As an embryo grows it has to be able to produce a wide range of cell types, from brain and skin cells to liver and kidney cells. It achieves this by producing a kind of "starter" cell that has the potential to grow into any of the 210 cell types found in the body, the so-called stem cells.
Researchers are interested in stem cells because of their potential to become any type of cell. This raises the possibility that they could be used to reverse degenerative diseases such as Parkinson's or to reconnect severed nerve tissues.
Stem cells can be recovered from a variety of sources, including embryos, adult organs and tissues and also from the placenta and umbilical-cord blood.
Embryos produce large numbers of stem cells making them an attractive source for these cells. The embryonic cells also appear to be the most "plastic" or plenipotent of all stem-cell types, making them of particular interest to researchers.
Adults also produce stem cells in a range of tissues, including bone marrow and the liver. These cells are far less plastic, however, and only tend to become the type of adult cells in the places where they are found. For example, stem cells from the liver tend to become liver cells.
Placental and umbilical cord stem cells are easily recovered but behave more like adult than embryonic cells, making them less attractive for research.
The EU Commission wants to use EU funds for research into embryonic stem cells. The funds would be used to study surplus and unwanted embryos left over from in-vitro fertilisation clinics, based on informed consent of the embryo's "parents".
It also proposes to lay down guidelines restricting the way research is conducted once a moratorium on this research is lifted next month.
