Membrane Bending Modulus and Adhesion Energy of Wild-Type and Mutant Cells of Dictyostelium Lacking Talin or Cortexillins

Abstract

We have employed an interferometric technique for the local measurement of bending modulus, membrane tension, and adhesion energy of motile cells adhering to a substrate. Wild-type and mutant cells of Dictyostelium discoideum were incubated in a flow chamber. The flow-induced deformation of a cell near its adhesion area was determined by quantitative reflection interference contrast microscopy (RICM) and analyzed in terms of the elastic boundary conditions: equilibrium of tensions and bending moments at the contact line. This technique was employed to quantify changes caused by the lack of talin, a protein that couples the actin network to the plasma membrane, or by the lack of cortexillin I or II, two isoforms of the actin-bundling protein cortexillin. Cells lacking either cortexillin I or II exhibited reduced bending moduli of 95 and 160 k(B)T, respectively, as compared to 390 k(B)T, obtained for wild-type cells. No significant difference was found for the adhesion energies of wild-type and cortexillin mutant cells. In cells lacking talin, not only a strongly reduced bending modulus of 70 k(B)T, but also a low adhesion energy one-fourth of that in wild-type cells was measured.

Balance of actively generated contractile and resistive forces controls cytokinesis dynamics

“…1A). Each protein plays an important role in cytokinesis and cortical mechanics (7,(13)(14)(15)(16)(17)(18). Each mutant strain follows a unique time-dependent trajectory of furrow ingression.…”

Effective Membrane Model of the Immunological Synapse

“…Initially, the upper membrane was assigned a parabolic shape in the contact region, and the intermembrane distance was kept constant (∼ 50nm) outside the contact region. For the membrane parameters we use experimentally determined values [14] of γ = 700k B T /µm 2 and κ = 400k B T , and for the bond elasticity we take σ 1 = 13nm and σ 2 = 5nm [9]. Simulations were carried out for various ratios of C * 1 /C * 2 , and local concentrations of the TCR-MHCp and LFA1-ICAM1 were obtained from the intermembrane separation using Eqs.…”

Toward the Structure of Dynamic Membrane-Anchored Actin Networks

“…The static tether force, F t , needed to keep a membrane tether at a constant length, is approximated by F t = pB/R t + 2pR t T, where B is the bending modulus and T the effective membrane tension. 21 Although thin tethers have not been pulled out of the membrane of Dictyostelium cells, deflection of the membrane in response to shear forces has been measured in order to determine B and T. 22 Using the values of B = 2 pN x mm and T = 3 pN x mm -1 obtained by this method, and assuming their uniform distribution over the membrane, F t = 64 pN is calculated for filopodia with a radius of 100 nm. This is taken as a lower limit since much higher values for F t have been obtained by deforming Dictyostelium cells using micropipette aspiration.…”