Cell migration is driven by the establishment of disparity between the cortical properties of the softer front and the more rigid rear allowing front extension and actomyosin-based rear contraction. However, how the cortical actin meshwork in the rear is generated remains elusive. Here we identify the mDia1-like formin A (ForA) from Dictyostelium discoideum that generates a subset of filaments as the basis of a resilient cortical actin sheath in the rear. Mechanical resistance of this actin compartment is accomplished by actin crosslinkers and IQGAP-related proteins, and is mandatory to withstand the increased contractile forces in response to mechanical stress by impeding unproductive blebbing in the rear, allowing efficient cell migration in two-dimensional-confined environments. Consistently, ForA supresses the formation of lateral protrusions, rapidly relocalizes to new prospective ends in repolarizing cells and is required for cortical integrity. Finally, we show that ForA utilizes the phosphoinositide gradients in polarized cells for subcellular targeting.

Abstract:We study the influence of finite shear deformations on the microstructure and rheology of solutions of entangled semiflexible polymers theoretically and by numerical simulations and experiments with filamentous actin. Based on the tube model of semiflexible polymers, we predict that large finite shear deformations strongly affect the average tube width and curvature, thereby exciting considerable restoring stresses. In contrast, the associated shear alignment is moderate, with little impact on the average tube parameters, and thus expected to be long-lived and detectable after cessation of shear. Similarly, topologically preserved hairpin configurations are predicted to leave a long-lived fingerprint in the shape of the distributions of tube widths and curvatures. Our numerical and experimental data support the theory.

Laser tissue soldering (LTS) has variously interesting applications such as wound closure, anastomosis of blood vessels, and sealing corneal wounds. Since tissue properties such as optical absorption or thermal conductivity may differ, temperature control is essential to obtain full coagulation and to minimize thermal side effects. In this article, a non-invasive technique is proposed for temperature sensing by using CdSe-ZnS quantum dots (QDs) dissolved in protein solder, namely bovine serum albumin (BSA). The temperature measurement is conducted by monitoring the change in the photoluminescence spectra of the QDs. It is shown that the peak emission wavelength of about 653 nm of CdSe-ZnS QDs shifts linearly in a temperature range from 30 °C to 70 °C, with a coefficient of 0.153 nm °C -1 with increasing temperature. The wavelength shift can be determined by applying a small spectrometer with a CCD-array detector. The uncertainty associated with this method is estimated to be less than 6 °C in temperature. As the temperature increases, the measured signal strength initially remains constant and then falls off abruptly when exceeding 55 °C. The signal drop correlates with a phase change from a clear, low-scattering protein solution to strong-scattering solid material