scholarly journals Dynamics of the IFT machinery at the ciliary tip

eLife ◽  
2017 ◽  
Vol 6 ◽  
Author(s):  
Alexander Chien ◽  
Sheng Min Shih ◽  
Raqual Bower ◽  
Douglas Tritschler ◽  
Mary E Porter ◽  
...  
Keyword(s):  
Basal Body ◽  
Full Range ◽  
Intraflagellar Transport ◽  
Feedback Mechanism ◽  
Conventional Imaging ◽  
Range Of Movement ◽  
Anterograde Transport ◽  
Traffic Jam ◽  
Negative Feedback Mechanism ◽  
Cilia And Flagella

Intraflagellar transport (IFT) is essential for the elongation and maintenance of eukaryotic cilia and flagella. Due to the traffic jam of multiple trains at the ciliary tip, how IFT trains are remodeled in these turnaround zones cannot be determined by conventional imaging. Using PhotoGate, we visualized the full range of movement of single IFT trains and motors in Chlamydomonas flagella. Anterograde trains split apart and IFT complexes mix with each other at the tip to assemble retrograde trains. Dynein-1b is carried to the tip by kinesin-II as inactive cargo on anterograde trains. Unlike dynein-1b, kinesin-II detaches from IFT trains at the tip and diffuses in flagella. As the flagellum grows longer, diffusion delays return of kinesin-II to the basal body, depleting kinesin-II available for anterograde transport. Our results suggest that dissociation of kinesin-II from IFT trains serves as a negative feedback mechanism that facilitates flagellar length control in Chlamydomonas.

scholarly journals Dynamics of the IFT Machinery at the Ciliary Tip

2017 ◽  
Author(s):  
Alexander Chien ◽  
Sheng Min Shih ◽  
Raqual Bower ◽  
Douglas Tritschler ◽  
Mary E. Porter ◽  
...  
Keyword(s):  
Basal Body ◽  
Full Range ◽  
Intraflagellar Transport ◽  
Feedback Mechanism ◽  
Conventional Imaging ◽  
Range Of Movement ◽  
Anterograde Transport ◽  
Traffic Jam ◽  
Negative Feedback Mechanism ◽  
Cilia And Flagella

AbstractIntraflagellar transport (IFT) is essential for the elongation and maintenance of eukaryotic cilia and flagella. Due to the traffic jam of multiple trains at the ciliary tip, how IFT trains are remodeled in these turnaround zones cannot be determined by conventional imaging. Using Photogate, we visualized the full range of movement of single IFT trains and motors inChlamydomonasflagella. Anterograde trains split apart and IFT complexes mix with each other at the tip to assemble retrograde trains. Dynein-1b is carried to the tip by kinesin-II as inactive cargo on anterograde trains. Unlike dynein-1b, kinesin-II detaches from IFT trains at the tip and diffuses in flagella. As the flagellum grows longer, diffusion delays return of kinesin-II to the basal body, depleting kinesin-II available for anterograde transport. Our results suggest that dissociation of kinesin-II from IFT trains serves as a negative feedback mechanism that facilitates flagellar length control inChlamydomonas.

scholarly journals The intraflagellar transport dynein complex of trypanosomes is made of a heterodimer of dynein heavy chains and of light and intermediate chains of distinct functions

2014 ◽  
Vol 25 (17) ◽  
pp. 2620-2633 ◽  
Author(s):  
Thierry Blisnick ◽  
Johanna Buisson ◽  
Sabrina Absalon ◽  
Alexandra Marie ◽  
Nadège Cayet ◽  
...  
Keyword(s):  
Protein Complexes ◽  
Intraflagellar Transport ◽  
Retrograde Transport ◽  
High Concentration ◽  
Anterograde Transport ◽  
Heavy Chains ◽  
Cilia And Flagella ◽  
The Stability ◽  
Intermediate Chains ◽  
Dynein Heavy Chains

