Are there different types of stem cells?

Apologies for taking so long to write this next blog post. Things have been busy in the lab for me the last few months, but now I’m back to writing my blog and hopefully teaching those who are interested something new on this gloomy, rainy Thursday 😦

So, in my last blog post I introduced the unique characteristics of stem cells. As a quick recap as it was such a long time ago now:

  • they are capable of dividing and renewing themselves for long periods of time; called self-renewal
  • they are unspecialised cells; so have a degree of potency which I will go into more a bit later
  • and they can give rise to specialised cells types in a process called differentiation

Although all stem cells have these characteristics, there are different types of stem cells. Today I’m going to talk about embryonic and adult stem cells and then in the next blog I’ll introduce you to induced pluripotent stem cells.

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So, just as a bit of a side note, I want to address this idea of potency that I mentioned before.

Cell potency is a cell’s ability to differentiate into other cell types and so stem cells are characterised by this property. So, we have four different potencies ranging from being able to differentiate into the highest number of different cell types to the least. They are totipotent, pluripotent, multipotent and unipotent.

Totipotent cells essentially equate to the fertilised egg. They can differentiate into all cell types of the body and also the cells that will give rise to the placenta (extra-embryonic tissues). Pluripotent cells are the next step down, where these can differentiate into all cell types of the body, but not the extra-embryonic tissues. Next, comes multipotent stem cells. These cells can become multiple cell types, but only those within one tissue type, so are more restricted than pluripotent cells. Finally, unipotent cells will only make one cells type depending on which tissue they come from. So, if they come from the heart they will only make heart cells etc..

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So, back to the different types of stem cells that we will discuss today; embryonic and adult.

As the name suggests, embryonic stem cells come from embryos and with that comes many ethical issues. Most of these cells come from embryos that have been fertilised in vitro in IVF clinics and then donated for research purposes with informed consent of the donors. They DO NOT come from eggs fertilised inside a woman’s body! Embryonic stem cells are pluripotent cells and can remain undifferentiated in culture for long periods of time. However, scientists often check these cells to see if they undifferentiated by looking at what proteins/markers these cells produce. Three of the most important proteins/markers that embryonic stem cells produce are called Oct4, Nanog and Sox2. As they are linked with characterising embryonic stem cells, which are pluripotent cells, these proteins are often referred to as pluripotency markers. They help turn genes on and off at the right time during important processes like differentiation and embryonic development.

So, as long as embryonic stem cells express these pluripotency markers they will remain undifferentiated.

Some of my work is looking at what proteins might stop these cells producing these pluripotency markers, but that’s for another time 🙂

Moving onto adult stem cells, what are they?

An adult stem cell is thought to be an undifferentiated cell, found among differentiated cells in a tissue or organ. Adult stem cells are multipotent and so their main role is to repair and maintain the tissues where they are found.

When taken out of the body, these cells lose their ability to continuously divide, so generating larger quantities is difficult. Scientists in many laboratories are trying to find better ways to grow large quantities of adult stem cells in cell culture and to manipulate them to generate specific cell types so they can be used to treat injury or disease. Some examples of potential treatments include regenerating bone using cells derived from bone marrow stroma, developing insulin-producing cells for type 1 diabetes, and repairing damaged heart muscle following a heart attack with cardiac muscle cells.

Research on adult stem cells has generated a great deal of excitement. Scientists have found adult stem cells in many more tissues than they once thought possible. This finding has led researchers and clinicians to ask whether adult stem cells could be used for transplants. In fact, adult hematopoietic, or blood-forming, stem cells from bone marrow have been used in transplants for more than 40 years. Scientists now have evidence that stem cells exist in the brain and the heart, two locations where adult stem cells were not at first expected to reside. If the differentiation of adult stem cells can be controlled in the laboratory, these cells may become the basis of transplantation-based therapies.

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