Ciliogenesis is a complex multistep process used to describe assembly of cilia and flagella. These organelles play essential roles in motility and signaling on the surface of cells. Cilia are built ...at the distal ends of centrioles through the formation of an axoneme that is surrounded by the ciliary membrane. As is the case in the biogenesis of other cellular organelles, regulators of membrane trafficking play essential roles in ciliogenesis, albeit with a unique feature that membranes are organized around microtubule-based structures. Membrane association with the distal end of the centriole is a critical initiating step for ciliogenesis. Studies of this process in different cell types suggests that a singular mechanism may not be utilized to initiate cilium assembly. In this review, we focus on recent insights into cilium biogenesis and the roles membrane trafficking regulators play in described ciliogenesis mechanisms with relevance to human disease.
Membrane association with mother centriole (M-centriole) distal appendages is critical for ciliogenesis initiation. How the Rab GTPase Rab11-Rab8 cascade functions in early ciliary membrane assembly ...is unknown. Here, we show that the membrane shaping proteins EHD1 and EHD3, in association with the Rab11-Rab8 cascade, function in early ciliogenesis. EHD1 and EHD3 localize to preciliary membranes and the ciliary pocket. EHD-dependent membrane tubulation is essential for ciliary vesicle formation from smaller distal appendage vesicles (DAVs). Importantly, this step functions in M-centriole to basal body transformation and recruitment of transition zone proteins and IFT20. SNAP29, a SNARE membrane fusion regulator and EHD1-binding protein, is also required for DAV-mediated ciliary vesicle assembly. Interestingly, only after ciliary vesicle assembly is Rab8 activated for ciliary growth. Our studies uncover molecular mechanisms informing a previously uncharacterized ciliogenesis step, whereby EHD1 and EHD3 reorganize the M-centriole and associated DAVs before coordinated ciliary membrane and axoneme growth.
Proton-Coupled Electron Transfer Weinberg, David R; Gagliardi, Christopher J; Hull, Jonathan F ...
Chemical reviews,
07/2012, Letnik:
112, Številka:
7
Journal Article
Recenzirano
The importance of proton-coupled electron transfer (PCET) and its potential for practical applications in the areas of energy conversion and catalysis are discussed. PCET is bolstered by indirect ...reactions with oxygen at physically separated half reactions.
The ciliary membrane is continuous with the plasma membrane but has distinct lipid and protein composition, which is key to defining the function of the primary cilium. Ciliary membranes dynamically ...assemble and disassemble in association with the cell cycle and directly transmit signals and molecules through budding membranes. Various imaging approaches have greatly advanced the understanding of the ciliary membrane function. In particular, fluorescence live-cell imaging has revealed important insights into the dynamics of ciliary membrane assembly by monitoring the changes of fluorescent-tagged ciliary proteins. Protein dynamics can be tracked simultaneously using multi-color live cell imaging by coupling ciliary-associated factors with different colored fluorescent tags. Ciliary membrane and membrane associated-proteins such as Smoothened, 5-HTr6, SSTR3, Rab8a, and Arl13b have been used to track ciliary membranes and centriole proteins like Centrin1/2, CEP164, and CEP83 are often used to mark the ciliary basal body. Here, we describe a method for studying ciliogenesis membrane dynamics using spinning disk confocal live-cell imaging.
Sensory and signaling pathways are exquisitely organized in primary cilia. Bardet-Biedl syndrome (BBS) patients have compromised cilia and signaling. BBS proteins form the BBSome, which binds Rabin8, ...a guanine nucleotide exchange factor (GEF) activating the Rab8 GTPase, required for ciliary assembly. We now describe serum-regulated upstream vesicular transport events leading to centrosomal Rab8 activation and ciliary membrane formation. Using live microscopy imaging, we show that upon serum withdrawal Rab8 is observed to assemble the ciliary membrane in ~100 min. Rab8-dependent ciliary assembly is initiated by the relocalization of Rabin8 to Rab11-positive vesicles that are transported to the centrosome. After ciliogenesis, Rab8 ciliary transport is strongly reduced, and this reduction appears to be associated with decreased Rabin8 centrosomal accumulation. Rab11-GTP associates with the Rabin8 COOH-terminal region and is required for Rabin8 preciliary membrane trafficking to the centrosome and for ciliogenesis. Using zebrafish as a model organism, we show that Rabin8 and Rab11 are associated with the BBS pathway. Finally, using tandem affinity purification and mass spectrometry, we determined that the transport protein particle (TRAPP) II complex associates with the Rabin8 NH₂-terminal domain and show that TRAPP II subunits colocalize with centrosomal Rabin8 and are required for Rabin8 preciliary targeting and ciliogenesis.
Primary cilia are sensory organelles that utilize the compartmentalization of membrane and cytoplasm to communicate signaling events, and yet, how the formation of a cilium is coordinated with ...reorganization of the cortical membrane and cytoskeleton is unclear. Using polarized epithelia, we find that cortical actin clearing and apical membrane partitioning occur where the centrosome resides at the cell surface prior to ciliation. RAB19, a previously uncharacterized RAB, associates with the RAB-GAP TBC1D4 and the HOPS-tethering complex to coordinate cortical clearing and ciliary membrane growth, which is essential for ciliogenesis. This RAB19-directed pathway is not exclusive to polarized epithelia, as RAB19 loss in nonpolarized cell types blocks ciliogenesis with a docked ciliary vesicle. Remarkably, inhibiting actomyosin contractility can substitute for the function of the RAB19 complex and restore ciliogenesis in knockout cells. Together, this work provides a mechanistic understanding behind a cytoskeletal clearing and membrane partitioning step required for ciliogenesis.
