Intraflagellar transport proteins in ciliogenesis of photoreceptor cells

Abstract

Background information. The assembly and maintenance of cilia depend on IFT (intraflagellar transport) mediated by molecular motors and their interplay with IFT proteins. Here, we have analysed the involvement of IFT proteins in the ciliogenesis of mammalian photoreceptor cilia.Results. Electron microscopy revealed that ciliogenesis in mouse photoreceptor cells follows an intracellular ciliogenesis pathway, divided into six distinct stages. The first stages are characterized by electron-dense centriolar satellites and a ciliary vesicle, whereas the formations of the ciliary shaft and the light-sensitive outer segment discs are features of the later stages. IFT proteins were associated with ciliary apparatus during all stages of photoreceptor cell development.Conclusions. Our data conclusively provide evidence for the participation of IFT proteins in photoreceptor cell ciliogenesis, including the formation of the ciliary vesicle and the elongation of the primary cilium. In advanced stages of ciliogenesis the ciliary localization of IFT proteins indicates a role in IFT as is seen in mature cilia. A prominent accumulation of IFT proteins in the periciliary cytoplasm at the base of the cilia in these stages most probably resembles a reserve pool of IFT molecules for further delivery into the growing ciliary shaft and their subsequent function in IFT. Nevertheless, the cytoplasmic localization of IFT proteins in the absence of a ciliary shaft in early stages of ciliogenesis may indicate roles of IFT proteins beyond their well-established function for IFT in mature cilia and flagella.

The role of primary cilia in the development and disease of the retina

“…27 Refer to Table S1 for further details. Photoreceptor biogenesis has been suggested to occur in six distinct stages, 28 based on the four phases of ciliogenesis in an epithelial cell, 29 followed by two stages of OS development. This whole process takes over two weeks to complete in the mouse retina.…”

“…A pool of IFT proteins is localized in the cytoplasm at the base of the axoneme during the formation of the ciliary vesicle and elongation of the axoneme early in CC and OS development, and IFT proteins are consistently associated with the developed axoneme. 28 IFT is also essential for normal photoreceptor function by mediating the transport of proteins of the phototransduction cascade to the OS. 87 Cargoes of IFT have been shown to include rhodopsin, chaperone proteins and the photoreceptor-specific membrane protein guanylyl cyclase 1 (GC1, Gucy2e).…”

“…This ciliary vesicle then fuses with the plasma membrane and the CC extends toward the RPE. 28,42 The protein CC2D2A plays a role in extension of the CC membrane through RAB8-mediated vesicular trafficking. cc2d2a zebrafish morphants develop disorganized photoreceptor OS and accumulation of opsins and vesicles in IS.…”

Germline deletion of Cetn1 causes infertility in male mice

“…Dissected testes were fixed in cacodylate-buffered glutaraldehyde and osmium tetroxide followed by RenlamH M-1 resin (Serva, Heidelberg, Germany) as described (Sedmak and Wolfrum, 2011). Semi thin sections (1 mm thick) were cut, contrasted with methylene blue and azure B, and viewed with a Leica DM 6000B microscope (Leica Microsystems, Bensheim, Germany).…”

Ciliopathy proteins establish a bipartite signaling compartment in aC. elegansthermosensory neuron

“…This multimeric assembly functions with the small GTPase BBS3/ARL6 as a membrane-associated coat involved in trafficking ciliary cargoes (Jin et al, 2010). BBS proteins associate with the intraflagellar transport (IFT) machinery (Blacque et al, 2004;Ou et al, 2005;Ou et al, 2007), which uses motor proteins and accessory complexes to build and functionally maintain cilia (Silverman and Leroux, 2009;Sedmak and Wolfrum, 2011;Sung and Leroux, 2013). Signaling components that require BBS proteins for trafficking into (or out of) cilia include GPCR proteins, such as melanin-concentrating hormone receptor 1 (MCHR1), somatostatin receptor type 3 (SSTR3), dopamine receptor type 1 (D1) and rhodopsin (Nishimura et al, 2004;Berbari et al, 2008;Domire et al, 2011).…”