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Abstract: Eukaryotic cells are large enough to detect signals and then orient to themby differentiating the signal strength across the length and breadth of thecell. Amoebae, fibroblasts, neutrophils and growth cones all behave in thisway. Little is known however about cell motion and searching behavior in theabsence of a signal. Is individual cell motion best characterized as a randomwalk? Do individual cells have a search strategy when they are beyond the rangeof the signal they would otherwise move toward? Here we ask if single,isolated, Dictyostelium and Polysphondylium amoebae bias their motion in theabsence of external cues. We placed single well-isolated Dictyostelium andPolysphondylium cells on a nutrient-free agar surface and followed them at 10sec intervals for ~10 hr, then analyzed their motion with respect to velocity,turning angle, persistence length, and persistence time, comparing the resultsto the expectation for a variety of different types of random motion. We findthat amoeboid behavior is well described by a special kind of random motion:Amoebae show a long persistence time ~10 min beyond which they start to losetheir direction; they move forward in a zig-zag manner; and they make turnsevery 1-2 min on average. They bias their motion by remembering the last turnand turning away from it. Interpreting the motion as consisting of runs andturns, the duration of a run and the amplitude of a turn are both found to beexponentially distributed. We show that this behavior greatly improves theirchances of finding a target relative to performing a random walk. We believethat other eukaryotic cells may employ a strategy similar to Dictyostelium whenseeking conditions or signal sources not yet within range of their detectionsystem.



Author: Liang Li, Simon F. Norrelykke, Edward C. Cox

Source: https://arxiv.org/







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