Biology’s Birthday present for Alan Turing: Father of computer science and artificial intelligence, mathematician, cryptographer and…..biologist? 60 years after Turing published a hypothesis for pattern formation (such as zebra stripes) in biology, using math and simple diffusion, scientists have found evidence to support it. Like the yin and yang of Eastern philosophy, Turing proposed interactions between an activator (working over a short range) and an inhibitor (working over long range).
In a paper published in Nature Genetics, researchers discovered that two morphogens worked as an activator-inhibitor pair to develop striped ridges in the roof of a mouse’s mouth. Consider the reaction in Image 2 : A + B react to form C + D, where the product C feeds back autocatalytically to speed its production. C also activates an inhibitor, X*, which inhibits the reaction. Suppose these factors can regulate the genes that make skin pigment, then this interaction can give rise to the Turing patterns shown in the image.
To understand, look at Image 3: As the tissue expands,levels of the inhibitor diffusing from the stripes fall below a threshold (dashed line) so that the activator now gets back to work and produces a new stripe (dashed bar). The other panels show real data from the Nature Gen paper. Notice the appearance of the new stripe r3, first between r8 and r2 and then another (r4) between r8 and r3 both in the excised tissue and in the animal (in vivo). If diffusion of the inhibitor is blocked by making a cut next to the stripe, a new stripe emerges.
Image 4 shows the wonderful range of patterns that can be generated: A) Zebra stripes. B) Fish skin patterning. C) Phyllotaxis (leaf positioning). D) Developmental fields of leg segmentation in Drosophila. E) Cardiac arrhythmias (spiral/scroll waves).
What a neat 100 year birthday present for Alan Turing!
Sources: 1) Nature Genetics Abstract (image 3): http://www.nature.com/ng/journal/vaop/ncurrent/full/ng.1090.html
2) A good free read (images 2, 4): http://www.fasebj.org/content/17/1/1.full
3) Turing’s 1952 paper: http://www.dna.caltech.edu/courses/cs191/paperscs191/turing.pdf
Excerpt from Turing’s Abstract : “The purpose of this paper is to discuss a possible mechanism by which the genes of a zygote may determine the anatomical structure of the resulting organism. The theory does not make any new hypotheses; it merely suggests that certain well-known physical laws are sufficient to account for many of the facts.”