Stem cells could be used to treat diabetes, scientists suggest.
Many diabetes need to inject insulin
Research has already indicated stem cells could be used to treat conditions including brain damage, multiple sclerosis and sickle cell anaemia.
This latest study found stem cells from bone marrow could be converted into insulin-producing beta cells in the pancreas to replace those damaged by diabetes.
The hormone insulin is needed by the body to regulate blood sugar levels.
People with type-1 diabetes have lost the ability to make insulin because beta cells found in groups called islets of Langerhans in the pancreas have been destroyed.
There is a lot of work to be done before this procedure could be used in practice
Dr Eleanor Kennedy, Diabetes UK
They rely on regular insulin injections to control their blood sugar levels and keep them healthy. They also have to avoid very sugary foods.
Those with Type 2 diabetes have beta cells, but the cells cannot secrete enough insulin or do not produce enough.
The researchers genetically modified bone marrow cells from male mice to produce a protein which gives cells a fluorescent glow when they are near activated insulin genes.
These were then transplanted into female mice whose bone marrow had been destroyed by radiation.
Researchers examined the mice four to six weeks later, and found a small number of the glowing green cells in the pancreatic islets of Langerhans.
They were the cells which had come from the bone marrow and they were behaving in exactly the same way as beta cells, producing insulin in response to glucose.
These cells all contained the Y chromosome, which could only have come from the male mice.
The researchers say more research is needed, despite the promising results from this study.
Only a small proportion of beta cells in the female mice - at most 3% - came from transformed bone-marrow stem cells.
The scientists say they also need to know more about how the bone marrow cells become beta cells.
However, the research suggests it could eventually be possible to harvest bone marrow cells from people with diabetes, genetically modify them, and transplant them back without fear of rejection by their immune system.
Although the researchers, from the New York University School of Medicine, say their findings cannot help diabetics immediately, they say it may one day be possible to produce unlimited quantities of insulin-producing cells culled from bone marrow.
Finding a source of replacement cells is a key aim of diabetes research.
Doctors have carried out successful islet transplants, but there is a limited supply, and patients need to take strong immunosuppression drugs to make sure their bodies do not reject the transplants.
Mehboob Hussain, assistant professor of medicine and pharmacology, who led the study, said: "Clearly much work remains to be done.
"But I am absolutely excited by the potential applications of our findings. In our body, there is an additional, easily accessible source of cells that are capable of becoming insulin-producing pancreatic endocrine cells.
"Transplantation of bone marrow stem cells already is a routine procedure for treating cancer and other diseases, and we could build on that experience."
Dr Eleanor Kennedy, research manager at Diabetes UK said: "This is very interesting work in an exciting area of diabetes research.
"Theoretically, pancreatic beta cells produced from a patient's own bone marrow could be used to treat diabetes, overcoming the requirement for immunosuppression following islet transplantation.
"However this research is in its early stages and there is a lot of work to be done before this procedure could be used in practice."
The research is published in the Journal of Clinical Investigation.