Rearrangement of Spirals into Target Patterns in the Course of Dictyostelium discoideum Aggregation
published: Dec. 14, 2007, recorded: October 2007, views: 181
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The amoebae Dictyostelium discoideum has been frequently investigated as a suitable model system in the framework of biological pattern formation, signal transduction, cell differentiation and morgenesis (see  for a review). Under conditions of starvation populations of these amoebae aggregate due to chemical waves of cAMP. As a cAMP wave passes by a cell, it moves in the opposite direction, consequently towards the origin of the signal, as long as the cAMP-concentration is increasing over time. Formally this system my be regarded as a complex self-organizing network of cells, communicating through chemical medium. The spatio-temporal patterns of cAMP waves are a manifestation of the intrinsic properties of this active medium. Depending on the experimental conditions either spiral or circular-shaped waves of cAMP arise . Sometimes a pattern of one type is transformed into the other one in the course of time. In experiments two different examples for transitions from one to the other type of spatio-temporal patterns were reported . In the first case a continuous transition from the spiral type pattern to target waves was observed at the later stages of aggregation. In the second case the transition was induced by a spatially homogeneous cAMP pulse, when after resetting oscillating spots, bearing target patterns emerged instead of the originally present spirals. Similar results were reported by Lee et al. . The biological significance of different types of cAMP waves for Dictyostelium discoideum morphogenesis and the mechanisms of transitions between them are still unclear. Thus the question arises: what are the internal cellular properties and the external experimental conditions, which lead to such a transition? We attempt to find the answer to this question applying a mathematical modelling approach.
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