Signaling molecules called morphogens are thought to dictate tissue development by forming concentration gradients in the appropriate tissue. For example, dorsal-ventral patterning in the Drosophila embryo relies on gradients of activated morphogens of the bone morphogenetic protein (BMP) family. BMPs are produced dorsally, whereas their inhibitor, called Short gastrulation (Sog), is located ventrally. Eldar et al. formulated a general mathematical model of these molecules and additional known components of the signaling network that regulates this patterning event. The model revealed two underlying principles: restricted BMP diffusion and regulated Sog degradation. BMP diffusion increases when it is bound to Sog, and Sog is degraded when bound to BMP. Sog degradation allows the release of BMP and occurs at a distance from the ventral source of Sog. The authors validated these predictions experimentally in fly embryos and determined that these behaviors account for the system's resilience (robustness) to factors, such as varying gene dosage.
A. Eldar, R. Dorfman, D. Weiss, H. Ashe, B.-Z. Shilo, N. Barkai, Robustness of the BMP morphogen gradient in Drosophila embryonic patterning. Nature 419, 304-308 (2002). [Online Journal]