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Intraflagellar transport: the eyes have it.

Rosenbaum JL, Cole DG, Diener DR - J. Cell Biol. (1999)

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular, Cellular, and Developmental Biology, Yale University, New Haven, Connecticut 06520-8103, USA. joel.rosenbaum@yale.edu

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This elongated organelle must import all the macromolecules required for its assembly, maintenance, and function including >200 polypeptides that make up the microtubular axoneme, all the constituents of the flagellar membrane, as well as a prodigious amount of ATP to supply the thousands of dynein motors that drive flagellar motility... When cells with full-length flagella lacking radial spokes were fused to wild-type cells, radial spokes from the wild-type cytoplasm entered the spokeless flagella, assembled at the distal tips of the flagella, and gradually continued assembly toward the base... Similar results were obtained with inner dynein arms... Many flagellar proteins exist as complexes of multiple polypeptides, e.g., the radial spokes contain 17 polypeptides and the outer dynein arms contain >15 polypeptides ; it would be advantageous for the cell to preassemble these axonemal structures in the cytoplasm rather than to send individual polypeptides into the flagella for assembly... In keeping with this idea, assembled radial spoke complexes have been found in the cytoplasm of Chlamydomonas (Diener, D.R., D.G... The movement is continuous and linear along the entire flagella... IFT is neither affected by mutations that cause immotile flagella, e.g., mutations affecting dynein arms, radial spokes, or central pair microtubules, nor does it appear to be related to other motilities associated with the flagellar membrane, e.g., gliding of whole cells on surfaces by means of their outstretched flagella or the movement of polystyrene beads on the flagellar surface... As is typical for kinesins and their cargoes, FLA10 kinesin-II does not copurify with IFT particles; however, a small amount of FLA10 coprecipitates with immunoprecipitates of IFT particle polypeptides, suggesting a weak interaction between FLA10 kinesin-II and IFT particles... The IFT particles were purified from flagellar extracts taking advantage of the fact that they are greatly decreased in flagella of fla10 cells maintained at the restrictive temperature. 15 polypeptides sedimenting at ∼16 S are reduced in flagella of fla10 cells incubated at 32°C... In these C. elegans mutants, the ability to sense osmotic gradients and chemoattractants is lacking... The basis for the mutant phenotype at the cellular level is that the sensory cilia found at dendritic ends of sensory neurons do not assemble properly... Thus, IFT particle proteins and the motors that move them, kinesin-II and cytoplasmic dynein DHC1b, are essential for the assembly of neuronal nonmotile sensory cilia of C. elegans... The molecular motors, FLA10 kinesin-II and cytoplasmic dynein DHC1b, responsible for transporting these precursors into and out of the flagella and the IFT particle polypeptides are concentrated around the basal bodies and may become associated with each other as well as with the flagellar precursors in this region... Although the above discussion has emphasized the importance of IFT in transporting flagellar axonemal precursors into the flagella, it is important to note that (a) the IFT rafts are clearly associated with the flagellar membrane as well as the B tubule of the outer doublets; (b) axonemal components, e.g., radial spokes, dynein arms, and central pair microtubules, are absent from immotile sensory cilia of C. elegans and vertebrate photoreceptors; and (c) the first phenotype that appears (in ∼30 min) in fla10 cells at the restrictive temperature is a membrane defect: the cells lose the ability to mate by use of their flagella.

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Transmission electron micrographs of a Chlamydomonas flagellum (micrograph courtesy of Karl A. Johnson) and a  vertebrate rod connecting cilium (reprinted with permission from  Sandborn, 1970). Note the presence of a raft (arrows) in both organelles.
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Figure 1: Transmission electron micrographs of a Chlamydomonas flagellum (micrograph courtesy of Karl A. Johnson) and a vertebrate rod connecting cilium (reprinted with permission from Sandborn, 1970). Note the presence of a raft (arrows) in both organelles.

Mentions: Thin sectioning and electron microscopy indicate that the material moving beneath the flagellar membrane by IFT consists of “lollipop-shaped” particles occurring in groups of varying particle numbers, called “rafts” (Fig. 1; Kozminski et al., 1993). The rafts, initially observed by Ringo (1967) during ultrastructural analysis of the Chlamydomonas flagellum, are attached by a thin connection to the B-subfibers of the outer-doublet microtubules and to the overlying flagellar membrane (Kozminski et al., 1993). Electron microscopy of IFT particles observed by DIC in the flagellum of a single embedded cell confirmed that the particles observed by DIC are, indeed, the rafts observed by electron microscopy (Kozminski et al., 1995).


Intraflagellar transport: the eyes have it.

