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Day 4: Multi-level modelling in morphogenesis

The fourth day of the multi-level modelling in morphogenesis course was started by Dr Stan Maree giving a talk outlining how modelling has helped us understand the life-cycle of cellular slime mold.

Under normal conditions cellular slime molds act as individual cells feeding on bacterial. However, during starvation hundred of thousands of these cells come together to form a slug like creature that can migrate across a surface guided by, amongst other, thermotaxis. Finally the slug culminates by transforming itself into a fruiting body consisting of a spore head on a small, tapering stalk.

Dr Maree then illustrated, though modelling, that all of the aspects of the life-cycle unfold by combining only a few processes. The main processes being:

  • excitable media through cAMP
  • chemotaxis towards cAMP
  • differential cell adhesion
  • cell differentiation

The fact that this parsimonious description can account for the complex behaviour of development is mainly due to the fact that one can get differing behaviours by operating on different levels, e.g. individual cells versus clusters of cells versus a slug of cells. For example pressure waves emerge and guide the culmination stage solely due to cell adhesion and excitable media. While adhesion is a property linked to cell membranes which ensures that cells adopt different shapes and that clusters of cells also develop certain topologies. At the highest level the Dictyostelium slug can even act as a lens and use this effect to be able navigate up light gradients, which could be understood through modelling. This combination of modelling at many different scales is a core aspect of this course.

The participants were then invited to work though workshop material on aggregation and cAMP waves, aggregation and slug formation, thermotaxis and culmination.

In the afternoon there was a keynote lecture by Dominique Bergmann.

Dr Bergmann’s group is interested in the the development of stomata, in particular the spatial organization of the stomatal lineage. Dr Bermann’s group is largely experimental. However she is very keen to interact with modellers and it was great to see her inviting the participants of the course to tackle questions that her group are currently battling with. Questions which could potentially be answered by modelling.

Dr Bergmann talk gave fascinating insight into the mechanisms by which stomata are patterned across leaves, starting from the simple rule that no stomata may touch each other. The talk revealed that flexible patterned development can arise by regulating the expression of key transcription factors through positive an negative feedback loops. Furthermore by studing the differences between the regulatory networks in grass and Arabidopsis Dr Bermann managed to refine important features of the mechanism of patterning, highlighting the value of studying different organisms.