Social Amoeba Calculate To Communicate

Slime mold can ‘calculate’ the fold-change of signaling molecules, an ability that helps it behave like a multicellular organism.

AsianScientist (Aug. 14, 2017) – Rather than relying on the absolute change in the levels of signaling molecules, the soil-dwelling social amoeba Dictyostelium responds to fold-change of cell-to-cell communication molecules. These findings, published in the Proceedings of the National Academy of Science, could be applied to other scenarios where intercellular communication is important, such as infection, immunity and embryonic development.

Cell-to-cell signaling plays a pivotal role in cellular and tissue organization. A solid communications medium analogous to phone cables seems ideal for establishing the smooth transmission of information between cells. However, as cells most often use freely diffusing molecules in extracellular fluid for communications, the molecules’ concentration varies greatly according to changes in the environment like cell densities and the presence of diluting or degrading factors.

In some organisms, cellular communications are established even under fluctuating conditions, a phenomenon scientists called robustness. Although it robustness is one of distinct features that separates living systems from non-living materials and artificial machines, mechanisms to achieve robustness remain poorly understood.

In the present study, a research group led by Associate Professor Satoshi Sawai at the University of Tokyo set out to find out how Dictyostelium— an organism known as a social amoeba that shows conditional multicellularity—can communicate with each other even under conditions of varying cell density.

Through quantitative live-cell imaging with a fluorescence microscope of single cell-level response to signaling molecules, the research group revealed that the Dictyostelium cells’ response remains identical under various background concentrations of stimulus as long as the fold change is the same. In other words, a change in the stimulation level from one to two produces the same result as that from two to four, both representing a twofold change, although the change difference varies.

Mathematical analysis shows that this fold-change dependence ensures population-level cooperative phenomena to exhibit the same dynamics regardless of cell density. Since similar fold-change detection is well known in human sensory systems, the present results suggest a universal feature of signal processing across many levels of the biological hierarchy.

“I was blessed to have met talented graduate students Keita Kamino and Yohei Kondo, co-authors of the current study, who were interested in applying their mathematical and physical science talent to biological problems. It looked rather complicated at first, involving tens of thousands of cells that collectively create unpredictable patterns in space and time, but what it boiled down to was a rather simple mathematical principle that underpins the robustness,” said Sawai.

“This is one of the rare examples in which this kind of simple mathematical principle was demonstrated in biology. We hope that the finding will inspire and stimulate studies in other biological systems and deepen our knowledge of universality in biological phenomena.”

The article can be found at: Kamino et al. (2017) Fold-change Detection and Scale Invariance of Cell-Cell Signaling in Social Amoeba.


Source: University of Tokyo; Photo: Pixabay.
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