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R. Wudali, G. Daly, G.W. Balkema, D.D. Hunter, W.J. Brunken; Sub–Cellular Localization of Adhesion Proteins at the Photoreceptor Synaptic Terminal . Invest. Ophthalmol. Vis. Sci. 2006;47(13):151.
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The exact composition, function and modes of anchorage of synaptic ribbons in the photoreceptor terminal are not known. Recent studies using genetic manipulations in mice suggest that bassoon (Dick et al 2003) and laminins (Libby et al 1999) are critical elements for anchoring synaptic ribbons and maintaining normal synaptic function. The purpose of this study is to determine what elements of the cytomatrix might serve to anchor the synaptic ribbon in the photoreceptor terminal. The presence in photoreceptor terminals of receptors related to an epithelial adhesion complex (Claudepierre et al, '05) led us to search for elements of adhesion complexes at this synapse.
Retinae were collected from wild type (C57BL/6J) adult mice and were fixed in 4% para–formaldehyde, embedded in OCT and sectioned for immunohistochemical studies. The presence of α–actinin, talin, focal adhesion kinase (FAK), proline rich tyrosine kinase2 (PYK2) and paxillin was examined in photoreceptor synapses; Bassoon and piccolo were used as markers of the ribbon; calbindin and α–PKC were used to mark post–synaptic dendrites.
As predicted, cytomatrix–associated elements were associated with synaptic structures; specifically, α–actinin, talin, paxillin, FAK and PYK2 all were present both in outer and inner plexiform layers. Somewhat surprisingly, α–actinin appears to be distributed on the post–synaptic side of the synapse, as it co–localized with calbindin and α–PKC, markers of horizontal and bipolar cell respectively. Limited overlap with bassoon, a synaptic ribbon protein, was seen. On the other hand, talin and paxillin showed extensive co–localization with the ribbon protein, piccolo, suggesting that these molecules are elements used to anchor the ribbon. Similarly, FAK and PYK2 were co–distributed presynaptically with bassoon. Currently, biochemical methods are underway to determine the molecular interactions among these molecules.
These results indicate that indeed elements of epithelial adhesion complexes are present at the photoreceptor synapse and may play an important role in anchoring the ribbon and thereby promoting synaptic transmission.
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