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Biophys J, August 2000, p. 707-719, Vol. 79, No. 2

A Micromechanic Study of Cell Polarity and Plasma Membrane Cell Body Coupling in Dictyostelium

Rudolf Merkel,* Rudolf Simson,* Doris A. Simson,* Melanie Hohenadl,* Alexei Boulbitch,* Eva Wallraff,dagger and Erich Sackmann*

 *Fakultät für Physik, Lehrstuhl für Biophysik, Technische Universität München, D-85747 Garching, and  dagger Max-Planck-Institut für Biochemie, D-82152 Martinsried, Germany

We used micropipettes to aspirate leading and trailing edges of wild-type and mutant cells of Dictyostelium discoideum. Mutants were lacking either myosin II or talin, or both proteins simultaneously. Talin is a plasma membrane-associated protein important for the coupling between membrane and actin cortex, whereas myosin II is a cytoplasmic motor protein essential for the locomotion of Dictyostelium cells. Aspiration into the pipette occurred above a threshold pressure only. For all cells containing talin this threshold was significantly lower at the leading edge of an advancing cell as compared to its rear end, whereas we found no such difference in cells lacking talin. Wild-type and talin-deficient cells were able to retract from the pipette against an applied suction pressure. In these cells, retraction was preceded by an accumulation of myosin II in the tip of the aspirated cell lobe. Mutants lacking myosin II could not retract, even if the suction pressures were removed after aspiration. We interpreted the initial instability and the subsequent plastic deformation of the cell surface during aspiration in terms of a fracture between the cell plasma membrane and the cell body, which may involve destruction of part of the cortex. Models are presented that characterize the coupling strength between membrane and cell body by a surface energy sigma . We find sigma  approx  0.6(1.6) mJ/m2 at the leading (trailing) edge of wild-type cells.

Biophys J, August 2000, p. 707-719, Vol. 79, No. 2
© 2000 by the Biophysical Society   0006-3495/00/08/707/13  $2.00


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