Sorry to take so long to post this piece. I’ve been spreading myself too thin, lately, and as a result I’ve chipped away at many problems, but demolished none. Nonetheless, after some selective reprioritization, I’ve found the time to tell you about this curiosity of a paper.
Nykter, M., Price, N.D., Aldana, M., Ramsey, S.A., Kauffman, S.A., Hood, L.E., Yli-Harja, O., Shmulevich, I. (2008). Gene expression dynamics in the macrophage exhibit criticality. Proceedings of the National Academy of Sciences, 105(6), 1897-1900. DOI: 10.1073/pnas.0711525105
Please don't hate me for covering a paper from the Proceedings of the National Acadamy of Sciences (PNAS). They may have deeply dubious refereeing practices, but they remain a prestigous publisher and somehow their impact factor continues to hover over the heads of most other journals.
This paper is a bit of a shark. It looks quite innocuous on the surface, but beneath the surface lurks a neat portent, a harbinger of the shape of things to come and that's why I've chosen to blog about it.
The authors argue that the networks of interacting genes, proteins, rnas and biomolecules that mediate signalling within and between macrophage cells is critically poised, sitting happily on the boundary between ordered and disordered phases. Such systems are well studied within physics and their behaviour has formed the field of critical phenomena. The authors argue that critical systems conserve information over a time course and so by testing whether the networks conserve information, we can infer whether they are critical. If this were convincingly shown, it would be a real first and would have implications for many cell types. It would probably also get them a Nobel prize. But it's really not clear whether we can turn this relationship on its head and say that if critical systems conserve information, information conserving systems must be critical. For example, the level of information in random noise would also be conserved even though it would be zero. No doubt the PNAS' toothless refereeing practices haven't helped here.
But, for all its faults, this paper does show something very important. Vision. Whether signalling networks are critical or not, these are exactly the questions we want to be able to answer. And, hopefully, one day, we will. Hopefully, one day, we will have the deep understanding that condensed matter physicists routinely enjoy. But to get there we'll need the enthusiasm of authors such as these, even if they do occasionally get carried away.