scholarly journals NPHP proteins: gatekeepers of the ciliary compartment

2010 ◽  
Vol 190 (5) ◽  
pp. 715-717 ◽  
Author(s):  
Heymut Omran
Keyword(s):  
Chlamydomonas Reinhardtii ◽  
Transition Zone ◽  
Structural Integrity ◽  
Ciliary Membrane ◽  
Integral Component ◽  
Cell Biol

The cilia and the cytoplasm are separated by a region called the transition zone, where wedge-shaped structures link the microtubule doublets of the axoneme to the ciliary membrane, thereby forming a ciliary “gate.” In this issue, Craige et al. (J. Cell Biol. doi:10.1083/jcb.201006105) demonstrate in Chlamydomonas reinhardtii that Nphp6/cep290, which is mutated in nephronophthisis (NPHP), is an integral component of these connectors and maintains the structural integrity of this gate.

scholarly journals Centrin plays an essential role in microtubule severing during flagellar excision in Chlamydomonas reinhardtii

1994 ◽  
Vol 124 (5) ◽  
pp. 795-805 ◽  
Author(s):  
MA Sanders ◽  
JL Salisbury
Keyword(s):  
Chlamydomonas Reinhardtii ◽  
Transition Zone ◽  
Cell Model ◽  
Inhibitory Effect ◽  
Free Calcium ◽  
Cell Models ◽  
Microtubule Severing ◽  
Cell Biol ◽  
Molecular Machinery ◽  
D Cells

Previously, we reported that flagellar excision in Chlamydomonas reinhardtii is mediated by an active process whereby microtubules are severed at select sites within the flagellar-basal body transition zone (Sanders, M. A., and J. L. Salisbury. 1989. J. Cell Biol. 108:1751-1760). At the time of flagellar excision, stellate fibers of the transition zone contract and displace the microtubule doublets of the axoneme inward. The resulting shear force and torsional load generated during inward displacement leads to microtubule severing immediately distal to the central cylinder of the transition zone. In this study, we have used a detergent-extracted cell model of Chlamydomonas that allows direct experimental access to the molecular machinery responsible for microtubule severing without the impediment of the plasma membrane. We present four independent lines of experimental evidence for the essential involvement of centrin-based stellate fibers of the transition zone in the process of flagellar excision: (a) Detergent-extracted cell models excise their flagella in response to elevated, yet physiological, levels of free calcium. (b) Extraction of cell models with buffers containing the divalent cation chelator EDTA leads to the disassembly of centrin-based fibers and to the disruption of transition zone stellate fiber structure. This treatment results in a complete loss of flagellar excision competence. (c) Three separate anti-centrin monoclonal antibody preparations, which localize to the stellate fibers of the transition zone, specifically inhibit contraction of the stellate fibers and block calcium-induced flagellar excision, while control antibodies have no inhibitory effect. Finally, (d) cells of the centrin mutant vfl-2 (Taillon, B., S. Adler, J. Suhan, and J. Jarvik. 1992. J. Cell Biol. 119:1613-1624) fail to actively excise their flagella following pH shock in living cells or calcium treatment of detergent-extracted cell models. Taken together, these observations demonstrate that centrin-based fiber contraction plays a fundamental role in microtubule severing at the time of flagellar excision in Chlamydomonas.

scholarly journals Mapping the assembly pathways that specify formation of the trilaminar kinetochore plates in human cells

2006 ◽  
Vol 175 (1) ◽  
pp. 41-53 ◽  
Author(s):  
Song-Tao Liu ◽  
Jerome B. Rattner ◽  
Sandra A. Jablonski ◽  
Tim J. Yen
Keyword(s):  
Hela Cells ◽  
Structural Integrity ◽  
Human Cells ◽  
Previous Model ◽  
Aurora B ◽  
Assembly Process ◽  
Centromere Protein ◽  
Cell Biol ◽  
Assembly Pathways