Cilia and flagella are assembled by intraflagellar transport (IFT) of protein complexes that bring tubulin and other precursors to the incorporation site at their distal tip. Anterograde transport is driven by kinesin, whereas retrograde transport is ensured by a specific dynein. In the protist Trypanosoma brucei, two distinct genes encode fairly different dynein heavy chains (DHCs; ∼40% identity) termed DHC2.1 and DHC2.2, which form a heterodimer and are both essential for retrograde IFT. The stability of each heavy chain relies on the presence of a dynein light intermediate chain (DLI1; also known as XBX-1/D1bLIC). The presence of both heavy chains and of DLI1 at the base of the flagellum depends on the intermediate dynein chain DIC5 (FAP133/WDR34). In the IFT140RNAi mutant, an IFT-A protein essential for retrograde transport, the IFT dynein components are found at high concentration at the flagellar base but fail to penetrate the flagellar compartment. We propose a model by which the IFT dynein particle is assembled in the cytoplasm, reaches the base of the flagellum, and associates with the IFT machinery in a manner dependent on the IFT-A complex.

scholarly journals Different Effects of Tetrahymena IFT172 Domains on Anterograde and Retrograde Intraflagellar Transport

2008 ◽  
Vol 19 (4) ◽  
pp. 1450-1461 ◽  
Author(s):  
Che-Chia Tsao ◽  
Martin A. Gorovsky
Keyword(s):  
Basal Body ◽  
Intraflagellar Transport ◽  
Retrograde Transport ◽  
Terminal Repeat ◽  
Anterograde Transport ◽  
Multiprotein Complexes ◽  
Repeat Domain

Intraflagellar transport (IFT) particles are multiprotein complexes that move bidirectionally along the cilium/flagellum. The Tetrahymena IFT172 gene encodes a protein with an N-terminal WD domain (WDD) and a C-terminal repeat domain (RPD). Epitope-tagged Ift172p localized to the basal body and in cilia along the axoneme, and IFT172 knockout cells lost cilia and motility. Using serial deletion constructs to rescue the knockout cells, we found that neither the WDD nor the RPD alone is sufficient to assemble cilia. Ift172p containing only the WDD or the RPD failed to enter cilia. Constructs with a partial truncation of the RPD still rescued although cilia were assembled less efficiently, indicating that the WDD and a part of the RPD are sufficient for anterograde transport. Partial truncation of the RPD caused the accumulation of truncated Ift172p itself and of Ift88p at ciliary tips, suggesting that IFT turnaround or retrograde transport was affected. These results implicate different regions of Ift172p in different steps of the IFT process.

scholarly journals The GTPase IFT27 is involved in both anterograde and retrograde intraflagellar transport

eLife ◽  
2014 ◽  
Vol 3 ◽  
Author(s):  
Diego Huet ◽  
Thierry Blisnick ◽  
Sylvie Perrot ◽  
Philippe Bastin
Keyword(s):  
Trypanosoma Brucei ◽  
Protein Complexes ◽  
Intraflagellar Transport ◽  
Retrograde Transport ◽  
Small Gtpase ◽  
Anterograde Transport ◽  
Cargo Transport ◽  
Cilia And Flagella ◽  
Bidirectional Movement

The construction of cilia and flagella depends on intraflagellar transport (IFT), the bidirectional movement of two protein complexes (IFT-A and IFT-B) driven by specific kinesin and dynein motors. IFT-B and kinesin are associated to anterograde transport whereas IFT-A and dynein participate to retrograde transport. Surprisingly, the small GTPase IFT27, a member of the IFT-B complex, turns out to be essential for retrograde cargo transport in Trypanosoma brucei. We reveal that this is due to failure to import both the IFT-A complex and the IFT dynein into the flagellar compartment. To get further molecular insight about the role of IFT27, GDP- or GTP-locked versions were expressed in presence or absence of endogenous IFT27. The GDP-locked version is unable to enter the flagellum and to interact with other IFT-B proteins and its sole expression prevents flagellum formation. These findings demonstrate that a GTPase-competent IFT27 is required for association to the IFT complex and that IFT27 plays a role in the cargo loading of the retrograde transport machinery.

scholarly journals Intraflagellar Transport and Functional Analysis of Genes Required for Flagellum Formation in Trypanosomes

