Superdiffusion of morphogens by receptor-mediated transport

Binding to cell surface receptors is thought to be essential for the transport of certain morphogens in developing tissues. The finite number of receptors per cell turns the tissue into a subdiffusive medium for the morphogens. We study a simple microscopic model of receptor-mediated transport and find superdiffusive spreading of morphogens. We propose that the superdiffusive spreading in a subdiffusive medium is due to a ratchet effect. A phenomenological model within the framework of the fractional Fokker-Planck equation allows us to analytically study the formation of morphogen gradients. Within this model, we show furthermore that the same features leading to the anomalous transport behavior also result in gradients that are robust against changes in the morphogen secretion rate. Together these findings show that anomalous transport in biological systems can be intimately linked to essential biological features.