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U. Wolfrum, M. Latz, G. J. Pazour, T. Sedmak; Differential Ciliary and Non-Ciliary Localization of IFT Molecules in the Mammalian Retina. Invest. Ophthalmol. Vis. Sci. 2009;50(13):2714.
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© ARVO (1962-2015); The Authors (2016-present)
For the maintenance and function of vertebrate photoreceptor cells directed transport mechanisms are essential. Intraflagellar transport (IFT) has been proposed as an essential mechanism for the delivery of components to and from the outer segment of photoreceptor cells. It comprises the bidirectional transport of IFT particles containing cargo along the ciliary microtubules mediated by molecular motors. Although, it is known that IFT particles are composed of at least 16 individual IFT proteins (IFTs), their precise role in IFT remained so far elusive. Knowledge of the precise spatial distribution of IFTs in the retinal photoreceptor cells should provide valuable novel insights in the cellular function of IFTs and photoreceptor cell biology.
We studied the subcellular localization of individual IFTs, namely IFT20, 52, 57, 88, and 140 in the mouse retina using a combination of high resolution immunofluorescence and immunoelectron microscopy.
All IFTs investigated were expressed in the ciliated photoreceptor cells of the mouse retina. The IFTs were differential localized in sub-compartments of the photoreceptor ciliary apparatus; some IFTs appear in the axoneme in the outer segment and in different parts of the connecting cilium, all were highly concentrated at the periciliary region around the basal body within the inner segment where they were associated with transport vesicles. IFT20 was additionally associated with the Golgi in the photoreceptor inner segment. Furthermore, a set of IFTs, IFT20, 52, and 57, were localized in the outer plexiform layer where the synapses between photoreceptor cells and 2nd neurons. Surprisingly, these IFTs were not present in the photoreceptor cell terminals, but localized in the post-synaptic compartment and in the dendritic processes of non-ciliated horizontal and bipolar cells.
Our present data shine new light on intracellular transport mechanisms in photoreceptor cells and 2nd retinal neurons. Differential localization of IFTs in photoreceptor cell compartments indicates roles of IFTs in the different transport modules for the delivery of cargo to and from the outer segment. Furthermore, the dendritic expression of IFTs provides evidence for cellular functions of IFTs other than ciliary function.
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