TY - JOUR
T1 - Formation and maintenance of tubular membrane projections require mechanical force, but their elongation and shortening do not require additional force
AU - Inaba, Takehiko
AU - Ishijima, Akihiko
AU - Honda, Makoto
AU - Nomura, Fumimasa
AU - Takiguchi, Kingo
AU - Hotani, Hirokazu
N1 - Funding Information:
This research was supported by the Ministry of Education, Science, Sports and Culture of Japan, Grants-in-Aid for Scientific Research.
PY - 2005/4/29
Y1 - 2005/4/29
N2 - Living cells develop their own characteristic shapes depending on their physiological functions, and their morphologies are based on the mechanical characteristics of the cytoskeleton and of membranes. To investigate the role of lipid membranes in morphogenesis, we constructed a simple system that can manipulate liposomes and measure the forces required to transform their shapes. Two polystyrene beads (1 μm in diameter) were encapsulated in giant liposomes and were manipulated using double-beam laser tweezers. Without any specific interaction between the lipid membrane and beads, mechanical forces could be applied to the liposome membrane from the inside. Spherical liposomes transformed into a lemon shape with increasing tension, and tubular membrane projections were subsequently generated in the tips at either end. This process is similar to the liposomal transformation caused by elongation of encapsulated cytoskeletons. In the elongation stage of lemon-shaped liposomes, the force required for the transformation became larger as the end-to-end length increased. Just before the tubular membrane was generated, the force reached the maximum strength (∼11 pN). However, immediately after the tubular membrane developed, the force suddenly decreased and was maintained at a constant strength (∼4 pN) that was independent of further tube elongation or shortening, even though there was no excess membrane reservoir as occurs in living cells. When the tube length was shortened to ∼2 μm, the liposome reversed to a lemon shape and the force temporarily increased (to ∼7 pN). These results indicate that the simple application of mechanical force is sufficient to form a protrusion in a membrane, that a critical force and length is needed to form and to maintain the protrusion, and suggest that the lipid bilayer itself has the ability to buffer the membrane tension.
AB - Living cells develop their own characteristic shapes depending on their physiological functions, and their morphologies are based on the mechanical characteristics of the cytoskeleton and of membranes. To investigate the role of lipid membranes in morphogenesis, we constructed a simple system that can manipulate liposomes and measure the forces required to transform their shapes. Two polystyrene beads (1 μm in diameter) were encapsulated in giant liposomes and were manipulated using double-beam laser tweezers. Without any specific interaction between the lipid membrane and beads, mechanical forces could be applied to the liposome membrane from the inside. Spherical liposomes transformed into a lemon shape with increasing tension, and tubular membrane projections were subsequently generated in the tips at either end. This process is similar to the liposomal transformation caused by elongation of encapsulated cytoskeletons. In the elongation stage of lemon-shaped liposomes, the force required for the transformation became larger as the end-to-end length increased. Just before the tubular membrane was generated, the force reached the maximum strength (∼11 pN). However, immediately after the tubular membrane developed, the force suddenly decreased and was maintained at a constant strength (∼4 pN) that was independent of further tube elongation or shortening, even though there was no excess membrane reservoir as occurs in living cells. When the tube length was shortened to ∼2 μm, the liposome reversed to a lemon shape and the force temporarily increased (to ∼7 pN). These results indicate that the simple application of mechanical force is sufficient to form a protrusion in a membrane, that a critical force and length is needed to form and to maintain the protrusion, and suggest that the lipid bilayer itself has the ability to buffer the membrane tension.
KW - Giant liposome
KW - Laser tweezers
KW - Membrane morphogenesis
KW - Membrane tether
KW - Optical microscopy
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U2 - 10.1016/j.jmb.2005.02.060
DO - 10.1016/j.jmb.2005.02.060
M3 - Article
C2 - 15811371
AN - SCOPUS:16244390882
VL - 348
SP - 325
EP - 333
JO - Journal of Molecular Biology
JF - Journal of Molecular Biology
SN - 0022-2836
IS - 2
ER -