Yoshio Fukui: Chap. 4.

Cytoskeleton

Cytoskeleton is organized in a spatially and temporally specific manner.

Like muscle, cell moves by consuming adnosine-triphosphate (ATP) and the chemical energy is transduced into mechanical forces. The cellular components responsible for cell movement are called "cytoskeleton". The cytoskeleton consists of actin filaments, microtubules, intermediate filaments and their associated proteins such as actin-binding proteins (ABP's), microtubule-associated proteins (MAP's), and hundreds other proteins. The major ABP's include myosin-I and II, picture below. Those proteins are organized and localized in temporally and spatially regulated manner (ref. 2, 13-16). Example of the localization is shown below.

Actin (red), Myosin II (green)

(Credit) Late Philip Presley, MBL: Fluorescence filter tuning of Zeiss Photomicroscope- III, allowing precise registration for the dual channel exposures.

Myosin I (green), Myosin II (red)

(Credit) Dr. Edward Korn, Dr. Thomas Lynch, NIH: Polyclonal anti-Acanthamoeba myosin-I antibody, which for the first time revealed a unique localization to myosin isoforms (ref. 15).

Actin (red), Microtubules (green)

(Credit) Dr. Steven Blose, Cold Spring Harbor Laboratory: Monoclonal anti-chicken brain alpha-tubulin antibody, demonstrating striking microtubule organization during cell division (ref. 13, 14).

 

Localization of a representative actin-binding protein, alpha-actinin, to the cortical and lamellipodial F-actin networks. Note that, in dividing cells, alpha-actin is not associated to F-actin in the contractile ring in a measurable manner. The mechanism underlying specific binding of actin-binding proteins to certain F-actin population is unknown. (Monoclonal anti-alpha-actinin antibody: Courtesy of Dr. Michael Schleicher, Germany).

(Note) Images shown here were acquired by epi-fluorescence microscopy in cells prepared by "agar-overlay" technique. In this technique, cells are made more or less two-dimensional with the average thickness of 3 micrometers. Under this condition, much of optical noise coming from different focal planes can be eliminated providing superior image quality (ref 1-4). For those who are interested in this technique, the pdf file is here:

pdf file: Yoshio Fukui "Agaroverlay Technique"

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Representative studies on the cytoskeletal organization using the agaroverly technique:

Fukui, Y., Lynch, T. J., Brzeska, H., and Korn, E. D. (1989). Myosin I is located at the leading edges of locomoting Dictyostelium amoebae. Nature 341, 328-331.

In this study, we demonstrated that two myosin isoforms, myosin I and myosin II, are localized in a unique fashion. The muscle type, myosin II, is located in the cleavarge furrow (orange) in dividing cell and in the rear of migrating cell. In contrast, myosin I, a novel single-headed monomeric myosin (green), is located in the polar lamellas in dividing cell and in leading edges of migrating cell.

This study was made possible in collaboration with Dr. Edward Korn of the National Institutes of Health.

Myosin I and II localization in migrating cell: see "Molecular Biology of the Cell", v. 4 (2002), Fig. 16-93.

 

Fukui, Y., A. De Lozanne, and J. A. Spudich (1990). Structure and function of the cytoskeleton of a Dictyostelium myosin-defective mutant. J. Cell Biol. 110, 367-378.

In this study, we demonstrated that a mutant in which the normal myosin II was replaced with a truncated form, heavy meromyosin (hmm), is defective in cytokenesis and mobility of surface receptors (Con-A capping), and myosin II is localized only diffusely in the cytoplasm (left). Interestingly we found that actin filaments (right) are organized in apparently similar manner as the wild type cell. This finding helped establishing a then new idea that actin cytoskeleton is the key framework, which is associated with various binding proteins including myosin II in spatially unique manners.

This study was made possible in collaboration with Dr. James Spudich of Stanford University.

Distinct distribution of actin and myosin II at the contractile ring: see "Molecular Biology of the Cell", v. 4 (2002), Fig. 18-34.

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For more about my work, please click links below:

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Images and movies used in this site consist of my original work and protected by the 1976 Copyright Act (Title 17, US Code).

1. US Copyright Registration Certificate No. VAu 572-317: Yoshio Fukui "Digital Petroglyphs of the Cell 2002".

2. US Copyright Registration Certificate No. VAu 585-357: Yoshio Fukui "Mycrodynamics of the Cell".

(Last modified: 12/10/2004)

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