Birefringence Imaging Directly Reveals Architectural Dynamics of Filamentous Actin in Living Growth Cones

Katoh, K.; Hammar, Katherine; Smith, Peter J. S.; Oldenbourg, Rudolf

doi:10.1091/mbc.10.1.197

Cited by 114 publications

(120 citation statements)

References 51 publications

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“…Actin filaments in both regions undergo continuous retrograde flow (Forscher and Smith, 1988;Welnhofer et al, 1997;Mallavarapu and Mitchison, 1999). Previous studies have shown that filamentous actin in the transition region of the growth cone can take more sinuous forms termed "intrapodia" that polymerize outward and protrude into the lamellipodium (Katoh et al, 1999;Rochlin et al, 1999). As shown in one example of a large paused growth cone in Figure 6 A, actin filaments, resembling intrapodia, polymerize from the transition region outward into the periphery of the lamellipodium and depolymerize back toward the transition region (Fig.…”

Section: F-actin-microtubule Interactions Involve Copolymerizationmentioning

confidence: 82%

Axon Branching Requires Interactions between Dynamic Microtubules and Actin Filaments

Dent¹,

2001

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Cortical neurons innervate many of their targets by collateral axon branching, which requires local reorganization of the cytoskeleton. We coinjected cortical neurons with fluorescently labeled tubulin and phalloidin and used fluorescence timelapse imaging to analyze interactions between microtubules and actin filaments (F-actin) in cortical growth cones and axons undergoing branching. In growth cones and at axon branch points, splaying of looped or bundled microtubules is accompanied by focal accumulation of F-actin. Dynamic microtubules colocalize with F-actin in transition regions of growth cones and at axon branch points. In contrast, F-actin is excluded from the central region of the growth cone and the axon shaft, which contains stable microtubules. Interactions between dynamic microtubules and dynamic actin filaments involve their coordinated polymerization and depolymerization. Application of drugs that attenuate either microtubule or F-actin dynamics also inhibits polymerization of the other cytoskeletal element. Importantly, inhibition of microtubule or F-actin dynamics prevents axon branching but not axon elongation. However, these treatments do cause undirected axon outgrowth. These results suggest that interactions between dynamic microtubules and actin filaments are required for axon branching and directed axon outgrowth. Key words: microtubule; actin filament; growth cone; collateral axon branching; cortical development; fluorescence timelapse imagingAxons are guided in new directions by reorientation of their growth cones as well as extension of collateral branches (O'Leary et al., 1990). We have shown previously (Szebenyi et al., 1998) that cortical axon branching occurs in vitro through changes in growth cone morphologies and behaviors. Growth cones at the tips of rapidly extending cortical axons are typically small and highly motile. However, in preparation for branching, growth cones pause for many hours, greatly enlarge, and maintain motility without forward advance. Subsequently, a new growth cone develops from the tip of the large paused growth cone and forms the new leading axon. Remnants of the large paused growth cone remain behind on the axon shaft as filopodial and lamellar expansions that subsequently give rise to interstitial axon collaterals. In living cortical slices (Halloran and Kalil, 1994), similar growth cone pausing behaviors were observed in the corpus callosum in regions where collateral axon branches develop and extend toward cortical targets, suggesting that growth cone pausing is closely related to branching mechanisms in vivo.Changes in the direction of axon outgrowth depend on reorganization of the microtubule and actin cytoskeleton (Lin and

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Section: F-actin-microtubule Interactions Involve Copolymerizationmentioning

confidence: 82%

Axon Branching Requires Interactions between Dynamic Microtubules and Actin Filaments

Dent¹,

2001

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“…It is possible that assembly occurs by polymerization of F-actin on the end of the cable within the assembly site. Localized polymerization of F-actin occurs in a variety of cells, including at the leading edge of motile cells and filopodia of neurons (22,23). If actin cable elongation is driven by actin polymerization in yeast, then the fast-growing (barbed) end of actin filaments within cables is probably directed toward the bud.…”

