- Email: [email protected]
Tying up molecules
FORUM
comment
factors other than the Arp2/3 complex might nucleate actin polymerization in cells. Finally, although it is becoming increasingly clear that regulating actin nucleation is an important facet in controlling polymerization in cells, nucleation is only one of several important control points in the cycle of actin assembly. Filament elongation must also be modulated by the activities of sequestering proteins, barbed-endcapping proteins, and other less-characterized factors. In addition to its role in regulating nucleation, Cdc42 has been proposed to facilitate filament elongation39, suggesting there might be a fundamental link between the two processes. A more complete understanding of the role of actin polymerization in cell-shape change and locomotion awaits further determination of how nucleation is integrated with other processes such as filament elongation, crosslinking and depolymerization. References 1 Machesky, L. M. and Gould, K. L. (1999) Curr. Opin. Cell Biol. 11, 117–121 2 Mullins, R. D., Heuser, J. A. and Pollard, T. D. (1998) Proc. Natl. Acad. Sci. U. S. A. 95, 6181–6186 3 Welch, M. D. et al. (1998) Science 281, 105–108 4 Welch, M. D., Iwamatsu, A. and Mitchison, T. J. (1997) Nature 385, 265–269 5 Dramsi, S. and Cossart, P. (1998) Annu. Rev. Cell Dev. Biol. 14, 137–166 6 Bailly, M. et al. (1999) J. Cell Biol. 145, 331–345 7 Svitkina, T. M. and Borisy, G. G. (1999) J. Cell Biol. 145, 1009–1026 8 Svitkina, T. M. et al. (1997) J. Cell Biol. 139, 397–415 9 Machesky, L. M. et al. (1997) Biochem. J. 328, 105–112 10 Weiner, O. et al. (1999) Nat. Cell Biol. 1, 75–81 11 Ma, L., Rohatgi, R. and Kirschner, M. W. (1998) Proc. Natl.
12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40
Acad. Sci. U. S. A. 95, 15362–15367 Mullins, R. D. and Pollard, T. D. (1999) Curr. Biol. 9, 405–415 Aspenstrom, P. (1999) Exp. Cell Res. 246, 20–25 Abo, A. (1998) Cell. Mol. Life Sci. 54, 1145–1153 Ramesh, N. et al. (1999) Trends Cell Biol. 9, 15–19 Winter, D. et al. (1997) Curr. Biol. 7, 519–529 Machesky, L. M. and Insall, R. H. (1998) Curr. Biol. 8, 1347–1356 Rohatgi, R. et al. (1999) Cell 97, 221–231 Winter, D., Lechler, T. and Li, R. (1999) Curr. Biol. 9, 501–504 Snapper, S. B. et al. (1998) Immunity 9, 81–91 Li, R. (1997) J. Cell Biol. 136, 649–658 Naqvi, S. N. et al. (1998) Curr. Biol. 8, 959–962 Bear, J. E., Rawls, J. F. and Saxe, C. L., III (1998) J. Cell Biol. 142, 1325–1335 Zicha, D. et al. (1998) Br. J. Haematol. 101, 659–665 Miki, H., Suetsugu, S. and Takenawa, T. (1998) EMBO J. 17, 6932–6941 Symons, M. et al. (1996) Cell 84, 723–734 Castellano, F. et al. (1999) Curr. Biol. 9, 351–360 Niebuhr, K. et al. (1997) EMBO J. 16, 5433–5444 Prehoda, K. E., Lee, D. J. and Lim, W. A. (1999) Cell 97, 471–480 Fedorov, A. A. et al. (1999) Nat. Struct. Biol. 6, 661–665 Suetsugu, S., Miki, H. and Takenawa, T. (1998) EMBO J. 17, 6516–6526 Miki, H. and Takenawa, T. (1998) –iochem. Biophys. Res. Commun. 243, 73–78 Machesky, L. (1999) Nat. Cell Biol. 1, E29–E31 Miki, H. et al. (1998) Nature 391, 93–96 Acknowledgements Moreau, V. and Way, M. (1998) FEBS Lett. 427, 353–356 I thank Yarar, D. et al. (1999) Curr. Biol. 9, 555–558 Machesky, L. M. et al. (1999) Proc. Natl. Acad. Sci. U. S. A. 96, Rebecca Heald, Justin Skoble and 3739–3744 Defne Yarar for Suzuki, T. et al. (1998) EMBO J. 17, 2767–2776 helpful discussions Zigmond, S. H. et al. (1998) J. Cell Biol. 142, 1001–1012 and comments on the Welch, M. D. et al. (1997) J. Cell Biol. 138, 375–384 manuscript.