We report the interactions amongst 20 proteins that specify their assembly to the centromere–kinetochore complex in human cells. Centromere protein (CENP)-A is at the top of a hierarchy that directs three major pathways, which are specified by CENP-C, -I, and Aurora B. Each pathway consists of branches that intersect to form nodes that may coordinate the assembly process. Complementary EM studies found that the formation of kinetochore trilaminar plates depends on the CENP-I/NUF2 branch, whereas CENP-C and Aurora B affect the size, shape, and structural integrity of the plates. We found that hMis12 is not constitutively localized at kinetochores, and that it is not essential for recruiting CENP-I. Our studies also revealed that kinetochores in HeLa cells contain an excess of CENP-A, of which ∼10% is sufficient to promote the assembly of normal levels of kinetochore proteins. We elaborate on a previous model that suggested kinetochores are assembled from repetitive modules (Zinkowski, R.P., J. Meyne, and B.R. Brinkley. 1991. J. Cell Biol. 113:1091–110).

scholarly journals Two distinct, calcium-mediated, signal transduction pathways can trigger deflagellation in Chlamydomonas reinhardtii

1994 ◽  
Vol 124 (5) ◽  
pp. 807-815 ◽  
Author(s):  
LM Quarmby ◽  
HC Hartzell
Keyword(s):  
Signal Transduction ◽  
Chlamydomonas Reinhardtii ◽  
Living Cells ◽  
Signalling Pathways ◽  
Signal Transduction Pathways ◽  
Channel Blockers ◽  
Wasp Venom ◽  
Intracellular Pool ◽  
Cell Biol ◽  
Molecular Machinery

The molecular machinery of deflagellation can be activated in detergent permeabilized Chlamydomonas reinhardtii by the addition of Ca2+ (Sanders, M. A., and J. L. Salisbury, 1989. J. Cell Biol. 108:1751-1760). This suggests that stimuli which induce deflagellation in living cells cause an increase in the intracellular concentration of Ca2+, but this has never been demonstrated. In this paper we report that the wasp venom peptide, mastoparan, and the permeant organic acid, benzoate, activate two different signalling pathways to trigger deflagellation. We have characterized each pathway with respect to: (a) the requirement for extracellular Ca2+; (b) sensitivity to Ca2+ channel blockers; and (c) 45Ca influx. We also report that a new mutant strain of C. reinhardtii, adf-1, is specifically defective in the acid-activated signalling pathway. Both signalling pathways appear normal in another mutant, fa-1, that is defective in the machinery of deflagellation (Lewin, R. and C. Burrascano. 1983. Experientia. 39:1397-1398; Sanders, M. A., and J. L. Salisbury. 1989. J. Cell Biol. 108:1751-1760). We conclude that mastoparan induces the release of an intracellular pool of Ca2+ whereas acid induces an influx of extracellular Ca2+ to activate the machinery of deflagellation.

scholarly journals Electron Cryo-Tomography Provides Insight into Procentriole Architecture and Assembly Mechanism

2018 ◽  
Author(s):  
Sam Li ◽  
Jose-Jesus Fernandez ◽  
Wallace F. Marshall ◽  
David A. Agard
Keyword(s):  
Chlamydomonas Reinhardtii ◽  
Molecular Mechanisms ◽  
Longitudinal Direction ◽  
Multiple Functions ◽  
Iris Diaphragm ◽  
Cellular Processes ◽  
Structural Framework ◽  
Integral Component ◽  
Assembly Mechanism ◽  
Insight Into

SummaryCentriole is an essential structure with multiple functions in cellular processes. Centriole biogenesis and homeostasis is tightly regulated. Using electron cryo-tomography (cryoET) we present the structure of procentrioles from Chlamydomonas reinhardtii. We identified a set of non-tubulin components attached to the triplet microtubule (MT), many are at the junctions of tubules likely to reinforce the triplet. We describe structure of the A-C linker that bridges neighboring triplets. We find that POC1 is an integral component of the A-C linker. Its conserved WD40 β-propeller domain provides sites for attachment to other A-C linker components. The twist of A-C linker results in an iris diaphragm-like motion of the triplets in the longitudinal direction of procentriole. Finally, we identified two assembly intermediates at the growing ends of procentriole allowing us to propose a model for the procentriole assembly. Our results provide a comprehensive structural framework for understanding the molecular mechanisms underpinning procentriole biogenesis and assembly.

scholarly journals ARL3 Mediates BBSome Ciliary Turnover by Promoting Its Outward Diffusion through the Transition Zone

2021 ◽  
Author(s):  
Yan-Xia Liu ◽  
Wei-Yue Sun ◽  
Bin Xue ◽  
Rui-Kai Zhang ◽  
Wen-Juan Li ◽  
...  
Keyword(s):  
Transition Zone ◽  
Phospholipase D ◽  
Physiological Condition ◽  
Intraflagellar Transport ◽  
Outward Diffusion ◽  
Ciliary Membrane ◽  
Downstream Signaling ◽  
Extracellular Stimuli ◽  
Signaling Components ◽  
Ciliary Signaling

