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Engineering Approaches to Biomolecular Motors: From in vitro to in vivo Friday Speaker Abstracts
34
Self-organization of Active Cytoskeletal Networks in a Cell-sized Confined Space
Shin'ichi Ishiwata
, Makito Miyazaki, Masataka Chiba, Kazuya Suzuki.
Waseda University, Tokyo, Japan.
Biomolecular machines generally fulfil their functions within a cell, which is a microscopic
space confined by a deformable cell membrane. Among the biomolecular machines, bio-motile
systems composed of molecular motors and cytoskeleton (actin filaments and microtubules) are
exceptional in the sense that they produce force to change the cell shape. Conversely, the
dynamics of bio-motile systems will be influenced by the size and shape of cell, and the physical
properties of the cell membrane. To understand the relationship between the structure/function of
the bio-motile systems and the physical properties of cell membrane, i.e., to understand the role
of cell membrane as a boundary condition for the dynamics of bio-motile systems, we have
examined how the spatio-temporal dynamics of the bio-motile systems are realized within a cell-
sized space confined by a phospholipid membrane. In the present talk, two to three topics will be
introduced. The first topic will be the demonstration that polymerization of actin filaments inside
a cell-sized water-in-oil droplet surrounded by a monolayer phospholipid membrane induces
spontaneous formation of a ring-shaped contractile actin bundle in the presence of appropriate
amount of myosin molecules and bundling factors. This strongly suggests that the spherical
boundary condition promotes the formation of contractile ring. The second topic will be that
when cytoplasmic extracts prepared from Xenopus eggs are encapsulated in a droplet,
microtubule network induced accumulation of cellular components and rotational cytoplasmic
flow, depending on the level of dynein activity. Those results were obtained in a cell-sized
confinement surrounded by a monolayer of phospholipids self-organized in oil. When those
phenomena are reproduced in a giant unilamellar liposome prepared by the inverted emulsion
method, the present experimental system is expected to be useful for designing a model system
of artificial cells.