05.02 Structure Does Not Determine Function – Beyond Networks: The Evolution of Living Systems
Channel: Johannes Jaeger
Date: 2020-05-05

Module 5 of "Beyond Networks" gets into the nitty-gritty of the course, covering network analysis and mechanistic explanations. In this second lecture, we get to the core message of the course: structure does not determine function. I introduce the divide-and-conquer method of subdividing complex networks into subcircuits or motifs, which are simple enough to understand what they do. Unfortunately, even the simplest network motifs exhibit behaviour that is dependent on both their context within the larger network and the strength and nature of the interactions involved. Even the simplest network motifs can exhibit a considerable range of qualitatively different types of behaviour. I illustrate this using the example of my favourite small network: the AC/DC circuit. 

Network motifs are hard to miss these days. But if you don't know where to start, read Uri Alon's 2007 review in Nature Reviews Genetics (Vol. 8: p. 450). 

Eric Davidson and Doug Erwin describe their take on subcircuits (and their importance for evolution, more on that later...) in their 2006 Science paper (Vol. 311: p. 796). I find it a beautiful paper, because it makes their thinking extremely explicit. All the more easy to disagree with it! 

The repressilator circuit was first described in Elowitz & Leibler (2000; Nature, Vol. 403: p. 335), a pioneering piece of work in synthetic biology. The AC/DC circuit was first described by James Briscoe's group in Panovska-Griffiths et al. (2012) in Journal of the Royal Society Interface (Vol. 10, 20120826). Our own analysis of these circuits can be found in Verd et al. (2019; eLIFE, Vol. 8: e42832).

I'll have a lot more to say about how structure does *not* determine function in lecture 05.04.