Making waves: Pattern formation by a cell surface-associated signal
Angela Stevens and Lotte Sogaard-Andersen
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Submission date: 06. Apr. 2005
published in: Trends in microbiology, 13 (2005) 6, p. 249-252
DOI number (of the published article): 10.1016/j.tim.2005.04.002
Keywords and phrases: biological oscillations, pattern formation, negative feedback, mathematical modelling, intercellular signalling, chemosensory systems, myxococcus xanthus, gliding motility
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Starving Myxococcus xanthus cells organise into two strikingly different spatio-temporal patterns: rippling or aggregation of cells into fruiting bodies. Formation of both patterns depends on a cell surface-associated, non-diffusible signal, the C-signal. A key motility parameter modulated by the C-signal during pattern formation is the frequency at which cells reverse their gliding direction, with low and high levels of C-signalling causing an increase and a decrease in the reversal frequency, respectively. Recently, a simple yet elegant mathematical model was proposed to explain the mechanism underlying the non-linear dependence of the reversal frequency on C-signalling levels. The mathematical solution hinges on the introduction of a negative feedback loop into the biochemical circuit that regulates the reversal frequency. This system displays an oscillatory behaviour in which the oscillation frequency depends in a non-monotonic manner on the level of C-signalling. Thus, the biochemical oscillator recapitulates the effect of the C-signal on the reversal frequency. The challenge for biologists is now to test the mathematical model experimentally.