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Two-dimensional periodic texture of actin filaments formed upon drying

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ABSTRACT

We found that a solution of actin filaments can form a periodic texture in the process of drying on a flat glass surface in the air; the periodic texture was composed of smooth meandering bundles of actin filaments. We also found that a branched salt crystal grows in the space between the meandering bundles of actin filaments. The distance between the adjacent striae (striation period) in the resulting dried two-dimensional pattern of striation decreased from about 50 to 2 μm, as the ambient temperature was increased from 4 to 40°C at 1 mg/ml actin, and showed an increasing tendency from a few to several tens μm with the increase in the initial concentration of actin filaments from 0.6 to 2.0mg/ml at room temperature. As the speed of drying is increased at a certain temperature, the striation period was also found to decrease. We propose that the formation of the two-dimensional striation pattern of bundles of actin filaments is the result of condensation of proteins due to dehydration, and suggest that the solvent flow from the center to the periphery of the sample causes the meandering of actin filaments.

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Schematic showing how the striation pattern is formed in F-actin solution during the process of drying. (a) Cross-sectional view of the shape of F-actin solution spread on glass slide surface, showing the direction of flow due to the evaporation of water. The solid curve shows the equilibrium shape of the solution obtained without evaporation of water. Because the evaporation uniformly occurs from the surface, the surface shape deviates from the equilibrium shape, as shown by the dashed curve. This results in the outward flow of solvent in one direction but not in a convectional manner. (b, c), The wavy shape of F-actin bundles and the periodic striation patterns (b) for flexible bundles or in the case of fast drying and (c) for rigid bundles or in the case of slow drying. Solid curves schematically show the F-actin bundles. Vertical dark bands, correspond to the black lines observed in dried samples under the microscope. Here, the shape of the F-actin bundles is assumed to be sinusoidal, so that the period p is uniform. (d) The striation pattern obtained by assuming the asymmetric wavy shape of the F-actin bundles, seems to be more realistic. In the present study, the striation period was defined as the average separation between the adjacent black lines, irrespective of the repetitive long (p1) and short (p2) periods. For more details, see the text.
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f10-7_11: Schematic showing how the striation pattern is formed in F-actin solution during the process of drying. (a) Cross-sectional view of the shape of F-actin solution spread on glass slide surface, showing the direction of flow due to the evaporation of water. The solid curve shows the equilibrium shape of the solution obtained without evaporation of water. Because the evaporation uniformly occurs from the surface, the surface shape deviates from the equilibrium shape, as shown by the dashed curve. This results in the outward flow of solvent in one direction but not in a convectional manner. (b, c), The wavy shape of F-actin bundles and the periodic striation patterns (b) for flexible bundles or in the case of fast drying and (c) for rigid bundles or in the case of slow drying. Solid curves schematically show the F-actin bundles. Vertical dark bands, correspond to the black lines observed in dried samples under the microscope. Here, the shape of the F-actin bundles is assumed to be sinusoidal, so that the period p is uniform. (d) The striation pattern obtained by assuming the asymmetric wavy shape of the F-actin bundles, seems to be more realistic. In the present study, the striation period was defined as the average separation between the adjacent black lines, irrespective of the repetitive long (p1) and short (p2) periods. For more details, see the text.

Mentions: Figure 2 shows the detailed structure which was formed after drying at various places from the peripheral area (Fig. 2a) to the central area (Fig. 2f). Randomly oriented F-actin bundles were frequently observed at the periphery of the dried sample (Fig. 2a); these were caused by the turbulent flow produced when the solution was initially dropped. The striation region of F-actin bundles (Fig. 2b–e) appeared about 0.5 mm within the peripheral region. As the evaporation proceeded, branched salt crystals started to grow along the wavy F-actin bundles (Fig. 2c–e). Then the branched salt crystals gradually diminished. Note that the branching of the salt crystals consistently occurred at the black region of the striation (see Fig. 7b, in the white region the density of actin bundles seems to be low as indicated by the low density of CBB staining; also see the schematic illustration shown in Fig. 10). This result implies that the salt crystal formation preferentially occurs within a space where the protein concentration is low. Approaching the central region, thick salt crystals appeared and an irregular striation-like structure began to be formed (Fig. 2f). Finally, salt crystals grew at the center of the sample (Fig. 2g).


