The nuclei of early syncytial Drosophila embryos migrate dramatically toward the poles. The cellular mechanisms driving this process, called axial expansion, are unclear, but myosin II activity is required. By following regulatory myosin light chain (RLC)–green fluorescent protein dynamics in living embryos, we observed cycles of myosin recruitment to the cortex synchronized with mitotic cycles. Cortical myosin is first seen in a patch at the anterocentral part of the embryo at cycle 4. With each succeeding cycle, the patch expands poleward, dispersing at the beginning of each mitosis and reassembling at the end of telophase. Each cycle of actin and myosin recruitment is accompanied by a cortical contraction. The cortical myosin cycle does not require microtubules but correlates inversely with Cdc2/cyclinB (mitosis-promoting factor) activity. A mutant RLC lacking inhibitory phosphorylation sites was fully functional with no effect on the cortical myosin cycle, indicating that Cdc2 must be modulating myosin activity by some other mechanism. An inhibitor of Rho kinase blocks the cortical myosin recruitment cycles and provokes a concomitant failure of axial expansion. These studies suggest a model in which cycles of myosin-mediated contraction and relaxation, tightly linked to Cdc2 and Rho kinase activity, are directly responsible for the axial expansion of the syncytial nuclei.
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8 July 2002
Article|
July 08 2002
Cortical recruitment of nonmuscle myosin II in early syncytial Drosophila embryos : its role in nuclear axial expansion and its regulation by Cdc2 activity
Anne Royou,
Anne Royou
1Centre National de la Recherche Scientifique, Centre de Génétique Moléculaire, 91198 Gif-sur-Yvette, France
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William Sullivan,
William Sullivan
2Department of Molecular, Cell, and Developmental Biology, Sinsheimer Labs, University of California, Santa Cruz, CA 95064
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Roger Karess
Roger Karess
1Centre National de la Recherche Scientifique, Centre de Génétique Moléculaire, 91198 Gif-sur-Yvette, France
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Anne Royou
1Centre National de la Recherche Scientifique, Centre de Génétique Moléculaire, 91198 Gif-sur-Yvette, France
William Sullivan
2Department of Molecular, Cell, and Developmental Biology, Sinsheimer Labs, University of California, Santa Cruz, CA 95064
Roger Karess
1Centre National de la Recherche Scientifique, Centre de Génétique Moléculaire, 91198 Gif-sur-Yvette, France
Address correspondence to Roger E. Karess, Centre de Génétique Moléculaire, Centre National de la Recherche Scientifique, Ave de la Terrasse, 91198 Gif sur Yvette, France. Tel.: 33-1-69-82-32-25. Fax: 33-1-69-82-31-50. E-mail: [email protected]
The online version of this article contains supplemental material.
*
Abbreviations used in this paper: A-P, anterior-posterior; Drok, Drosophila rho kinase; GFP, green fluorescent protein; GST, glutathione S-transferase; MHC, myosin heavy chain; MLCK, myosin light chain kinase; RLC, regulatory myosin light chain; TLCM, time-lapse confocal microscopy.
Received:
March 29 2002
Revision Received:
May 15 2002
Accepted:
May 16 2002
Online ISSN: 1540-8140
Print ISSN: 0021-9525
The Rockefeller University Press
2002
J Cell Biol (2002) 158 (1): 127–137.
Article history
Received:
March 29 2002
Revision Received:
May 15 2002
Accepted:
May 16 2002
Citation
Anne Royou, William Sullivan, Roger Karess; Cortical recruitment of nonmuscle myosin II in early syncytial Drosophila embryos : its role in nuclear axial expansion and its regulation by Cdc2 activity . J Cell Biol 8 July 2002; 158 (1): 127–137. doi: https://doi.org/10.1083/jcb.200203148
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