Developmental Biology

Turing in Real Life

Science Signaling  15 May 2012:
Vol. 5, Issue 224, pp. ec138
DOI: 10.1126/scisignal.2003218

Turing proposed a reaction-diffusion model composed of a long-range inhibitor and a short-range activator, which drives production of itself and the inhibitor, to account for the formation of complex patterns in nature. Although Turing’s model produces patterns similar to those found in biological systems, and although inhibitors and activators with differences in range are found in biology, it is unclear how the required differences in activator and inhibitor ranges are generated in vivo. Difference in ranges could be due either to differences in diffusivity or rate of clearance of the two signals. Müller et al. examined this question in the context of Nodal and Lefty signaling during zebrafish embryogenesis. The Nodal proteins Cyclops and Squint act as short-range activators, and Lefty1 and Lefty2 are long-range inhibitors. Nodal signals enhance their own production and production of Lefty1 and Lefty2. The authors measured distributions of fluorescent Nodal and Lefty proteins in blastula-stage embryos using microscopy. The results of pulse-labeling assays showed that the half-lives of Nodal and Lefty proteins were very similar, despite large differences in range. Fluorescence recovery assays enabled analysis of the mobility of the proteins on a faster time scale than the half-life of the proteins and showed that the diffusion coefficients of Lefty proteins were much larger than those of Nodal proteins, reflecting the differences in their ranges. Thus, for Nodal and Lefty, diffusivity plays a primary role in governing signal range and serves as the biophysical basis for pattern formation during this stage of embryogenesis. The measured biophysical properties of Nodal and Lefty proteins also provide experimental support for Turing’s reaction-diffusion model of morphogenesis.

P. Müller, K. W. Rogers, B. M. Jordan, J. S. Lee, D. Robson, S. Ramanathan, A. F. Schier, Differential diffusivity of Nodal and Lefty underlies a reaction-diffusion patterning system. Science 336, 721–724 (2012). [Abstract] [Full Text]