Stem cells taken from human embryos were coaxed into becoming motor neurons in an experiment that might one day help scientists repair damaged nervous systems, researchers reported Sunday.

The study supports claims by stem cell researchers that they can train embryonic stem cells to develop on demand into any type of tissue in the body.

They hope this technology will eventually transform medicine and allow cures for a range of diseases - in this case, nervous system injuries and diseases such as Lou Gehrig’s disease.

The team at the University of Wisconsin used stem cells that are approved for research by the federal government. Their experiment was funded by the National Institutes of Health and the Amyotrophic Lateral Sclerosis Association, which is seeking a cure for the untreatable and paralyzing condition also known as Lou Gehrig’s disease.

Dr. Su-Chun Zhang and colleagues said their trial-and-error study helped them learn how motor neuron cells, which are key to the nervous system, develop in the first place.

Motor neurons transmit messages from the brain and spinal cord and help control almost every movement in the body.

Patients with motor neuron diseases or spinal cord injuries lose control of these movements.

The hope is to repair or replace these damaged cells.

Writing in the journal Nature Biotechnology, Zhang and colleagues said they delivered a carefully timed combination of proteins to their cells to direct their development.

“You need to teach the (cells) to change step by step, where each step has different conditions and a strict window of time,” Zhang said in a statement. “Otherwise, it just won’t work.”

And Zhang said the experiment showed that human stem cells do not necessarily differentiate in the way that other animal stem cells do.

“We cannot simply translate studies from animal to humans,” Zhang said.

The Bush administration does not support the use of human embryonic stem cells except in limited circumstances using cells already in existence as of 2001. Federal funds may not be used to take new stem cells from human embryos, which are destroyed in the process.

Opponents of human embryonic research say this is tantamount to murder, while supporters say embryos from fertility clinics are slated for destruction anyway and point to the potential benefits from research.

The issue is further complicated by a study reported last week that found stem cell lines from human embryos, which are grown with animal-derived cells, have become contaminated with a product that human cells are genetically unable to make - meaning that these contaminated cells could be dangerous if used in people.

All human embryonic stem cell lines currently approved for study under federal funding in the United States have been grown on or derived from a so-called feeder layer of mouse cells.