Stem cells are unique because they have three distinct properties:
- They can divide and renew (proliferate) themselves over long periods of time
- They are not specialised (unlike every other cell in the body)
- They can give rise to these others specialised cells (differentiate)
Proliferating stem cells that have been allowed to divide and renew for many months in a lab can potentially create millions of new cells, and if those newly created cells remain unspecialised, they can in turn go on to proliferate for the long term.
However, saying that, embryonic stem cells differ from adult stem cells in that embryonic stem cells can proliferate for over a year in the right lab conditions, whereas adult stem cells can’t.
Recent research looking into the effects of Royal Jelly on stem cells could provide the answer to prolonging the life of adult stem cells without them differentiating, given its rejuvenation properties, but how does time affect embryonic stem cells?
Understanding the difference between why embryonic stem cells can continue to proliferate without causing undue harm to the body whereas the proliferation of adult stem cells can lead to abnormal cell division which can result in cancer, could enable scientists to grow both embryonic and adult stem cells more efficiently under lab conditions.
The differentiation of stem cells
What causes stem cells to differentiate continues to fascinate scientists because it has taken them years of trial and error to prevent stem cells from spontaneously differentiating in the lab into different types of cells.
One of the special properties of stem cells is that they are unspecialised, meaning they do not possess any tissue specific structures that require them to perform tissue specific functions. However, the purpose of stem cells is to be able to become any of these specialised cells – heart cells, muscle cells, blood cells, should they be required.
And when a stem cell undergoes its transformation from unspecialised to specialised, the process is known as differentiation.
The process of differentiation
There are several steps that stem cells go through during differentiation, becoming ever more specialised the further along the process they go. The stem cell’s differentiation is triggered by internal and external signals that control each step. Internal signals are created by the stem cell’s own genes, external signals come via chemicals excreted by surrounding specialised cells, physical contact with these specialised cells or even certain molecules in the stem cell’s environment.
Questions still remain however about whether the process of differentiation is the same for all stem cells, whether they all react to the same internal or external signals, or whether specific signals trigger differentiation into the specific specialised cell types.
By addressing these questions surrounding differentiation, scientists will be able to better control lab grown stem cells in order to help develop stem cell based therapies, or experiment with new drugs.
One of the factors that scientists need to address is the issue of time and how it affects stem cells.
How time affects stem cells
In a recent study published in Molecular Systems Biology, researchers from the lab at David Suter, EPFL, found that changes in time affected what type of specialised cell the embryonic stem cells they were studying would become. More specifically, they looked at two transcription factors – SOX2 and OCT4, both of whose levels changed in the embryonic stem cell over time, given that both of these factors are important for the differentiation of embryonic stem cells into specialised cell types.
Their study revealed that small changes in the levels of either SOX2 or OCT4 resulted in altering the fate of the embryonic stem cells, but only during the initial cell growth phase.
What does this mean?
More research into the effect of time on stem cells is required, but knowing that the fate of the embryonic stem cells can change over time, could mean placing a limit on scientists’ ability to alter a cell’s fate for stem cell therapy.
But that isn’t necessarily a bad thing, because if these fluctuations are true, scientists can research how to suppress the changes, allowing them better control over the ultimate fate of the embryonic stem cells.