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Growing up to be a neurone

How do you turn one cell into another? Up to now, there were only two ways:

  • Embryonic stem cells
  • Induced-pluripotent stem cells

Stem cells are undifferentiated cells that are yet to be assigned a function within the body. They are naturally pluripotent. This means that they can form into any other cell in the body, from skil cell to neurone.

Embryonic stem cells

Embryonic stem cells, as their name suggests, come from embryos. Most embryonic stem cells come from embryos that have been fertilized in vitro (in a test tube). These are donated for research purposes with the consent of the donors. They are not produced from eggs fertilized inside a woman's body.

Induced pluripotent stem cells

Microscopic balls of cells

The embryos are in fact microscopic balls of cells four or five days old. Still, the practice is very controversial. Many people see it as killing a potential human being even though the cells couldn't survive without implantation. These ethical issues have meant that embryonic stem cells have always been in very short supply. There must be a better way, and there is!

Induced-pluripotent stem cells

Induced-pluripotent stem cells, usually called iPS cells, are made from ordinary non-pluripotent cells. Pluripotent is a word that is made from two others. Pluri means many, and potent means power. Both come from Latin. So pluripotent cells have many powers. In fact, just like an embryonic stem cell they hold the potential to become any kind of specialised cell. Induced-iPS cells seem like an ideal solution, but they do have one major drawback: they are very difficult to make.

Embryonic stem cells

How do you make an iPS cell?

The process would take pages to explain, too much for this article. You could always look it up! The core of the process is something called transfection: inserting specific stem cell associated genes into non-stem cells using viruses as a transfer tool. The cells that respond to these genes are then cultured and allowed to multiply. Easy! Well actually, very, very difficult.

The big breakthrough!

The big breakthrough that has just been achieved is to turn ordinary skin cells into nerve cells (neurones) without having to go through all the complex, difficult business of producing iPS cells first. We now think that ordinary cells contain much more information than we first thought. All cells know how to be all other kinds of cells. So a skin cell could become any type of cell in the body. The really key thing is that this process leaves out the stem cell stage completely.

Leaping over the stem cell stage

So, how it is possible to leave out the stem cell stage? What you have to be able to do is switch genes on. Imagine you want to build a super-cool sports car. The genes are like the blue prints you would use for the design of the car. Nature has drawn up these blueprints over millions of years of evolution. They contain all the engineering drawings, circuit diagrams and aerodynamic know-how to build a car. But, blue prints are just blue prints unless you have a workforce that can build the car properly.

The transcription factor

What researchers have managed to do is turn the plans into real pieces of cell. The process of gene expression is what it's all about. Here a gene which contains DNA is told how to make a copy of itself in RNA. This is called transcription. RNA can actually make things. If the transcribed RNA is messenger RNA or mRNA for short, it can manufacture a specific protein.

Cells are made of proteins. If you can persuade the right genes (DNA) to make copies of themselves as mRNA, they can make the bits to restructure the cell. Bingo, you have a workforce to turn your plans into a super-cool sports car. The persuasion that you need is a thing called a transcription factor; this is a protein, and it is this that instructs the gene to produce mRNA. Develop the right transcription factors and its all systems go!

This is what a team at Stanford University has succeeded in doing. The really astounding thing is that it requires only three transcription factors to change skin cells into fully functioning neurons that can make connections to, and communicate with, other neurons. What in effect you need is just three switches to turn on three genes and you can make a new type of cell. Astounding!

Why could this be so important?

This could represent the biological holy grail. It seems that it may be possible to turn one kind of tissue into any other kind of tissue you might need. This could be really useful in tackling all kinds of disease. It may be possible to produce a neurone therapy that would combat Althzeimers or Parkinson's. These are diseases that blight the lives of millions.

It's still very early days, many more transcription factors will need to be identified to produce precisely the right kind of neurone, but things look promising.

There will be many other applications. You could grow tissue in the lab to test new drugs or use for transplants. Just imagine being able to grow new tissue to repair a patient's heart. Of course, there would be no rejection problems because it would be the patient's own tissue that they would be receiving. Brilliant!

Will all these wonderful outcomes actually happen? No one knows yet. It does seem too good to be true, and it might be. There are always chances that turning on the genes may cause side effects like cancer-causing genetic mutations. But it just may work fine!

Fingers crossed!

The big questions:

What is a pluripotent cell?

What does RNA do?

What is mRNA?

What are embryonic stem cells?

What are iPS cells?