Two-dimensional periodic texture of actin filaments formed upon drying
Schematic showing how the striation pattern is formed in F-actin solution during the process of drying. (a) Cross-sectional view of the shape of F-actin solution spread on glass slide surface, showing the direction of flow due to the evaporation of water. The solid curve shows the equilibrium shape of the solution obtained without evaporation of water. Because the evaporation uniformly occurs from the surface, the surface shape deviates from the equilibrium shape, as shown by the dashed curve. This results in the outward flow of solvent in one direction but not in a convectional manner. (b, c), The wavy shape of F-actin bundles and the periodic striation patterns (b) for flexible bundles or in the case of fast drying and (c) for rigid bundles or in the case of slow drying. Solid curves schematically show the F-actin bundles. Vertical dark bands, correspond to the black lines observed in dried samples under the microscope. Here, the shape of the F-actin bundles is assumed to be sinusoidal, so that the period p is uniform. (d) The striation pattern obtained by assuming the asymmetric wavy shape of the F-actin bundles, seems to be more realistic. In the present study, the striation period was defined as the average separation between the adjacent black lines, irrespective of the repetitive long (p1) and short (p2) periods. For more details, see the text.
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Related In: Results  -  Collection

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f10-7_11: Schematic showing how the striation pattern is formed in F-actin solution during the process of drying. (a) Cross-sectional view of the shape of F-actin solution spread on glass slide surface, showing the direction of flow due to the evaporation of water. The solid curve shows the equilibrium shape of the solution obtained without evaporation of water. Because the evaporation uniformly occurs from the surface, the surface shape deviates from the equilibrium shape, as shown by the dashed curve. This results in the outward flow of solvent in one direction but not in a convectional manner. (b, c), The wavy shape of F-actin bundles and the periodic striation patterns (b) for flexible bundles or in the case of fast drying and (c) for rigid bundles or in the case of slow drying. Solid curves schematically show the F-actin bundles. Vertical dark bands, correspond to the black lines observed in dried samples under the microscope. Here, the shape of the F-actin bundles is assumed to be sinusoidal, so that the period p is uniform. (d) The striation pattern obtained by assuming the asymmetric wavy shape of the F-actin bundles, seems to be more realistic. In the present study, the striation period was defined as the average separation between the adjacent black lines, irrespective of the repetitive long (p1) and short (p2) periods. For more details, see the text.
Mentions: Figure 2 shows the detailed structure which was formed after drying at various places from the peripheral area (Fig. 2a) to the central area (Fig. 2f). Randomly oriented F-actin bundles were frequently observed at the periphery of the dried sample (Fig. 2a); these were caused by the turbulent flow produced when the solution was initially dropped. The striation region of F-actin bundles (Fig. 2b–e) appeared about 0.5 mm within the peripheral region. As the evaporation proceeded, branched salt crystals started to grow along the wavy F-actin bundles (Fig. 2c–e). Then the branched salt crystals gradually diminished. Note that the branching of the salt crystals consistently occurred at the black region of the striation (see Fig. 7b, in the white region the density of actin bundles seems to be low as indicated by the low density of CBB staining; also see the schematic illustration shown in Fig. 10). This result implies that the salt crystal formation preferentially occurs within a space where the protein concentration is low. Approaching the central region, thick salt crystals appeared and an irregular striation-like structure began to be formed (Fig. 2f). Finally, salt crystals grew at the center of the sample (Fig. 2g).

View Article: PubMed Central - PubMed

ABSTRACT

We found that a solution of actin filaments can form a periodic texture in the process of drying on a flat glass surface in the air; the periodic texture was composed of smooth meandering bundles of actin filaments. We also found that a branched salt crystal grows in the space between the meandering bundles of actin filaments. The distance between the adjacent striae (striation period) in the resulting dried two-dimensional pattern of striation decreased from about 50 to 2 μm, as the ambient temperature was increased from 4 to 40°C at 1 mg/ml actin, and showed an increasing tendency from a few to several tens μm with the increase in the initial concentration of actin filaments from 0.6 to 2.0mg/ml at room temperature. As the speed of drying is increased at a certain temperature, the striation period was also found to decrease. We propose that the formation of the two-dimensional striation pattern of bundles of actin filaments is the result of condensation of proteins due to dehydration, and suggest that the solvent flow from the center to the periphery of the sample causes the meandering of actin filaments.

No MeSH data available.


Related in: MedlinePlus