How does a complex organism, like a person, develop from a single cell? Stem cell research is providing the answer to this question and many more.

What are stem cells?

Stem cells are cells that have not differentiated. They are unique because they can divide and grow for a long period of time without becoming a particular type of cell.

Why are stem cells important?

Stem cells have the ability to become any of the 200 cell types found in our bodies. For example, when given a particular signal, a stem cell can become a beating heart cell or, with a different signal, can become an insulin producing pancreas cell. Because of this amazing ability, scientists are hoping to use stem cells to replace cells that are lost or damaged from disease or injury.

Types of stem cell

Scientists are using two different types of stem cells in their research:

  • Embryonic stem cells
  • Adult stem cells.

Embryonic stem cells give rise to all cell types that are needed to make a living organism. An embryo begins as a single, fertilised egg that divides to form a blastocyst. The blastocyst is made up of embryonic stem cells, which can differentiate into all cells, such as brain, heart, liver, and lung cells.

Embryonic stem cells can be collected from unused fertilised eggs from in vitro fertilisation (IVF). If stem cells are harvested, the embryo will not develop into an adult, which presents considerable ethical issues.

Adult stem cells are found in small numbers in adult organisms, particularly in tissues like brain, bone marrow, muscle, skin, and liver. Adult stem cells replace cells lost through normal wear and tear, damage, or disease. For example, red blood cells only live for 120 days and are constantly being replaced by new blood cells derived from adult stem cells in the bone marrow. Adult stem cells can be extracted from adult tissues, although this can be difficult to do in the lab.

How are embryonic and adult stem cells different?

Embryonic and adult stem cells differ in the number and type of cells they can become. Embryonic stem cells are pluripotent, which means they can become any cell type in the body, whereas adult stem cells are multipotent, which means that they can normally only become cells of the same type as the tissue they came from. The ability of a cell to differentiate into different cell types is known as plasticity.

Embryonic stem cells appear to be immortal and can be grown in the lab indefinitely, whereas adult stem cells are difficult to grow in the lab and tend to die off like typical tissue cells. Also, adult stem cells are much harder to find, as they are only present in small numbers in adult tissue.

When did stem cell research begin?

The last 10 years have seen a huge increase in research into stem cells, but when did it all begin? Find out more in this this timeline of stem cell research.

The idea that stem cells existed in the brain was controversial for many years, find out more about how our ideas were changed in the article, Stem cell therapy – a bird-brain idea?

Stem cell therapy

Transplants of stem cells from bone marrow were first done in the early 1970s and are now regularly used to treat leukaemia. Scientists are currently researching whether stem cells can be used to treat other diseases, like Parkinson’s disease, type I diabetes, and heart disease.

Find out more about the history of bone marrow transplantation in this timeline.

Ethics of stem cell therapy

The use of stem cells from embryos for therapeutic cloning is controversial. In New Zealand, strict regulations govern research into stem cell therapies.

    Published 15 November 2007