Correlative light and electron microscopy (CLEM) enables determination of high-resolution structural information for proteins of interest within their biological context through the combination of ...electron and fluorescence microscopies. Numerous electron microscopy (EM) studies of primary cilia have provided ultrastructural details about these antennal-like organelles that extend from the surface of the cell. The core structure of the cilium includes a microtubule-based axoneme, a basal body derived from the mother centriole, and the ciliary membrane, which is connected to the plasma membrane. The small GTPase Rab8 localizes to the ciliary membrane and is important for ciliogenesis, and Rab11 transports the Rab8 guanine nucleotide exchange factor (GEF) Rabin8 to the mother centriole to activate Rab8-dependent ciliary membrane growth. Some primary cilia have a ciliary pocket membrane (CPM) which is observed as an involution from the plasma membrane to the base of the cilia membrane. The Rab11- and Rab8-assocaited membrane trafficking regulator Eps15 Homology Domain-containing protein 1 (EHD1) and EHD3 also function in early stages of ciliogenesis; however, they localize to the CPM. These ciliary localizations of Rab8 and EHD1 can be resolved using CLEM with conventional fluorescence microscopy and transmission electron microscopy (TEM) imaging. Here, we describe in detail the protocol for this CLEM method applicable for ciliary proteins and proteins in other cellular organelles.
Mutations in CEP290, a transition zone protein in primary cilia, cause diverse ciliopathies, including Leber congenital amaurosis (LCA) and Joubert-syndrome and related disorders (JSRD). We examined ...cilia biogenesis and function in cells derived from CEP290-LCA and CEP290-JSRD patients. CEP290 protein was reduced in LCA fibroblasts with no detectable impact on cilia; however, optic cups derived from induced pluripotent stem cells (iPSCs) of CEP290-LCA patients displayed less developed photoreceptor cilia. Lack of CEP290 in JSRD fibroblasts resulted in abnormal cilia and decreased ciliogenesis. We observed selectively reduced localization of ADCY3 and ARL13B. Notably, Hedgehog signaling was augmented in CEP290-JSRD because of enhanced ciliary transport of Smoothened and GPR161. These results demonstrate a direct correlation between the extent of ciliogenesis defects in fibroblasts and photoreceptors with phenotypic severity in JSRD and LCA, respectively, and strengthen the role of CEP290 as a selective ciliary gatekeeper for transport of signaling molecules in and out of the cilium.
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•Normal cilia in fibroblasts, but not in photoreceptors of CEP290-LCA organoids•No CEP290 protein and defective ciliogenesis in CEP290-JSRD fibroblasts•Selective reduction in ciliary localization of ARL13B and ADCY3 in JSRD fibroblasts•Cilia defects in JSRD fibroblasts affect Smo and GPR161 transport in Hh signaling
Using fibroblasts and iPSC-derived optic cups from patients with distinct CEP290 mutations, Shimada et al. show a concordance between ciliogenesis defects in different cell types and clinical severity in Leber congenital amaurosis and Joubert syndrome. These studies establish CEP290 as gatekeeper of signaling molecules in and out of the primary cilium.
Airway multiciliated epithelial cells play crucial roles in the mucosal defense system, but their differentiation process remains poorly understood. Mice lacking the basal body component Chibby (Cby) ...exhibit impaired mucociliary transport caused by defective ciliogenesis, resulting in chronic airway infection. In this paper, using primary cultures of mouse tracheal epithelial cells, we show that Cby facilitates basal body docking to the apical cell membrane through proper formation of ciliary vesicles at the distal appendage during the early stages of ciliogenesis. Cby is recruited to the distal appendages of centrioles via physical interaction with the distal appendage protein CEP164. Cby then associates with the membrane trafficking machinery component Rabin8, a guanine nucleotide exchange factor for the small guanosine triphosphatase Rab8, to promote recruitment of Rab8 and efficient assembly of ciliary vesicles. Thus, our study identifies Cby as a key regulator of ciliary vesicle formation and basal body docking during the differentiation of airway ciliated cells.
Objectives. Patients with RA have an increased prevalence of cardiovascular disease (CVD). This is due to traditional risk factors and the effects of chronic inflammation. MTX is the first-choice ...DMARD in RA. We performed a systematic literature review to determine whether MTX affects the risk of CVD in patients with RA. Methods. We searched Medline, Embase, Cochrane database, database of abstracts of reviews of effects, health technology assessment and Science Citation Index from 1980 to 2008. Conference proceedings (British Society of Rheumatology, ACR and EULAR) were searched from 2005 to 2008. Papers were included if they assessed the relationship between MTX use and CVD in patients with RA. Two reviewers independently assessed each title and abstract for relevance and quality. Results. A total of 2420 abstracts were identified, of which 18 fulfilled the inclusion criteria. Two studies assessed the relationship between MTX use and CVD mortality, one demonstrated a significant reduction in CVD mortality and the second a trend towards reduction. Five studies considered all-cause CVD morbidity. Four demonstrated a significant reduction in CVD morbidity and the fifth a trend towards reduction. MTX use in the year prior to the development of RA decreased the risk of CVD for 3−4 years. Four studies considered myocardial infarction, one demonstrated a decreased risk and three a trend towards decreased risk with MTX use. Conclusion. The current evidence suggests that MTX use is associated with a reduced risk of CVD events in patients with RA. This suggests that reducing the inflammation in RA using MTX not only improves disease-specific outcomes but may also reduce collateral damage such as atherosclerosis.
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