Physics for maggots

The development of a single cell into a fully functional organism is one of Nature’s most extraordinary phenomena. In the case of a fruit fly, the larva—a maggot—can walk away from the discarded egg shell just 24 hours after the egg is laid. Even more strikingly, if we measure the concentrations of fewer than a dozen crucial molecules we can see a “blueprint” for the segmented body plan of the maggot after just three hours, and this happens before cells start to move. These patterns are the result of information flow through a network of interacting genes, and the fly embryo provides a laboratory for studying the physics of this information flow. It turns out that development is extraordinarily precise and reproducible despite the fact that relevant molecules are at low concentrations and hence signals must be noisy. This motivates a physical principle: the relevant network is tuned to extract as much information as possible from a limited number of molecules. We’ll see how this theory can be connected to experiments, generating quantitative and parameter-free predictions.