TY  - JOUR
A1  - Westendorf, Christian
A1  - Negrete, Jose
A1  - Bae, Albert J.
A1  - Sandmann, Rabea
A1  - Bodenschatz, Eberhard
A1  - Beta, Carsten
T1  - Actin cytoskeleton of chemotactic amoebae operates close to the onset of oscillations
JF  - Proceedings of the National Academy of Sciences of the United States of America
N2  - The rapid reorganization of the actin cytoskeleton in response to external stimuli is an essential property of many motile eukaryotic cells. Here, we report evidence that the actin machinery of chemotactic Dictyostelium cells operates close to an oscillatory instability. When averaging the actin response of many cells to a short pulse of the chemoattractant cAMP, we observed a transient accumulation of cortical actin reminiscent of a damped oscillation. At the single-cell level, however, the response dynamics ranged from short, strongly damped responses to slowly decaying, weakly damped oscillations. Furthermore, in a small subpopulation, we observed self-sustained oscillations in the cortical F-actin concentration. To substantiate that an oscillatory mechanism governs the actin dynamics in these cells, we systematically exposed a large number of cells to periodic pulse trains of different frequencies. Our results indicate a resonance peak at a stimulation period of around 20 s. We propose a delayed feedback model that explains our experimental findings based on a time-delay in the regulatory network of the actin system. To test the model, we performed stimulation experiments with cells that express GFP-tagged fusion proteins of Coronin and actin-interacting protein 1, as well as knockout mutants that lack Coronin and actin-interacting protein 1. These actin-binding proteins enhance the disassembly of actin filaments and thus allow us to estimate the delay time in the regulatory feedback loop. Based on this independent estimate, our model predicts an intrinsic period of 20 s, which agrees with the resonance observed in our periodic stimulation experiments.
KW  - Dictyostelium discoideum
KW  - microfluidics
KW  - caged cAMP
KW  - delay-differential equation
Y1  - 2013
U6  - https://doi.org/10.1073/pnas.1216629110
SN  - 0027-8424
VL  - 110
IS  - 10
SP  - 3853
EP  - 3858
PB  - National Acad. of Sciences
CY  - Washington
ER  - 
TY  - JOUR
A1  - Hasinovic, Hida
A1  - Friberg, Stieg E.
A1  - Kovach, Ildyko
A1  - Koetz, Joachim
T1  - Janus emulsion drops - equilibrium calculations
JF  - Journal of dispersion science and technology
N2  - Experimental results indicated the contact angles in the drops of Janus emulsions formed in a one-step mixing process to be invariant within a significant range the oil volume ratios, similar to the results from microfluidics emulsification. Since this result points to a connection between the kinetically formed emulsions and the local equilibrium topology of emulsion drops, the effect of interfacial tensions on the morphology of Janus emulsions was estimated from the equilibrium interfacial tensions at the line of contact. Realistic values of the tensions revealed the limited range of these to obtain Janus drops and also offered correlation between the equilibrium entities and the curvature of the interface between the two oils.
KW  - Drop morphology
KW  - equilibrium topology
KW  - Janus emulsions
KW  - microfluidics
KW  - multiple emulsion preparation
Y1  - 2013
U6  - https://doi.org/10.1080/01932691.2013.763728
SN  - 0193-2691
SN  - 1532-2351
VL  - 34
IS  - 12
SP  - 1683
EP  - 1689
PB  - Taylor & Francis Group
CY  - Philadelphia
ER  -