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Actin behavior in bulk cytoplasm is cell cycle regulated in early vertebrate embryos

Field, Christine M. and Wühr, Martin and Anderson, Graham A. and Kueh, Hao Yuan and Strickland, Devin and Mitchison, Timothy J. (2011) Actin behavior in bulk cytoplasm is cell cycle regulated in early vertebrate embryos. Journal of Cell Science, 124 (12). pp. 2086-2095. ISSN 0021-9533.

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The mechanical properties of cells change as they proceed through the cell cycle, primarily owing to regulation of actin and myosin II. Most models for cell mechanics focus on actomyosin in the cortex and ignore possible roles in bulk cytoplasm. We explored cell cycle regulation of bulk cytoplasmic actomyosin in Xenopus egg extracts, which is almost undiluted cytoplasm from unfertilized eggs. We observed dramatic gelation-contraction of actomyosin in mitotic (M phase) extract where Cdk1 activity is high, but not in interphase (I-phase) extract. In spread droplets, M-phase extract exhibited regular, periodic pulses of gelation-contraction a few minutes apart that continued for many minutes. Comparing actin nucleation, disassembly and myosin II activity between M-phase and I-phase extracts, we conclude that regulation of nucleation is likely to be the most important for cell cycle regulation. We then imaged F-actin in early zebrafish blastomeres using a GFP–Utrophin probe. Polymerization in bulk cytoplasm around vesicles increased dramatically during mitosis, consistent with enhanced nucleation. We conclude that F-actin polymerization in bulk cytoplasm is cell cycle regulated in early vertebrate embryos and discuss possible biological functions of this regulation.

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Additional Information:© 2011 The Company of Biologists Ltd. Accepted February 2, 2011. Advance Online Publication May 24, 2011. This work was supported by NIH GM023928. Early experiments were piloted by MBL Woods Hole Physiology Course students in 2006–2008. The MBP–Cyclin B Δ90 construct was a gift of Adrian Salic (HMS) and was expressed by Aaron Groen (HMS). Bill Brieher (U Illinois) provided labeled actin, actin binding/bundling proteins and valuable discussion. Paul Chang (MIT) and Aaron Groen provided HeLa cells and guidance on making concentrated extracts. Dyche Mullins (UCSF) provided the CA domain of scar1. David Burgess (Boston College) provided GFP–Utrophin. Sean Megason (HMS) helped with zebrafish husbandry and imaging. C.M.F. thanks Marc Kirschner for tolerance, support and happy frogs. Deposited in PMC for release after 6 months.
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Subject Keywords:Actin; Actomyosin; Embryo; Cell cycle
Issue or Number:12
Record Number:CaltechAUTHORS:20110610-113203970
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:23974
Deposited By: Jason Perez
Deposited On:10 Jun 2011 20:07
Last Modified:03 Oct 2019 02:51

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