By Richard Black World Service science correspondent

Scientists in Norway have managed to turn one sort of human cell into another in a novel way.

Conventional scientific wisdom has been: once a skin cell, always a skin cell.

All the evidence has been that nerve cells can only produce other nerve cells, muscle cells only produce other muscle cells, and so on.

But the experiments of researchers at the University of Oslo appear to show that adult cells are great deal more flexible.

'New treatments'

Writing in the journal Nature Biotechnology, the Norwegian team describes how it used chemicals found in the body to "re-program" cells derived from the skin (known as fibroblasts), and turn them into completely different cell types.

They suggest their research could eventually lead to new treatments for diseases such as diabetes, stroke and Parkinson's without the need for stem cells and the ethical problems associated with them.

The skin cells were incubated in extracts taken from nerve cells. The scientists say the skin cells started to look like nerves and even started activating genes which nerves use.

When the cells divided, the new cells still looked like nerves.

Similar changes occurred when the researchers put skin cells in with chemicals made by immune cells.

Cautious response

Although they have not yet checked that the new, re-programmed skin cells function as nerves or immune cells, the scientists say their discovery potentially points the way to new medical treatments which carry the same promise as stem cell treatments - but without the ethical complications.

If ordinary adult cells really can be re-programmed in this way, there is no reason in theory why cells from skin or hair could not eventually be used to replace damaged brain tissue, or rebuild a defective organ.

Using a patient's own skin cells would also help get over the problems associated with rejection whenever "foreign" tissues are implanted in the body.

Other researchers have described the finding as "exciting" - although they have emphasised that any medical treatments lie in the future.

The Oslo researchers plan to check how well their new cells function.