Manipulating a morphogen in space and time

This proposal addresses the fundamental ‘rules of life’ remit of the BBSRC, specifically: How our body is formed and what happens if this process goes awry? Embryonic development starts from a fertilised egg and will ultimately result in the formation of the adult anatomy. Obviously, this entails an increase in cell number, but an essential feature of this process is that it involves making group of cells different from each other, in space and time, so they do different things. This is underpinned by stereotypical use of instructive signals, and alterations to the usual sequence of events can lead to different outcomes. A morphogen is a special class of signalling molecule that acts during embryonic development to generate a variety of cell states. In response to distinct threshold levels of morphogen signalling, cells follow different fates and form different structures. Therefore, within a given territory, a single morphogen can generate multiple outcomes. While the significance of morphogen activity is widely appreciated, we still do not have a clear understanding of how morphogens work and, more specifically, how their activity can be modulated during embryonic development to modify the shape and form of the anatomical structures they generate. This is an issue, both within a species, in the formation of different structures, and during evolution, in the generation of morphological diversity across different species. Disruption of normal morphogen activity is also associated with congenital birth defects and can be responsible for structures not forming or additional elements being present, such as supernumerary (additional) digits in the hand. Our aim is to study the parameters of morphogen action by modulating physiological morphogen signalling levels in space and time and to understand the consequences of these manipulations for the allocation of different cells states/fate and the later morphology of the limbs. This is important as morphogens act in both a concentration and time dependent manner. Cells respond differently to a morphogen depending on the concentration of the signalling molecule they have been exposed to and the length of exposure. We will create experimental situations in which cells of the limb bud are exposed to low, intermediate, or high physiological levels of the morphogen, SHH, and modulate the length of time cells are exposed to these levels of signalling. This study will advance understanding of how a single type of signalling molecule can generate different anatomical structures and how this property can be employed within a developing organism to generate features such as the different digits of the hand and feet. This study will also fruther develop an experimental methodology in the chick model organism that will contribute to the objectives of the NC3Rs.