it is not known whether Shank 1 is expressed at photoreceptor terminals. In this study we have investigated Shank 1A localization in the outer retina at photoreceptor terminals. We find that Shank 1A is expressed presynaptically in cone pedicles, but not rod spherules, and it is absent from mice in which the Shank 1 gene is deleted. Shank 1A co-localizes with PSD-95, peanut agglutinin, a marker of cone terminals, and glycogen phosphorylase, a cone specific marker. These findings provide convincing evidence for Shank 1A expression in both the inner and outer plexiform layers, and indicate a potential role for PSD-95/Shank 1 complexes at cone synapses in the outer retina.
Highlights
Postsynaptic density (PSD) protein-95 family members (e.g., post-synaptic density (PSD)-95, PSD-93) are associated with presynaptic photoreceptor terminals in the outer plexiform layer (OPL) in the retina [1]
In the OPL, Shank 1A immunoreactivity consisted of large clusters at the base of the OPL that are indicative of cone pedicles (Fig. 1D–F)
Each cluster of Shank 1A puncta were in close apposition and distal to the tips of the dendrites of yellow fluorescent protein (YFP) cone bipolar cells (Fig. 1F), suggesting that Shank 1A was restricted to the presynaptic cone terminal, and not present in cone bipolar cell dendrites
Summary
Postsynaptic density (PSD) protein-95 family members (e.g., PSD-95, PSD-93) are associated with presynaptic photoreceptor terminals in the outer plexiform layer (OPL) in the retina [1]. The functional role of PSD-95 family members in photoreceptor terminals is not known. PSD-95 family members are associated with post-synaptic sites and linked to multiple anchoring/scaffold proteins [2,3]. PSD-95 family members interact with a variety of signaling and cytoskeletal proteins, including, the Shank family of proteins, which are reported to function as putative anchoring proteins for PSD-95, ionotropic and metabotropic glutamate receptors, and L-type Ca2+ channels in neurons [4,5,6,7,8]. Shank proteins consist of 3 major family members: (Shank 1-3) (Sheng and Kim 2000), and contain five domain/regions that are involved in protein-protein interactions: 1) ankyrin repeats, 2) SH3 domain, 3) PDZ domain, 4) a proline-rich region and 5) SAM domain [8].
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