Pictures in cell biology: Tying up molecules
FIGURE 1 Tying a knot in a DNA molecule. A DNA molecule stained with POPO-3 was attached to two beads, and then movement of the beads using optical tweezers was used to generate various types of conformation, including knots, in the DNA molecule. Images 3–7 are accompanied by explanatory drawings depicting the conformation shown. The paper1 contains a similar set of images for actin, and other types of knot in DNA molecules. Bar, 10 mm.
A recent paper 1 took manipulation of molecules with optical tweezers to a new level by showing that it is possible to tie knots in both actin filaments and DNA molecules (Fig. 1). Arai et al. attached polystyrene beads to the polymers, then used optical tweezers to manipulate these beads and hence the polymers themselves. In addition to tying knots, they recorded the tensile strength and flexibility of both the actin filaments and DNA molecules. As well as being an entertaining exercise, this approach has
trends in CELL BIOLOGY (Vol. 9) November 1999
further practical applications. Tying a knot in a linear polymer generates a stable curvature that could be used as a basis for experimentation on, for example, the binding of associated proteins to curved versus straight polymer. Conceivably, knotting of such molecules could also be used to perturb cellular structure and observe the resulting effects. Reference 1 Arai, Y. et al. (1999) Nature 399, 446–448
Produced in collaboration with Yoshie Harada, Dept of Physics, Faculty of Science and Technology, Keio University, Hiyoshi 3-14-1, Kohoku-ku, Yokohama, 223 8522, Japan.
427
comment
factors other than the Arp2/3 complex might nucleate actin polymerization in cells. Finally, although it is becoming increasingly clear that regulating actin nucleation is an important facet in controlling polymerization in cells, nucleation is only one of several important control points in the cycle of actin assembly. Filament elongation must also be modulated by the activities of sequestering proteins, barbed-endcapping proteins, and other less-characterized factors. In addition to its role in regulating nucleation, Cdc42 has been proposed to facilitate filament elongation39, suggesting there might be a fundamental link between the two processes. A more complete understanding of the role of actin polymerization in cell-shape change and locomotion awaits further determination of how nucleation is integrated with other processes such as filament elongation, crosslinking and depolymerization. References 1 Machesky, L. M. and Gould, K. L. (1999) Curr. Opin. Cell Biol. 11, 117–121 2 Mullins, R. D., Heuser, J. A. and Pollard, T. D. (1998) Proc. Natl. Acad. Sci. U. S. A. 95, 6181–6186 3 Welch, M. D. et al. (1998) Science 281, 105–108 4 Welch, M. D., Iwamatsu, A. and Mitchison, T. J. (1997) Nature 385, 265–269 5 Dramsi, S. and Cossart, P. (1998) Annu. Rev. Cell Dev. Biol. 14, 137–166 6 Bailly, M. et al. (1999) J. Cell Biol. 145, 331–345 7 Svitkina, T. M. and Borisy, G. G. (1999) J. Cell Biol. 145, 1009–1026 8 Svitkina, T. M. et al. (1997) J. Cell Biol. 139, 397–415 9 Machesky, L. M. et al. (1997) Biochem. J. 328, 105–112 10 Weiner, O. et al. (1999) Nat. Cell Biol. 1, 75–81 11 Ma, L., Rohatgi, R. and Kirschner, M. W. (1998) Proc. Natl.
