Embryonic stem cells can give rise to virtually any tissue in the body. Scientists believe they may offer treatments for diseases like Parkinson's and diabetes and spinal cord injuries.
But to harvest the cells, human embryos must be destroyed. Some religious groups and others oppose that.
The new research into testicular cells, published online Friday by the journal Nature, comes from Dr. Gerd Hasenfuss of the Georg-August-University of Goettingen in Germany and colleagues.
Lab tests found that the mouse cells closely mimicked the behavior of embryonic stem cells, Hasenfuss said Friday. He said he is optimistic about finding human testicular cells that will do the same. Work has already begun on that, he said.
If such cells are found in men, "then we have resolved the ethical problem with human embryonic stem cells," he said in a telephone interview.
That would also open the door to removing testicular cells from a male patient, growing some tissue the patient needs, and transplanting that tissue into the same man without fear of biological rejection, he noted.
The mouse cells were found to give rise to a variety of specialized cells in the lab, including heart cells that contracted and nerve cells that produced dopamine, the chemical messenger that Parkinson's patients lack, he said.
Cells typical of the liver, skin, pancreas and blood vessels were produced as well, he said.
Meanwhile, in the United States, a transplant-free approach to curing Type 1 diabetes using medication has been reaffirmed in tests on mice, according to a Washington University study.
The study, published this week in the journal Science, shows that there is a period of time in mice after the onset of diabetes when drugs can stop the immune system from attacking all the insulin-producing cells in the pancreas.
"You have a window of time in humans, too," said Dr. Emil Unanue, the study's author and Washington University immunologist.
The study advances a transplant-free approach to curing Type 1 diabetes with a short and inexpensive drug treatment.
The research also rebuked Harvard University research from three years ago that said adding adult stem cell proteins from the spleen into the mouse pancreas could create new pancreatic cells.
Dr. Denise Faustman, author of the Harvard study in 2003, said she was excited about the research advancing.
She said introducing spleen cells could have provided the protein that helps kill T-cells and not created a new source of pancreatic cells, as her study suggested.
As many as 3 million diabetes cases are Type 1, according to the Juvenile Diabetes Research Foundation.
Type 1 diabetes is commonly a juvenile disease where immune system T-cells kill insulin-making pancreatic cells that control blood sugar levels.
Researchers hope medication can eliminate the need for pancreatic cell transplants that have been done on about 500 people and require long-term drug treatment.