Section: Discussionmentioning

confidence: 99%

Actin cable dynamics in budding yeast

Yang

Pon

2002

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

187

200

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Actin cables, bundles of actin filaments that align along the long axis of budding yeast, are crucial for establishment of cell polarity. We fused green fluorescent protein (GFP) to actin binding protein 140 (Abp140p) and visualized actin cable dynamics in living yeast. We detected two populations of actin cables: (i) bud-associated cables, which extend from the bud along the mother-bud axis, and (ii) randomly oriented cables, which are relatively short. Time-lapse imaging of Abp140p-GFP revealed an apparent increase in the length of bud-associated actin cables. Analysis of movement of Abp140p-GFP fiduciary marks on bud-associated cables and fluorescence loss in photobleaching experiments revealed that this apparent elongation occurs by assembly of new material at the end of the cable within the bud and movement of the opposite end of the cable toward the tip of the mother cell distal to the bud. The rate of extension of the tip of an elongating actin cable is 0.29 ؎ 0.08 m͞s. Latrunculin A (Lat-A) treatment completely blocked this process. We also observed movement of randomly oriented cables around the cortex of cells at a rate of 0.59 ؎ 0.14 m͞s. Mild treatment with Lat-A did not affect the velocity of movement of randomly oriented cables. However, Lat-A treatment did increase the number of randomly oriented, motile cables per cell. Our observations suggest that establishment of bud-associated actin cables during the cell cycle is accomplished not by realignment of existing cables but by assembly of new cables within the bud or bud neck, followed by elongation.

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“…Anisotropic suspensions (12,13) and phases of bent-core molecules (14) have attracted a great deal of attention because of their unique properties and potential applications. Anisotropic self-organization in a living cell's interior may play a vital biological function and is readily observed by means of birefringence imaging (15,16). Recently, there has been a growing interest in optical trapping in anisotropic media (17)(18)(19)(20)(21)(22).…”

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confidence: 99%

Laser trapping in anisotropic fluids and polarization-controlled particle dynamics

Smalyukh

Kachynski

Kuzmin

et al. 2006

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

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Anisotropic fluids are widespread, ranging from liquid crystals used in displays to ordered states of a biological cell interior. Optical trapping is potentially a powerful technique in the fundamental studies and applications of anisotropic fluids. We demonstrate that laser beams in these fluids can generate anisotropic optical trapping forces, even for particles larger than the trapping beam wavelength. Immersed colloidal particles modify the fluid's ordered molecular structures and locally distort its optic axis. This distortion produces a refractive index ''corona'' around the particles that depends on their surface characteristics. The laser beam can trap such particles not only at their center but also at the high-index corona. Trapping forces in the beam's lateral plane mimic the corona and are polarizationcontrolled. This control allows the optical forces to be reversed and cause the particle to follow a prescribed trajectory. Anisotropic particle dynamics in the trap varies with laser power because of the anisotropy of both viscous drag and trapping forces. Using thermotropic liquid crystals and biological materials, we show that these phenomena are quite general for all anisotropic fluids and impinge broadly on their quantitative studies using laser tweezers. Potential applications include modeling thermodynamic systems with anisotropic polarization-controlled potential wells, producing optically tunable photonic crystals, and fabricating light-controlled nano-and micropumps.colloids ͉ laser tweezers ͉ liquid crystals ͉ optical trapping ͉ defects

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Birefringence Imaging Directly Reveals Architectural Dynamics of Filamentous Actin in Living Growth Cones

Cited by 114 publications

References 51 publications

Axon Branching Requires Interactions between Dynamic Microtubules and Actin Filaments

Axon Branching Requires Interactions between Dynamic Microtubules and Actin Filaments

Actin cable dynamics in budding yeast

Laser trapping in anisotropic fluids and polarization-controlled particle dynamics

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