Question: How do stem cells make choices?

David Grainger answered on 15 Jun 2018:

Great question. This is a very broad topic that thousands of scientists work on in many different contexts. A stem cell normally sits at a decision point where given message 1 it will become cell type A (e.g. a heart cell) but given message 2 it will become cell type B (e.g. blood cell). There are two sides to how a stem cell makes choices.
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Firstly, is what causes it to change and make a choice? In order to remain a stem cell, often the cell must receive messages from the other cells in it’s environment to keep its stem cell properties. So one way to make a stem cell make a choice is to take these messages away. Alternatively, a stem cell could recieve a new message from it’s surroundings that will cause it to make a choice. When we grow stem cells in test tubes, we mimic what happens in the body by adding or removing messages, just like in an animal’s body. Since the environment of a stem cell is very complex, it receives many signals and the combination of these determines which choice the stem cell will make.
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The other question to ask is how these different messages cause the stem cell to change. Once a stem cell has made a choice it will look and behave differently despite having exactly the same DNA in it. Really what gives a cell it’s identity is not the DNA within it (though this is important) but rather which bits of the DNA are on and off. We can separate the DNA into functional units called genes. Each gene has a different function within the cell so by turning on or off different genes you change how the cell responds to different messages. So when a stem cell receives a message from it’s environment, this will be read by the cell and cause a change in which genes are on and off. How genes are turned on and off is a whole other field of it’s own but there are many ways it can happen.