Physical Society Colloquium

Spatio-temporal pattern formation in embryos:
How diffusion can help create order

Cécile Fradin

Department of Physics and Astronomy
McMaster University

Due to the landmark works of, amongst others, Einstein and Perrin, molecular diffusion in simple fluids has long been a very well understood process, whose study has played a major role in the development of statistical physics. In the context of inert physical systems, diffusion is regarded as a process that evens out concentration and increases entropy. However, in the context of the living cell, where diffusion is a ubiquitous process, it is quite striking that it can both be much more complex than in simple fluids and that it can coexist with a very tightly orchestrated multi-scale order. A particularly interesting case is that of the spatio-temporal pattern formed by molecules called morphogens, because it provides a striking example of how order - the morphogen concentration gradient - can be established in biological systems in spite of a noisy background process - diffusion. Morphogens form concentration gradients across early embryos and effectively provide a postal code that let cells know where they are located within the organism, allowing them to then differentiate according to their position. For this process to be reliable, both the establishment and the readout of the gradient must be precise and robust. In this seminar, I will make the case that diffusion plays an essential role in both the establishment and maintenance of morphogen gradients, an idea which has long been the object of controversy.