A size-exclusion permeability barrier and nucleoporins characterize a ciliary pore complex that regulates transport into cilia

Kee, Hooi Lynn; Dishinger, John F.; Blasius, T. Lynne; Liu, Chia Jen; Margolis, Ben; Verhey, Kristen J.

doi:10.1038/ncb2450

Cited by 292 publications

(359 citation statements)

References 39 publications

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“…4D). Given the similarities between ciliary and nuclear import (4,37,38), we expect that avalanche-like behavior also may have relevance to the study of nuclear import dynamics (39)(40)(41). Our data show that IFT exhibits avalanche-like qualities, indicating that some of the fundamental organization of cells is in fact self-organizing.…”

Section: Discussionmentioning

confidence: 74%

Avalanche-like behavior in ciliary import

Ludington

Wemmer

Lechtreck

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

118

201

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Cilia and flagella are microtubule-based organelles that protrude from the cell body. Ciliary assembly requires intraflagellar transport (IFT), a motile system that delivers cargo from the cell body to the flagellar tip for assembly. The process controlling injections of IFT proteins into the flagellar compartment is, therefore, crucial to ciliogenesis. Extensive biochemical and genetic analyses have determined the molecular machinery of IFT, but these studies do not explain what regulates IFT injection rate. Here, we provide evidence that IFT injections result from avalanche-like releases of accumulated IFT material at the flagellar base and that the key regulated feature of length control is the recruitment of IFT material to the flagellar base. We used total internal reflection fluorescence microscopy of IFT proteins in live cells to quantify the size and frequency of injections over time. The injection dynamics reveal a power-law tailed distribution of injection event sizes and a negative correlation between injection size and frequency, as well as rich behaviors such as quasiperiodicity, bursting, and long-memory effects tied to the size of the localized load of IFT material awaiting injection at the flagellar base, collectively indicating that IFT injection dynamics result from avalanche-like behavior. Computational models based on avalanching recapitulate observed IFT dynamics, and we further show that the flagellar Ras-related nuclear protein (Ran) guanosine 5'-triphosphate (GTP) gradient can in theory act as a flagellar length sensor to regulate this localized accumulation of IFT. These results demonstrate that a self-organizing, physical mechanism can control a biochemically complex intracellular transport pathway.Chlamydomonas | self-organization | nuclear import | long flagella mutants | power spectrum C ilia and flagella generate fluid flows and mediate cell signaling (1), and ciliary length defects cause a wide range of congenital human diseases. Many of these defects arise from mutations in intraflagellar transport (IFT) proteins, which are required to build and maintain the length of cilia and flagella (2). The IFT proteins form complexes called IFT trains that haul cargo to the ciliary tip for assembly (3-7). IFT trains first localize to the basal body (8) and then enter the cilium as a group in an injection event. Understanding the IFT injection process is critical to understanding ciliary length control because the injection rate sets the overall amount of transport that in turn determines the rate of steadystate flagellar assembly (9).A previous report indicated that entry of new IFT trains is periodic (10), suggesting that a biochemical oscillator may regulate IFT injection. However, the biochemical components of this hypothetical oscillator are currently unknown. Components of the gate controlling entry into the cilium are being identified (4, 5), but identifying the oscillating components themselves could be an extremely difficult biochemical problem because it is not obvious how to determ...

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Section: Discussionmentioning

confidence: 74%

Avalanche-like behavior in ciliary import

Ludington

Wemmer

Lechtreck

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

118

201

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“…15 This complex is a highly organized structure molecularly similar to the nuclear pore, where different precursors and intraflagellar transport (IFT) proteins, along with proteins of different signaling pathways, are selected and concentrated before entering the axoneme. 16 Continuous trafficking of cargo molecules along the ciliary axoneme is controlled by the evolutionarily conserved IFT mechanism. 17 Trafficking along the axoneme is maintained through the action of two motor protein families: kinesins, responsible for anterograde IFT, and dyneins, responsible for retrograde IFT.…”

