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Actin filament dynamics are dominated by rapid growth and severing activity in the Arabidopsis cortical array.

Staiger CJ, Sheahan MB, Khurana P, Wang X, McCurdy DW, Blanchoin L - J. Cell Biol. (2009)

Bottom Line: Remodeling of the cortical actin array also features filament buckling and straightening events.These observations indicate a mechanism inconsistent with treadmilling.Instead, cortical actin filament dynamics resemble the stochastic dynamics of an in vitro biomimetic system for actin assembly.

View Article: PubMed Central - PubMed

Affiliation: Department of Biological Sciences, Hansen Life Sciences Research Building, Purdue University, West Lafayette, IN 47907, USA.

ABSTRACT
Metazoan cells harness the power of actin dynamics to create cytoskeletal arrays that stimulate protrusions and drive intracellular organelle movements. In plant cells, the actin cytoskeleton is understood to participate in cell elongation; however, a detailed description and molecular mechanism(s) underpinning filament nucleation, growth, and turnover are lacking. Here, we use variable-angle epifluorescence microscopy (VAEM) to examine the organization and dynamics of the cortical cytoskeleton in growing and nongrowing epidermal cells. One population of filaments in the cortical array, which most likely represent single actin filaments, is randomly oriented and highly dynamic. These filaments grow at rates of 1.7 microm/s, but are generally short-lived. Instead of depolymerization at their ends, actin filaments are disassembled by severing activity. Remodeling of the cortical actin array also features filament buckling and straightening events. These observations indicate a mechanism inconsistent with treadmilling. Instead, cortical actin filament dynamics resemble the stochastic dynamics of an in vitro biomimetic system for actin assembly.

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The cortical actin array is remodeled continuously. Representative epidermal cell from a 5-d-old, dark-grown hypocotyl expressing GFP-fABD2 was observed with time-lapse VAEM. Successive images were made at ∼3-s intervals and every third image is depicted. Actin filament behaviors such as rapid growth (open arrowheads), buckling and straightening (red dots and asterisk), and severing activity (arrows) are marked. Collectively, this dynamic actin behavior resulted in rather short filament lifetimes (<30 s) and constant remodeling of the cortical array. Time points indicate the elapsed time from start of video sequence. See also Video 2 (available at http://www.jcb.org/cgi/content/full/jcb.200806185/DC1) for the full time-lapse series. Bar, 2 µm.
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fig1: The cortical actin array is remodeled continuously. Representative epidermal cell from a 5-d-old, dark-grown hypocotyl expressing GFP-fABD2 was observed with time-lapse VAEM. Successive images were made at ∼3-s intervals and every third image is depicted. Actin filament behaviors such as rapid growth (open arrowheads), buckling and straightening (red dots and asterisk), and severing activity (arrows) are marked. Collectively, this dynamic actin behavior resulted in rather short filament lifetimes (<30 s) and constant remodeling of the cortical array. Time points indicate the elapsed time from start of video sequence. See also Video 2 (available at http://www.jcb.org/cgi/content/full/jcb.200806185/DC1) for the full time-lapse series. Bar, 2 µm.

Mentions: In contrast to the orderly and predictable behavior of cortical microtubules, actin filaments visualized with GFP-fABD2 were extremely dynamic, producing a randomly organized and continuously rearranging cortical array (Videos 2 and 3, available at http://www.jcb.org/cgi/content/full/jcb.200806185/DC1). Overlaying two consecutive images separated by 3 s revealed mostly randomly oriented and convoluted actin filaments that changed positions, in addition to a few rigid and static actin filaments (Fig. S2 C, bottom). A montage and time-lapse video of another representative cell, with individual frames captured at ∼3-s intervals for a period of >5 min, reveals further aspects of actin filament behavior (Fig. 1; Video 2). Actin filaments that we identified as being single (see below) were oriented at a wide range of angles with respect to the cell's long axis, whereas stiffer, straighter filament bundles or cables were mostly oriented longitudinally. Actin filaments typically had a convoluted appearance that changed from frame to frame, indicating extensive buckling and straightening. New actin filaments appeared randomly and elongated rapidly from one end. Most individual filaments could rarely be tracked for >30 s with disappearance a consequence of severing activity. We detail the quantification of these and other aspects of cortical actin filament dynamics in the following sections.


