Learn the different types of stem cells for A-level biology. What the properties are and where these stem cells can be sourced. What are the pros and cons of using pluripotent stem cells in medicine and how might iPS cells be better.
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In this video I’m going to be going through the types of stem cells that you need to know for A-Level biology.
So just to recap then on what we mean by a stem cell and the A-level definition. So they are cells which are currently undifferentiated. They also have the ability to continually divide and then become specialized. So you would need to have both of those components in your definition. The fact that they can continually divide and they have the ability to become specialized in two types of cells.
And differentiation, which we’ve got here, the fact they’re undifferentiated cells; that is the process by which stem cells become specialized cells. And we have an example here in the image are the stem cell to showing you all the different types or some of the different types of specialized cells it could become.
So there’s different types of stem cells and that is referring to how many different specialized cells that particular type of stem cell is able to differentiate into.
So we’re going to go through those different types: totipotent, pluripotent, multipotent, and unipotent stem cells.
Totipotent Stem Cells
So begin with totipotent stem cells. And these are the stem cells that can divide into any type of cell in the body. So this is the type of stem cell that you would find in the very very early stages of an embryo. So they’re only available for a very limited time and as I said they can divide into or specialized differentiate into any type of body cell. And during development those totipotent cells translate only one part of the DNA, and that is how they eventually become specialized.
Pluripotent Stem Cells
Now in contrast pluripotent cells, these are the stem cells which we can see here in the inner mass of a blastocyst. And a blastocyst is about 3 to 5 days after fertilization that is what the embryo develops into. And the cells around the outside that we can see here in yellow; those will go on to make the placenta for the fetus and the blue cells in the middle are the pluripotent stem cells; and those are the cells that naturally would go on to make the fetus.
So if you take out one of those cells they’re pluripotent and they can divide into almost any type of cell. They just can’t divides or specialized to form placenta. So these are really useful for research. And at the moment they’re researching how you could use those types of cells and to treat human disorders. Because if those cells can differentiate into any type of stem cell, there’s the potential that they could be used to create damaged cells or tissues for example replace burnt skin cells or diabetics whose beta cells are not creating insulin (which is type 1 diabetes); potentially you could remove those and replace them with healthy beta cells created by pluripotent stem cells.
Or Parkinson’s disease where the neurons in the brain start to break down and they don’t produce enough dopamine anymore. So there’s a whole range of potential applications. Now I’m emphasizing potential because they’re not currently used in these treatments because in the research they have found issues and one of those issues is linked to the first part of the definition of stem cells; and that is the property that they have the ability to continually divide. And what they found when they’ve done this research in mice and other animals is that even when they have used stem cells to create new cells to replace damaged ones, unfortunately those cells continue to divide to create tumors.
Now the other issue is the ethics behind it. Because in order to get these pluripotent stem cells you have to create; if you want to use it to treat someone, you would have to create a zygote which is a clone of the patient you want to treat. And we call this therapeutic cloning because you are cloning that individual, but you never allow the embryo to go further than the early stages. So it’s not reproductive cloning where you’re cloning to make a living individual at the end. It’s therapeutic so you get the embryo or the blastocyst and then you just remove the stem cells you want.
So ethically two issues: therapeutic cloning but also destroying embryos which some people believe at that stage is already living. Some people believe there’s the potential for life there.
Multipotent and Unipotent Stem Cells
So multipotent and unipotent stem cells then. The multipotent ones have the ability to differentiate into a limited number of different cells. And you’d find these in the bone marrow, for example. And the stem cells, the adult stem cells found in bone marrow are multipotent because they’re able to differentiate into the different blood cells.
Now the final one unipotent; uni meaning one, they can only differentiate into the same type of cell. So skin cells can differentiate to make more skin cells or muscle cells will make more muscle cells.
So the sources of some of these stem cells then, I’ve gone through some of them as we went, but just in summary. Embryos up to 16 days after fertilization contain the pluripotent stem cells. So the blastocyst will be able to provide those stem cells for about day four or five up to 16.
Umbilical cord also contains some stem cells So sometimes people will keep the blood from the umbilical cord to have a source of multipotent stem cells along with the placenta that also has multipotent stem cells. And we said that the bone marrow is a source of multipotent stem cells as well.
So the last thing that you need to be aware of is, even more recent technologies of how to overcome the some of the issues that we discussed with the pluripotent stem cells. Because pluripotent would be the most useful in terms of applications in medicine. However there are pros and cons. Pros you could potentially treat many diseases. Cons are, and we’re just going to focus on here the ethical issues, of cloning and then destroying potential life, destroying the embryo.
Induced Pluripotent Stem Cells
And that’s why scientists came up with this idea of induced pluripotent stem cells, and often you’ll see that shorthand is IPS cells.
Now what these are, when you take a somatic cell (meaning a body cell) from an adult who’s giving consent. And that could just be a skin cell or the cheek cells so it’s easy accessible to get these body cells (somatic cells). And you can then manipulate the DNA inside of those cells by using appropriate transcription factors.
And transcription factors you learn about later and topic eight, these are molecules which can allow transcription to either occur or not occur for particular genes. And in that way if you turn on all the genes again in a cell, they are now no longer specialized cell and you’ve now induced to that body cell to become pluripotent again.
And that cell can then be used potentially for treatments. And in this way we’ve overcome the ethical issues of there’s no cloning involved and no embryos are destroyed.
And so how they do this, again I said a little bit about this, so the IPS cells are created from adult unipotent cells. Once you’ve then switched back on all the genes we call that return to the state of pluripotency. And that is using the transcriptional factors. So once you’ve done that, these induced pluripotent stem cells behave pretty much exactly the same as the pluripotent cells from a blastocyst.
They have also shown self new properties and they can divide indefinitely to give limitless supplies. So you wouldn’t have to go through this whole process every time. You can allow them to divide and then you can keep the source of them for that particular patient. So that’s it for our stem cells types and applications [Music]