Tissue Patterning During Development

Abstract

Many patterns of cell and tissue organization are specified during development by gradients of morphogens, substances that assign different cell fates at different concentrations. Gradients form by morphogen transport from a localized site, but whether this occurs by simple diffusion or by more elaborate mechanisms is unclear. We attempt to resolve this controversy by analysis and computations of ligand-receptor models of the system. In addition we examine recent experimental data in ways that appropriately capture the complexity of the systems in which transport, receptor interaction, endo and exocytosis, and degradation occur together. We find that diffusive mechanisms of morphogen transport are much more plausible- and nondiffusive mechanisms much less plausible-than has generally been argued. At the end of the talk, I will discuss the applications of the ligand-receptor model to other tissue patterning problems.