Actin filament dynamics are dominated by rapid growth and severing activity in the Arabidopsis cortical array.

Staiger CJ, Sheahan MB, Khurana P, Wang X, McCurdy DW, Blanchoin L - J. Cell Biol. (2009)

The cortical actin array is remodeled continuously. Representative epidermal cell from a 5-d-old, dark-grown hypocotyl expressing GFP-fABD2 was observed with time-lapse VAEM. Successive images were made at ∼3-s intervals and every third image is depicted. Actin filament behaviors such as rapid growth (open arrowheads), buckling and straightening (red dots and asterisk), and severing activity (arrows) are marked. Collectively, this dynamic actin behavior resulted in rather short filament lifetimes (<30 s) and constant remodeling of the cortical array. Time points indicate the elapsed time from start of video sequence. See also Video 2 (available at http://www.jcb.org/cgi/content/full/jcb.200806185/DC1) for the full time-lapse series. Bar, 2 µm.
© Copyright Policy - openaccess
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC2654301&req=5

fig1: The cortical actin array is remodeled continuously. Representative epidermal cell from a 5-d-old, dark-grown hypocotyl expressing GFP-fABD2 was observed with time-lapse VAEM. Successive images were made at ∼3-s intervals and every third image is depicted. Actin filament behaviors such as rapid growth (open arrowheads), buckling and straightening (red dots and asterisk), and severing activity (arrows) are marked. Collectively, this dynamic actin behavior resulted in rather short filament lifetimes (<30 s) and constant remodeling of the cortical array. Time points indicate the elapsed time from start of video sequence. See also Video 2 (available at http://www.jcb.org/cgi/content/full/jcb.200806185/DC1) for the full time-lapse series. Bar, 2 µm.
Mentions: In contrast to the orderly and predictable behavior of cortical microtubules, actin filaments visualized with GFP-fABD2 were extremely dynamic, producing a randomly organized and continuously rearranging cortical array (Videos 2 and 3, available at http://www.jcb.org/cgi/content/full/jcb.200806185/DC1). Overlaying two consecutive images separated by 3 s revealed mostly randomly oriented and convoluted actin filaments that changed positions, in addition to a few rigid and static actin filaments (Fig. S2 C, bottom). A montage and time-lapse video of another representative cell, with individual frames captured at ∼3-s intervals for a period of >5 min, reveals further aspects of actin filament behavior (Fig. 1; Video 2). Actin filaments that we identified as being single (see below) were oriented at a wide range of angles with respect to the cell's long axis, whereas stiffer, straighter filament bundles or cables were mostly oriented longitudinally. Actin filaments typically had a convoluted appearance that changed from frame to frame, indicating extensive buckling and straightening. New actin filaments appeared randomly and elongated rapidly from one end. Most individual filaments could rarely be tracked for >30 s with disappearance a consequence of severing activity. We detail the quantification of these and other aspects of cortical actin filament dynamics in the following sections.

Bottom Line: Remodeling of the cortical actin array also features filament buckling and straightening events.These observations indicate a mechanism inconsistent with treadmilling.Instead, cortical actin filament dynamics resemble the stochastic dynamics of an in vitro biomimetic system for actin assembly.

View Article: PubMed Central - PubMed

Affiliation: Department of Biological Sciences, Hansen Life Sciences Research Building, Purdue University, West Lafayette, IN 47907, USA.

ABSTRACT
Metazoan cells harness the power of actin dynamics to create cytoskeletal arrays that stimulate protrusions and drive intracellular organelle movements. In plant cells, the actin cytoskeleton is understood to participate in cell elongation; however, a detailed description and molecular mechanism(s) underpinning filament nucleation, growth, and turnover are lacking. Here, we use variable-angle epifluorescence microscopy (VAEM) to examine the organization and dynamics of the cortical cytoskeleton in growing and nongrowing epidermal cells. One population of filaments in the cortical array, which most likely represent single actin filaments, is randomly oriented and highly dynamic. These filaments grow at rates of 1.7 microm/s, but are generally short-lived. Instead of depolymerization at their ends, actin filaments are disassembled by severing activity. Remodeling of the cortical actin array also features filament buckling and straightening events. These observations indicate a mechanism inconsistent with treadmilling. Instead, cortical actin filament dynamics resemble the stochastic dynamics of an in vitro biomimetic system for actin assembly.

Show MeSH
Related in: MedlinePlus