Journal Article

Hydrostatic pressure and the actomyosin cortex drive mitotic cell rounding

Helenius, Jonne, Ramanathan, Subramanian P., Muller, Daniel J., Toyoda, Yusuke, Stewart, Martin P., Hyman, Anthony A.

2011

Overview

What makes cells go round Forces that drive cell shape changes are fundamental to development. During mitosis, adherent cells change from a flattened to rounded morphology, and this is thought to be necessary for the geometric requirements of cell division. Stewart et al . study the forces that drive this shape change. They find that the mitotic rounding force depends both on the actomyosin cytoskeleton and the cell's ability to regulate osmolarity. The rounding force is generated by osmotic pressure, and the actomyosin cortex maintains this rounding pressure against external forces. These results support the idea that in animal cells, the actomyosin cortex behaves as an internal cell wall, directing osmotic expansion to control cell shape. During mitosis, adherent cells change from a flattened to a rounded morphology, and this is thought to be necessary for the geometric requirements of cell division. Here, the forces that drive this shape change are studied. Mitotic rounding force depends both on the actomyosin cytoskeleton and the cell's ability to regulate osmolarity. The rounding force is generated by osmotic pressure and the actomyosin cortex maintains this rounding pressure against external forces. These results support the idea that in animal cells, the actomyosin cortex behaves like an internal cell wall that directs osmotic expansion to control cell shape. During mitosis, adherent animal cells undergo a drastic shape change, from essentially flat to round 1 , 2 , 3 . Mitotic cell rounding is thought to facilitate organization within the mitotic cell and be necessary for the geometric requirements of division 4 , 5 , 6 , 7 . However, the forces that drive this shape change remain poorly understood in the presence of external impediments, such as a tissue environment 2 . Here we use cantilevers to track cell rounding force and volume. We show that cells have an outward rounding force, which increases as cells enter mitosis. We find that this mitotic rounding force depends both on the actomyosin cytoskeleton and the cells’ ability to regulate osmolarity. The rounding force itself is generated by an osmotic pressure. However, the actomyosin cortex is required to maintain this rounding force against external impediments. Instantaneous disruption of the actomyosin cortex leads to volume increase, and stimulation of actomyosin contraction leads to volume decrease. These results show that in cells, osmotic pressure is balanced by inwardly directed actomyosin cortex contraction. Thus, by locally modulating actomyosin-cortex-dependent surface tension and globally regulating osmotic pressure, cells can control their volume, shape and mechanical properties.

• Publisher: Nature Publishing Group UK,Nature Publishing Group
• Subject: Actomyosin - metabolism / Animals / Biological and medical sciences / Cell cycle / Cell cycle, cell proliferation / Cell physiology / Cell Shape - drug effects / Cell Shape - physiology / Cell Size - drug effects / Cellular biology / Chromosomes / Cytochalasin D - pharmacology / Cytoskeleton / Cytoskeleton - drug effects / Cytoskeleton - metabolism / Experiments / Fundamental and applied biological sciences. Psychology / HeLa Cells / Humanities and Social Sciences / Humans / Hydrostatic Pressure / letter / Methods / Microscopy / Microscopy, Atomic Force / Mitosis / Models, Biological / Molecular and cellular biology / multidisciplinary / Observations / Osmolar Concentration / Osmotic Pressure / Prophase / Proteins / Science / Surface tension