12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40
Acad. Sci. U. S. A. 95, 15362–15367 Mullins, R. D. and Pollard, T. D. (1999) Curr. Biol. 9, 405–415 Aspenstrom, P. (1999) Exp. Cell Res. 246, 20–25 Abo, A. (1998) Cell. Mol. Life Sci. 54, 1145–1153 Ramesh, N. et al. (1999) Trends Cell Biol. 9, 15–19 Winter, D. et al. (1997) Curr. Biol. 7, 519–529 Machesky, L. M. and Insall, R. H. (1998) Curr. Biol. 8, 1347–1356 Rohatgi, R. et al. (1999) Cell 97, 221–231 Winter, D., Lechler, T. and Li, R. (1999) Curr. Biol. 9, 501–504 Snapper, S. B. et al. (1998) Immunity 9, 81–91 Li, R. (1997) J. Cell Biol. 136, 649–658 Naqvi, S. N. et al. (1998) Curr. Biol. 8, 959–962 Bear, J. E., Rawls, J. F. and Saxe, C. L., III (1998) J. Cell Biol. 142, 1325–1335 Zicha, D. et al. (1998) Br. J. Haematol. 101, 659–665 Miki, H., Suetsugu, S. and Takenawa, T. (1998) EMBO J. 17, 6932–6941 Symons, M. et al. (1996) Cell 84, 723–734 Castellano, F. et al. (1999) Curr. Biol. 9, 351–360 Niebuhr, K. et al. (1997) EMBO J. 16, 5433–5444 Prehoda, K. E., Lee, D. J. and Lim, W. A. (1999) Cell 97, 471–480 Fedorov, A. A. et al. (1999) Nat. Struct. Biol. 6, 661–665 Suetsugu, S., Miki, H. and Takenawa, T. (1998) EMBO J. 17, 6516–6526 Miki, H. and Takenawa, T. (1998) –iochem. Biophys. Res. Commun. 243, 73–78 Machesky, L. (1999) Nat. Cell Biol. 1, E29–E31 Miki, H. et al. (1998) Nature 391, 93–96 Acknowledgements Moreau, V. and Way, M. (1998) FEBS Lett. 427, 353–356 I thank Yarar, D. et al. (1999) Curr. Biol. 9, 555–558 Machesky, L. M. et al. (1999) Proc. Natl. Acad. Sci. U. S. A. 96, Rebecca Heald, Justin Skoble and 3739–3744 Defne Yarar for Suzuki, T. et al. (1998) EMBO J. 17, 2767–2776 helpful discussions Zigmond, S. H. et al. (1998) J. Cell Biol. 142, 1001–1012 and comments on the Welch, M. D. et al. (1997) J. Cell Biol. 138, 375–384 manuscript.
Pictures in cell biology: Tying up molecules
FIGURE 1 Tying a knot in a DNA molecule. A DNA molecule stained with POPO-3 was attached to two beads, and then movement of the beads using optical tweezers was used to generate various types of conformation, including knots, in the DNA molecule. Images 3–7 are accompanied by explanatory drawings depicting the conformation shown. The paper1 contains a similar set of images for actin, and other types of knot in DNA molecules. Bar, 10 mm.
A recent paper 1 took manipulation of molecules with optical tweezers to a new level by showing that it is possible to tie knots in both actin filaments and DNA molecules (Fig. 1). Arai et al. attached polystyrene beads to the polymers, then used optical tweezers to manipulate these beads and hence the polymers themselves. In addition to tying knots, they recorded the tensile strength and flexibility of both the actin filaments and DNA molecules. As well as being an entertaining exercise, this approach has
trends in CELL BIOLOGY (Vol. 9) November 1999
further practical applications. Tying a knot in a linear polymer generates a stable curvature that could be used as a basis for experimentation on, for example, the binding of associated proteins to curved versus straight polymer. Conceivably, knotting of such molecules could also be used to perturb cellular structure and observe the resulting effects. Reference 1 Arai, Y. et al. (1999) Nature 399, 446–448
Produced in collaboration with Yoshie Harada, Dept of Physics, Faculty of Science and Technology, Keio University, Hiyoshi 3-14-1, Kohoku-ku, Yokohama, 223 8522, Japan.
427