2008 ◽  
Vol 19 (3) ◽  
pp. 929-944 ◽  
Author(s):  
Sabrina Absalon ◽  
Thierry Blisnick ◽  
Linda Kohl ◽  
Géraldine Toutirais ◽  
Gwénola Doré ◽  
...  
Keyword(s):  
Trypanosoma Brucei ◽  
Fluorescent Protein ◽  
Protein Complexes ◽  
Intraflagellar Transport ◽  
Retrograde Transport ◽  
Anterograde Transport ◽  
Body Regions ◽  
Cilia And Flagella ◽  
Bidirectional Movement ◽  
Green Fluorescent

Intraflagellar transport (IFT) is the bidirectional movement of protein complexes required for cilia and flagella formation. We investigated IFT by analyzing nine conventional IFT genes and five novel putative IFT genes (PIFT) in Trypanosoma brucei that maintain its existing flagellum while assembling a new flagellum. Immunostaining against IFT172 or expression of tagged IFT20 or green fluorescent protein GFP::IFT52 revealed the presence of IFT proteins along the axoneme and at the basal body and probasal body regions of both old and new flagella. IFT particles were detected by electron microscopy and exhibited a strict localization to axonemal microtubules 3–4 and 7–8, suggesting the existence of specific IFT tracks. Rapid (>3 μm/s) bidirectional intraflagellar movement of GFP::IFT52 was observed in old and new flagella. RNA interference silencing demonstrated that all individual IFT and PIFT genes are essential for new flagellum construction but the old flagellum remained present. Inhibition of IFTB proteins completely blocked axoneme construction. Absence of IFTA proteins (IFT122 and IFT140) led to formation of short flagella filled with IFT172, indicative of defects in retrograde transport. Two PIFT proteins turned out to be required for retrograde transport and three for anterograde transport. Finally, flagellum membrane elongation continues despite the absence of axonemal microtubules in all IFT/PIFT mutant.

scholarly journals The FLA3 KAP Subunit Is Required for Localization of Kinesin-2 to the Site of Flagellar Assembly and Processive Anterograde Intraflagellar Transport

2005 ◽  
Vol 16 (3) ◽  
pp. 1341-1354 ◽  
Author(s):  
Joshua Mueller ◽  
Catherine A. Perrone ◽  
Raqual Bower ◽  
Douglas G. Cole ◽  
Mary E. Porter
Keyword(s):  
Amino Acid ◽  
Basal Body ◽  
Intraflagellar Transport ◽  
Body Region ◽  
Wild Type ◽  
Gene Encoding ◽  
Flagellar Assembly ◽  
Cilia And Flagella ◽  
Preferential Incorporation ◽  
Dic Microscopy

Intraflagellar transport (IFT) is a bidirectional process required for assembly and maintenance of cilia and flagella. Kinesin-2 is the anterograde IFT motor, and Dhc1b/Dhc2 drives retrograde IFT. To understand how either motor interacts with the IFT particle or how their activities might be coordinated, we characterized a ts mutation in the Chlamydomonas gene encoding KAP, the nonmotor subunit of Kinesin-2. The fla3-1 mutation is an amino acid substitution in a conserved C-terminal domain. fla3-1 strains assemble flagella at 21°C, but cannot maintain them at 33°C. Although the Kinesin-2 complex is present at both 21 and 33°C, the fla3-1 Kinesin-2 complex is not efficiently targeted to or retained in the basal body region or flagella. Video-enhanced DIC microscopy of fla3-1 cells shows that the frequency of anterograde IFT particles is significantly reduced. Anterograde particles move at near wild-type velocities, but appear larger and pause more frequently in fla3-1. Transformation with an epitope-tagged KAP gene rescues all of the fla3-1 defects and results in preferential incorporation of tagged KAP complexes into flagella. KAP is therefore required for the localization of Kinesin-2 at the site of flagellar assembly and the efficient transport of anterograde IFT particles within flagella.

scholarly journals Electron-tomographic analysis of intraflagellar transport particle trains in situ

2009 ◽  
Vol 187 (1) ◽  
pp. 135-148 ◽  
Author(s):  
Gaia Pigino ◽  
Stefan Geimer ◽  
Salvatore Lanzavecchia ◽  
Eugenio Paccagnini ◽  
Francesca Cantele ◽  
...  
Keyword(s):  
Intraflagellar Transport ◽  
Sensory Function ◽  
Anterograde Transport ◽  
Transmission Electron ◽  
Transport Particle ◽  
Cilia And Flagella ◽  
Bidirectional Movement ◽  
The Individual ◽  
Tomographic Analysis

