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Uwe Wolfrum, Tina Sedmak; Intraflagelar Transport Proteins In Ciliogenesis Of Photoreceptor Cells. Invest. Ophthalmol. Vis. Sci. 2011;52(14):4405.
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Assembly and maintenance of cilia dependent on the intraflagellar transport (IFT) mediated by molecular motors and their interaction with specific IFT proteins. Here the participation of IFT in the ciliogenesis of mammalian photoreceptor cilia was investigated.
We studied the spacial distribution of IFT proteins by correlative immunofluorescense and electron microscopy.
Electron microscopy revealed that in contrast to previous reports the photoreceptor cilium is formed in an intracellular pathway. Based on our observations we divided the ciliogenesis in photoreceptors in 6 distinct district stages. The first stages are characterized by electron dense centriolar satellites and the ciliary vesicle enclosing the elongating ciliary shaft of evolving primary cilium. In later ciliogenesis, when the growing cilium protrudes into the extracellular space, the proximal ciliary shaft remodels into the connecting cilium, whereas the distal forms the outer segment. During photoreceptor differentiation IFT proteins are associated with the ciliary apparatus in all defined stages of ciliogenesis. Correlative high resolution microscopy analysis revealed that in addition to the centriole and basal body, IFT proteins are localized in the cytoplasm, associated with the centriolar satellites, post-Golgi vesicles and the surface of the ciliary vesicle. Later in ciliogenesis, the localization patterns of most IFT molecules correspond to mature distribution.
We provide evidence for the participation of IFT proteins in photoreceptor ciliogenesis, namely in the formation of the ciliary vesicle and the elongation of the primary cilium. In advanced stages of ciliogenesis the ciliary localization of IFT proteins indicate their role in IFT as seen in mature cilia. The accumulation of IFT proteins in the pericliary cytoplasm at the ciliary base probably resembles an IFT molecule pool waiting in the wings for the delivery into the growing ciliary shaft. Nevertheless, cytoplasmic IFT proteins not related to the ciliary shaft indicate roles of IFT proteins beyond its well established function for IFT.
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