During ciliogenesis, this basal body is positioned close to the plasma membrane and ciliary microtubules elongate from its distal end. indispensable for PC formation and hence characterized in detail. By immunogold electron microscopy, PROTAC MDM2 Degrader-4 Cep164 could be localized to the distal appendages of mature centrioles. In contrast to ninein and Cep170, two components of subdistal appendages, Cep164 persisted at centrioles throughout mitosis. Moreover, the localizations of Cep164 and ninein/Cep170 were mutually impartial during interphase. These data implicate distal appendages in PC formation and identify Cep164 as an excellent marker for these structures. Introduction The primary cilium (PC) is usually a microtubule-based structure that protrudes from the surface of most vertebrate cells. It generally comprises a membrane-bound 9 + 0 ciliary axoneme, which consists of nine outer doublet microtubules but lacks both the central microtubule pair and dynein arms. Thus, with few exceptions, PC are nonmotile and instead function as sensory organelles (Pazour and Witman, 2003; Singla and Reiter, 2006; Satir and Christensen, 2007). FGF5 They play important roles during development, particularly with regard to the establishment of leftCright asymmetry, as well as later in life when they are required for the processing of mechanical or chemical signals in many organs (Iba?ez-Tallon et al., 2003; Praetorius and Spring, 2005). For instance, in PROTAC MDM2 Degrader-4 kidney epithelial cells, PC sense fluids circulation within the lumen of the nephron, which is critical for normal epithelial development and function. Proteins localizing to the ciliary membrane, known as polycystins, play an important role in mediating this mechanosensory function, and mutations in the corresponding genes cause polycystic kidney disease (Boucher and Sandford, 2004). Similarly, retinal degeneration can be caused by dysfunction of the connecting cilium, a highly specialized PC connecting the inner and outer segments in vertebrate photoreceptors (Badano et al., 2006; Singla and Reiter, 2006). Moreover, recent studies implicate PC in various transmission transduction pathways, including sonic hedgehog, platelet-derived growth factor receptor , and Wnt signaling (Singla and Reiter, 2006; Satir and Christensen, 2007). Ciliary defects have also been causally linked to several pleiotropic disorders, including Bardet-Biedl syndrome (BBS), Alstrom syndrome (ALMS), oral-facial-digital syndrome type I, and nephronophthisis (Badano et al., 2006; Hildebrandt and Zhou, 2007; Zariwala et al., 2007). The assembly of the PC requires a basal body, which in turn is derived from one of the two centrioles that constitute the centrosome. During ciliogenesis, this basal body is positioned close to the plasma membrane and ciliary microtubules elongate from its distal end. Ciliogenesis requires the assembly of multiple soluble and membranous protein complexes. In particular, the so-called intraflagellar transport (IFT) system is then responsible for moving cargo (IFT particles) to and from the tip of the growing axoneme. IFT, first described in the algae (Kozminski et al., 1993), is now known to be mediated by the association of IFT particles with kinesin II and dynein microtubuleCbased motors for antero- and retrograde movement, respectively (Rosenbaum and Witman, 2002; Scholey, 2003). The signaling networks that control PC function during cell cycle progression remain to be elucidated, but several studies concur to identify a key role for the von Hippel-Lindau tumor suppressor in PC formation (Lutz and Burk, 2006; Schermer et al., 2006; Thoma et al., 2007). Furthermore, Aurora A kinase has recently been implicated in PC resorption (Pugacheva et al., 2007). In this study, we have sought to identify centrosomal proteins (Ceps) that are required for ciliogenesis. Taking advantage of the fact that PC formation can be induced in cultured cells by serum starvation (Tucker et al., 1979; Vorobjev and Chentsov, 1982), we depleted individual centrosomal proteins by PROTAC MDM2 Degrader-4 PROTAC MDM2 Degrader-4 siRNA and examined the consequences on subsequent PC formation. This siRNA screen identified several proteins that affected PC formation, albeit PROTAC MDM2 Degrader-4 to different degrees. A very strong effect was observed upon depletion of Cep164, a protein that had not previously been studied. Our characterization of Cep164 leads to conclude that this protein is not only required for PC formation but also constitutes an excellent marker for distal appendages on mature centrioles or basal bodies. Results Identification of centrosomal proteins involved in PC formation To search for proteins involved in PC formation, an siRNA screen focusing on centrosomal proteins (Andersen et al., 2003) was performed. After the depletion of individual proteins from retinal pigment epithelial (hTERT-RPE1) cells, PC formation was induced by serum starvation (Vorobjev and Chentsov, 1982) and monitored by staining with antibodies against acetylated tubulin (Piperno and Fuller, 1985). Depletion efficiency was assessed by quantitative real-time PCR (qRT-PCR) and, whenever possible, immunofluorescence (IF) microscopy and/or Western blot analysis (Table S1, available at http://www.jcb.org/cgi/content/full/jcb.200707181/DC1). Because depletion.
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