Scientists have made a discovery about the way cells develop that could pave the way for growing artificial organs and stimulating the body to develop tissue on demand.

A team of researchers from New York and Yale Universities have discovered that that some liver cells are generated from bone marrow.

Until now it has been thought that tissues in the developing embryo come from three types of cell layer.

Scientists thought that organs such as the liver were derived only from one of the three types, while bone marrow was derived from another.

The new study shows that in fact the process of cell development is more flexible than thought, and that immature cells might have the potential to develop into any kind of cell in the body.

If true, scientists might be able to develop techniques to isolate the immature cells - known as stem cells - before they start to develop specific characteristics, and use them to stimulate organ development in the body, or to create artificial organs in the test tube.

Whole-organ transplantation

Researcher Dr Neil Theise, from New York University School of Medicine, said: "If we can isolate these cells, we have targets for gene therapy and the possibility of stem cell transplantation, rather than whole-organ transplantation.

"There is also the possibility of expanding cells in culture and creating an artificial liver."

Using radiation, researchers completely destroyed the bone marrow of female mice and replaced it with marrow from male mice.

During the next six months, they discovered that up to 2.2% of mature liver cells (hepatocytes) in the female mice were derived from the donated bone marrow.

They identified the donor cells by the presence of the Y chromosome that is only found in males.

The researchers also demonstrated that severe injury is not necessary for the formation of mature liver cells from bone marrow cells.

A study published in May found that severe toxic injury to the liver provoked liver cell regeneration from bone marrow cells.

Dr Theise said the findings could help doctors to understand better how liver diseases begin and progress.

He said: "These insights may yield new avenues of research into disease intervention, rather than just rescue therapies once the liver is destroyed."

The research is published in Hepatology, the journal of the American Association for the Study of Liver Diseases.