Intraflagellar transport (IFT) is the bidirectional movement of multipolypeptide particles between the ciliary membrane and the axonemal microtubules, and is required for the assembly, maintenance, and sensory function of cilia and flagella. In this paper, we present the first high-resolution ultrastructural analysis of trains of flagellar IFT particles, using transmission electron microscopy and electron-tomographic analysis of sections from flat-embedded Chlamydomonas reinhardtii cells. Using wild-type and mutant cells with defects in IFT, we identified two different types of IFT trains: long, narrow trains responsible for anterograde transport; and short, compact trains underlying retrograde IFT. Both types of trains have characteristic repeats and patterns that vary as one sections longitudinally through the trains of particles. The individual IFT particles are highly complex, bridged to each other and to the outer doublet microtubules, and are closely apposed to the inner surface of the flagellar membrane.

Ultrastructural morphology of nontumorous lactotrophs in human pituitaries exposed to high prolactin levels

1987 ◽  
Vol 45 ◽  
pp. 896-897
Author(s):  
S. Jalalah ◽  
K. Kovacs ◽  
E. Horvath
Keyword(s):  
Anterior Pituitary ◽  
Secretory Activity ◽  
Pituitary Hormones ◽  
Feedback Mechanism ◽  
Endocrine Activity ◽  
Hormone Synthesis ◽  
Anterior Pituitary Hormones ◽  
Negative Feedback Mechanism ◽  
Ultrastructural Morphology ◽  
Transmission Electron

Lactotrophs, as many other endocrine cells, change their morphology in response to factors influencing their secretory activity. Secretion of prolactin (PRL) from lactotrophs, like that of other anterior pituitary hormones, is under the control of the hypothalamus. Unlike most anterior pituitary hormones, PRL has no apparent target gland which could modulate the endocrine activity of lactotrophs. It is generally agreed that PRL regulates its own release from lactotrophs via the short loop negative feedback mechanism exerted at the level of the hypothalamus or the pituitary. Accordingly, ultrastructural morphology of lactotrophs is not constant; it is changing in response to high PRL levels showing signs of suppressed hormone synthesis and secretion.By transmission electron microscopy and morphometry, we have studied the morphology of lactotrophs in nontumorous (NT) portions of 7 human pituitaries containing PRL-secreting adenoma; these lactotrophs were exposed to abnormally high PRL levels.

scholarly journals Regulation of Store-Operated Ca2+ Entry by SARAF

Cells ◽  
2021 ◽  
Vol 10 (8) ◽  
pp. 1887
Author(s):  
Inbal Dagan ◽  
Raz Palty
Keyword(s):  
Molecular Mechanisms ◽  
Feedback Mechanism ◽  
Cellular Biology ◽  
Excitable Cells ◽  
Major Pathway ◽  
Negative Feedback Mechanism ◽  
Crac Channels ◽  
Dependent Inactivation ◽  
Crac Channel ◽  
The One

Calcium (Ca2+) signaling plays a dichotomous role in cellular biology, controlling cell survival and proliferation on the one hand and cellular toxicity and cell death on the other. Store-operated Ca2+ entry (SOCE) by CRAC channels represents a major pathway for Ca2+ entry in non-excitable cells. The CRAC channel has two key components, the endoplasmic reticulum Ca2+ sensor stromal interaction molecule (STIM) and the plasma-membrane Ca2+ channel Orai. Physical coupling between STIM and Orai opens the CRAC channel and the resulting Ca2+ flux is regulated by a negative feedback mechanism of slow Ca2+ dependent inactivation (SCDI). The identification of the SOCE-associated regulatory factor (SARAF) and investigations of its role in SCDI have led to new functional and molecular insights into how SOCE is controlled. In this review, we provide an overview of the functional and molecular mechanisms underlying SCDI and discuss how the interaction between SARAF, STIM1, and Orai1 shapes Ca2+ signaling in cells.

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