Amanda, Facebook asked:
How are stem cell fates controlled?
Richard Adams - The stem cells at the very beginning of development do indeed know all of the information that they need to make any tissue of the body, but driving them towards making any particular tissue can be done in a number of ways. You can either expose them to particular growth factors - diffusable signals that come from one cell to signal another cell to cause them to make a particular cell type. And you can also influence them by their physical environment, if you grow them on substrates that are stiffer or more flexible then it changes the kinds of cells that grow in culture.
Simon - Now Neil, you're looking at a later stage of development, are these the same cues that are taking place, or are there extra signals such as hormones that are involved in activing genes?
Neil Vargesson - In limb development, stem cells have already done their job by that point, and you have a heterogeneous population of cells, lots and lots of different cell types coming in with lots of different signals, and they all are signalling towards one another, setting up signalling cascades. Sitting at the top of that, the hox genes, for example, and you'd also have signals such as sonic hedgehog and fibroblast growth factors all talking to one another, and it's that combination of how that cascade is controlled, and how they signal to each other and control each other that we're looking into right now. One of the big questions in developmental biology is how this how these networks are controlled.