Cell Differentiation (Specialization)
Cell differentiation is the process where cells acquire a new identity. This allows the cell to perform more specialized roles in the body. Almost all cells in the body differentiate from stem cells. As you go about your day, take a moment and consider all the jobs your cells are doing. Your neurons in your brain are responsible for your thoughts and feelings. Heart cells pump blood throughout your body. Your skin cells defend your body from invaders.
It takes a lot of work to keep you healthy! But where did all these cell types come from? How does a cell figure out what job it needs to do? It all starts with stem cells.
A stem cell is a cell that can renew itself. This means that when the stem cell replicates, its “daughter cell” is identical to the parent cell. A stem cell must also be able to generate a more differentiated (specialized) cell. How does a stem cell know whether to produce another stem cell or a more differentiated cell? A stem cell receives its instructions from the environment around it. The home where a stem cell lives is the stem cell “niche”. Signals from the niche will inform the stem cell what sort of cell the organ needs the most!
This diagram shows the decisions a stem cell may make.
In the diagram above, purple are the stem cells. They may make more stem cells, or decide to make a more differentiated cell (in blue). These differentiated cells can go on to become more specialized (yellow cells).
Where are Stem Cells Found?
Stem cells are present in nearly every organ in our body. When our organs need new cells, stem cells divide and replenish the organ with fresh cells. For example, when neural stem cells divide, they make a choice. They can make more stem cells, or they can create more differentiated cells like neurons. In the bone marrow, stem cells create differentiated cells you need to make blood.
Genes and Flexibility
Every cell that you look at has the same DNA. What makes cells different from one another is which genes are turned on in the DNA. A liver cell, for example, will only turn on liver genes. A skin cell will only turn on skin genes, and so on!
Very early stem cells have a lot of flexibility in what genes they turn on and off. As they differentiate, they become more selective in what genes are on. For example, a neural stem cell will turn off the genes for many other cell types. This leaves only the “neural” genes activated. The more differentiated a cell is, the more specialized its set of “active” genes will be.
If stem cells can produce differentiated cells that our bodies need, why don’t we live forever? Why do we age? These topics are under intense investigation in the lab.
Aging results in many changes to our body.
Scientists theorize that as time goes on, our stem cells become damaged. When enough damage occurs to these stem cells, they are no longer able to sustain themselves. If our stem cells are exhausted, then no differentiated cells can come from them!
This is bad news for organs. A lack of stem cells means that there are no more healthy cells to replace damaged ones. Over time, this will cause an organ to stop functioning.