Section: Cilium: Structure and Signalingmentioning

confidence: 99%

Autophagy and regulation of cilia function and assembly

et al. 2014

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Motile and primary cilia (PC) are microtubule-based structures located at the cell surface of many cell types. Cilia govern cellular functions ranging from motility to integration of mechanical and chemical signaling from the environment. Recent studies highlight the interplay between cilia and autophagy, a conserved cellular process responsible for intracellular degradation. Signaling from the PC recruits the autophagic machinery to trigger autophagosome formation. Conversely, autophagy regulates ciliogenesis by controlling the levels of ciliary proteins. The cross talk between autophagy and ciliated structures is a novel aspect of cell biology with major implications in development, physiology and human pathologies related to defects in cilium function. Cell Death and Differentiation (2015) 22, 389-397; doi:10.1038/cdd.2014.171; published online 31 October 2014 FactsAutophagy is a degradative and recycling mechanism that allows cells to adapt to stress situations including nutrient deprivation. Primary cilia (PC) and motile cilia (MC) are sensory structures at the cell surface. PC sense nutrient, growth factor and calcium changes in the extracellular environment and also respond to mechanical stress. MC are beating structures that contribute to innate defense in the lung, for example. The PC is a site for the recruitment of autophagy-related (ATG) proteins that mediate autophagosome formation in response to cilium-dependent signaling. In turn, autophagy regulates the biogenesis of cilia by degrading certain proteins involved in cilia formation. Modulation of autophagy represents a new therapeutic opportunity in diseases related to defective cilia function. Open QuestionsHow are ATG proteins transported to the PC? How do ATG proteins recruited to the PC contribute to the biogenesis of phagophores and autophagosomes? Ciliary proteins are degraded by autophagy. How selective is this degradative pathway? Do some of these proteins contain motifs that result in selective engulfment by autophagosomes?What are the determinants that switch the degradation of ciliary proteins between basal and induced autophagy? Is there any specific function for cilium-dependent autophagy in ciliated cells? Do signals that trigger cilium-dependent autophagy depend on the stimuli (chemical, mechanical) or do all stimuli converge to a single signaling pathway upstream of the autophagy machinery? Can modulation of autophagy contribute to the restoration of cilium functions?Receptors, transporters and specialized plasma membrane structures such as cilia constitute the interfaces between the extracellular and intracellular milieu and allow the cells to trigger specific responses to adapt to changes imposed by the environment. Among these adaptive responses, macroautophagy (hereafter referred to as 'autophagy') is a catabolic process conserved in eukaryotic cells by which the cell recycles its own constituents. 1 Autophagy is involved in the adaptation to starvation, cell differentiation and development, the degradation of aberrant structure...

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“…However, modification of the MTs had a greater effect, with low-dose taxol treatment allowing integrins into the initial segment and proximal axon. Taxol has many effects on MTs, including on acetylation, tyrosination, and polyglutamylation (Hammond et al, 2010;Nakata et al, 2011;Kee et al, 2012). Increasing acetylation with a deacetylase inhibitor did not have the same effect.…”

Section: Why Do Integrins Become Excluded From Axons?mentioning

confidence: 99%

Exclusion of Integrins from CNS Axons Is Regulated by Arf6 Activation and the AIS

et al. 2015

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Integrins are adhesion and survival molecules involved in axon growth during CNS development, as well as axon regeneration after injury in the peripheral nervous system (PNS). Adult CNS axons do not regenerate after injury, partly due to a low intrinsic growth capacity. We have previously studied the role of integrins in axon growth in PNS axons; in the present study, we investigate whether integrin mechanisms involved in PNS regeneration may be altered or lacking from mature CNS axons by studying maturing CNS neurons in vitro. In rat cortical neurons, we find that integrins are present in axons during initial growth but later become restricted to the somato-dendritic domain. We investigated how this occurs and whether it can be altered to enhance axonal growth potential. We find a developmental change in integrin trafficking; transport becomes predominantly retrograde throughout axons, but not dendrites, as neurons mature. The directionality of transport is controlled through the activation state of ARF6, with developmental upregulation of the ARF6 GEF ARNO enhancing retrograde transport. Lowering ARF6 activity in mature neurons restores anterograde integrin flow, allows transport into axons, and increases axon growth. In addition, we found that the axon initial segment is partly responsible for exclusion of integrins and removal of this structure allows integrins into axons. Changing posttranslational modifications of tubulin with taxol also allows integrins into the proximal axon. The experiments suggest that the developmental loss of regenerative ability in CNS axons is due to exclusion of growth-related molecules due to changes in trafficking.

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A size-exclusion permeability barrier and nucleoporins characterize a ciliary pore complex that regulates transport into cilia

Cited by 292 publications

References 39 publications

Avalanche-like behavior in ciliary import

Avalanche-like behavior in ciliary import

Autophagy and regulation of cilia function and assembly

Exclusion of Integrins from CNS Axons Is Regulated by Arf6 Activation and the AIS

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