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On shapes in living systems
Wednesday, May 4, 2011
During the initial months of preparations for the second edition of the Interdisciplinary PhD symposium, the symposium organizational team held a brainstorming session to reveal all the associations we have in our minds when we think of shapes. During this very lively discussion we made a mindmap that visually describes the topics we connected with shapes (see attached file below).
You can see our immediate thoughts were directed in describing different scales at which we can look at shapes in living systems - from the shapes of molecules, to the shapes of organelles and cells, extending to the shapes of organs and organisms and reaching the level of population structures.
We have considered how shapes evolve and what would be the benefits of different shapes. Evolution of shapes is tightly connected with the function of the shape, with examples of the emergence of bilateral and radial symmetry in animals and the very interesting phenomenon of mimicry, as well as fractal geometry found in mitochondria, capillary networks and other systems where the maximal surface contact is needed.
Shapes do change, and in the living system we can observe changes of shape during development of the organism, as well as a change in shape between different life stages (metamorphosis), all of which are induced and guided by the intricate influence of genes and environment. Change of shape is also observed on a molecular level, with enzymatic and receptor conformational changes, and also changes in the membrane, that allow the cell to perform complex regulation and physiology.
Yet another consideration to take into account when talking about shapes is the shape recognition. Even though today we mostly talk about this subject in terms of image analysis, recognition of shapes is important for individual cells and organisms. Cells can sense their environment, as well as sense and maintain their own shape. Last but not least, cognitive science explores how our brains recognize shapes, one of the first things we learn as babies.
To encourage speculative and creative thinking we also had in mind to discuss about the possible shapes that would arise on some other planet, with different physical, physiological and chemical constraints!
We would like to hear your associations and thoughts on shapes! Feel free to leave us a comment about the topic we have overseen and that you would like to draw attention to. We plan to have several brainstorming sessions during the symposium, but why not start even ahead and begin interacting using this blog!
Tamara Milosevic
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Thanks Celine for your contribution.
Very nice paper indeed.
The question that puzzles me over and over again every time I think about "shapes in living matter", is the following:
Is everything ruled (or could be easilly explained) by physics principles ?
As a (open-minded) biologist, I dare to say that the answer is No. Or the answer cannot be simply YES...
I mean, that what I find strange, amazing, beautiful, intriguing (etc) is the fact that the biological information (genes/code/signaling pathways/cooperation/cheating...) is completely in accordance with physics rules.
In other words, things look like if they are following pre-determined paths... Both during the development OR the maintenance of a shape !
Why ?
Am really wondering...
I like your mindmap on the topic§
For those who are interested in the physics that govern the emergence of different shapes, there is a good paper by V. Fleury and T. Watanabe entitled "ABOUT THE EQUILIBRIUM SHAPE OF FIBRED STRUCTURES AND BIOLOGICAL SHAPES".
The authors address especially the emergence of polarity in biological shapes (versus a perfect sphere) with an analogy with the formation of crystals.
to give you a taste, a piece of the abstract
(...)the fibred nature of biological tissue induces specific morphogenic properties. Fibred shapes can be calculated from physical principles borrowed from the theory of crystallogenesis. These give an intuitive insight into the shape of fruits or vegetables, buds and pins in botany, fingers, muscles, insects abdomen and heart in the animal realm, and also into other fibred structures such as the mitotic spindle. We predict the existence of bumps, apices or cusps at poles of fibred structures. An extrapolation to out-of-equilibrium growth predicts that these structures grow forward in the direction of the cusp, and that fibred organs should have a regular branching ordering.
pdf version can be found here: http://www.msc.univ-paris-diderot.fr/~vfleury/articles/fleurywatanabe1.pdf
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