Rosenbaum JL, Cole DG, Diener DR - J. Cell Biol. (1999)

Transmission electron micrographs of a Chlamydomonas flagellum (micrograph courtesy of Karl A. Johnson) and a  vertebrate rod connecting cilium (reprinted with permission from  Sandborn, 1970). Note the presence of a raft (arrows) in both organelles.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2132910&req=5

Figure 1: Transmission electron micrographs of a Chlamydomonas flagellum (micrograph courtesy of Karl A. Johnson) and a vertebrate rod connecting cilium (reprinted with permission from Sandborn, 1970). Note the presence of a raft (arrows) in both organelles.
Mentions: Thin sectioning and electron microscopy indicate that the material moving beneath the flagellar membrane by IFT consists of “lollipop-shaped” particles occurring in groups of varying particle numbers, called “rafts” (Fig. 1; Kozminski et al., 1993). The rafts, initially observed by Ringo (1967) during ultrastructural analysis of the Chlamydomonas flagellum, are attached by a thin connection to the B-subfibers of the outer-doublet microtubules and to the overlying flagellar membrane (Kozminski et al., 1993). Electron microscopy of IFT particles observed by DIC in the flagellum of a single embedded cell confirmed that the particles observed by DIC are, indeed, the rafts observed by electron microscopy (Kozminski et al., 1995).

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular, Cellular, and Developmental Biology, Yale University, New Haven, Connecticut 06520-8103, USA. joel.rosenbaum@yale.edu

AUTOMATICALLY GENERATED EXCERPT
Please rate it.

This elongated organelle must import all the macromolecules required for its assembly, maintenance, and function including >200 polypeptides that make up the microtubular axoneme, all the constituents of the flagellar membrane, as well as a prodigious amount of ATP to supply the thousands of dynein motors that drive flagellar motility... When cells with full-length flagella lacking radial spokes were fused to wild-type cells, radial spokes from the wild-type cytoplasm entered the spokeless flagella, assembled at the distal tips of the flagella, and gradually continued assembly toward the base... Similar results were obtained with inner dynein arms... Many flagellar proteins exist as complexes of multiple polypeptides, e.g., the radial spokes contain 17 polypeptides and the outer dynein arms contain >15 polypeptides ; it would be advantageous for the cell to preassemble these axonemal structures in the cytoplasm rather than to send individual polypeptides into the flagella for assembly... In keeping with this idea, assembled radial spoke complexes have been found in the cytoplasm of Chlamydomonas (Diener, D.R., D.G... The movement is continuous and linear along the entire flagella... IFT is neither affected by mutations that cause immotile flagella, e.g., mutations affecting dynein arms, radial spokes, or central pair microtubules, nor does it appear to be related to other motilities associated with the flagellar membrane, e.g., gliding of whole cells on surfaces by means of their outstretched flagella or the movement of polystyrene beads on the flagellar surface... As is typical for kinesins and their cargoes, FLA10 kinesin-II does not copurify with IFT particles; however, a small amount of FLA10 coprecipitates with immunoprecipitates of IFT particle polypeptides, suggesting a weak interaction between FLA10 kinesin-II and IFT particles... The IFT particles were purified from flagellar extracts taking advantage of the fact that they are greatly decreased in flagella of fla10 cells maintained at the restrictive temperature. 15 polypeptides sedimenting at ∼16 S are reduced in flagella of fla10 cells incubated at 32°C... In these C. elegans mutants, the ability to sense osmotic gradients and chemoattractants is lacking... The basis for the mutant phenotype at the cellular level is that the sensory cilia found at dendritic ends of sensory neurons do not assemble properly... Thus, IFT particle proteins and the motors that move them, kinesin-II and cytoplasmic dynein DHC1b, are essential for the assembly of neuronal nonmotile sensory cilia of C. elegans... The molecular motors, FLA10 kinesin-II and cytoplasmic dynein DHC1b, responsible for transporting these precursors into and out of the flagella and the IFT particle polypeptides are concentrated around the basal bodies and may become associated with each other as well as with the flagellar precursors in this region... Although the above discussion has emphasized the importance of IFT in transporting flagellar axonemal precursors into the flagella, it is important to note that (a) the IFT rafts are clearly associated with the flagellar membrane as well as the B tubule of the outer doublets; (b) axonemal components, e.g., radial spokes, dynein arms, and central pair microtubules, are absent from immotile sensory cilia of C. elegans and vertebrate photoreceptors; and (c) the first phenotype that appears (in ∼30 min) in fla10 cells at the restrictive temperature is a membrane defect: the cells lose the ability to mate by use of their flagella.

Show MeSH
Related in: MedlinePlus