Ciliary receptors and their certain downstream signaling components undergo intraflagellar transport (IFT) as BBSome cargoes to maintain their ciliary dynamics for sensing and transducing extracellular stimuli inside the cell. Cargo laden BBSomes shed from retrograde IFT at the proximal ciliary region above the transition zone (TZ) followed by diffusing through the TZ for ciliary retrieval, while how the BBSome barrier passage is controlled remains elusive. Here, we show that the BBSome is a major effector of the Arf-like 3 (ARL3) GTPase in Chlamydomonas. Under physiological condition, ARL3GDP binds the membrane for diffusing into and residing in cilia. Following a nucleotide conversion, ARL3GTP dissociates with the ciliary membrane and binds and recruits the IFT-detached and cargo (phospholipase D, PLD)-laden BBSome at the proximal ciliary region to diffuse through the TZ and out of cilia. ARL3 deficiency impairs ciliary signaling, e.g. phototaxis of Chlamydomonas cells, by disrupting BBSome ciliary retrieval, providing a mechanistic understanding behind BBSome ciliary turnover required for ciliary signaling.

ESCRT subunit CHMP4B localizes to primary cilia and is required for the structural integrity of the ciliary membrane

2019 ◽  
Vol 34 (1) ◽  
pp. 1331-1344 ◽  
Author(s):  
Eunji Jung ◽  
Tae‐Ik Choi ◽  
Ji‐Eun Lee ◽  
Cheol‐Hee Kim ◽  
Joon Kim
Keyword(s):  
Primary Cilia ◽  
Structural Integrity ◽  
Ciliary Membrane

scholarly journals Formation of the B9-domain protein complex MKS1–B9D2–B9D1 is essential as a diffusion barrier for ciliary membrane proteins

2020 ◽  
Vol 31 (20) ◽  
pp. 2259-2268
Author(s):  
Misato Okazaki ◽  
Takuya Kobayashi ◽  
Shuhei Chiba ◽  
Ryota Takei ◽  
Luxiaoxue Liang ◽  
...  
Keyword(s):  
Membrane Proteins ◽  
Transition Zone ◽  
Diffusion Barrier ◽  
Protein Complex ◽  
Ciliary Membrane ◽  
Meckel Syndrome ◽  
Interaction Mode ◽  
Domain Protein

Meckel syndrome (MKS)1, B9 domain (B9D)1, and B9D2 are soluble transition zone (TZ) proteins and share a B9D. We demonstrate the interaction mode of these B9D proteins to be MKS1-B9D2-B9D1 and their interdependent localization to the TZ. We also show that formation of the B9D protein complex is crucial for creating a diffusion barrier for ciliary membrane proteins.

scholarly journals A transition zone complex regulates mammalian ciliogenesis and ciliary membrane composition

2011 ◽  
Vol 43 (8) ◽  
pp. 776-784 ◽  
Author(s):  
Francesc R Garcia-Gonzalo ◽  
Kevin C Corbit ◽  
María Salomé Sirerol-Piquer ◽  
Gokul Ramaswami ◽  
Edgar A Otto ◽  
...  
Keyword(s):  
Transition Zone ◽  
Membrane Composition ◽  
Ciliary Membrane

scholarly journals A solid-state control system for dynein-based ciliary/flagellar motility

2013 ◽  
Vol 201 (2) ◽  
pp. 173-175 ◽  
Author(s):  
Stephen M. King
Keyword(s):  
Control System ◽  
Solid State ◽  
Chlamydomonas Reinhardtii ◽  
State Control ◽  
Flagellar Motility ◽  
Regulatory Structure ◽  
Coordinated Action ◽  
Cell Biol ◽  
Radial Spokes

Ciliary and flagellar beating requires the coordinated action of multiple dyneins with different enzymatic and motor properties. In this issue, Yamamoto et al. (2013. J. Cell Biol. http://dx.doi.org/10.1083/jcb.201211048) identify the MIA (modifier of inner arms) complex within the Chlamydomonas reinhardtii axoneme that physically links to a known regulatory structure and provides a signaling conduit from the radial spokes to an inner arm dynein essential for waveform determination.

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