St. Louis ? A tiny worm that can regrow its body if chopped into little pieces could help explain how human stem cells function and lead to better ways to manipulate them.

Researchers have discovered that a molecule gives the stem cells of the worm, known as a planarian, their regenerative power.

A planarian can grow an entire new worm from a tiny piece of any part of its body except for the pharynx (a digestive organ) and the region in front of the light-sensing eye spots.

Scientists have studied planarians for more than a century, but they have only had the techniques to investigate the molecular goings-on within the flatworm’s cells for less than a decade, said Peter Reddien, a developmental biologist at MIT and the Whitehead Institute in Cambridge, Mass.

“This is the first time this could be done in the history of science,” Reddien said. “One gets the sense that we’re at the beginning of a very interesting road.”

University of Illinois researchers Tingxia Guo and Phillip A. Newmark, along with Antoine Peters from the Friedrich Miescher Institute for Biomedical Research in Basel, Switzerland, used some new genetic tricks to discover a protein that helps maintain stem cells in their primordial state. Without it, the animals begin regenerating but run out of stem cells before they can grow into a whole animal.

The protein – bruno-like, or bruli for short – is part of a family of proteins that bind to RNA. RNA is a genetic molecule that helps translate instructions encoded in DNA into proteins. Some RNAs help determine when genes are turned on and off or regulate other functions in the cell. The researchers don’t yet know how bruli keeps stem cells from differentiating into other types of cells but speculate that it may pause production of some proteins involved in generating specialized cells.

All multi-celled animals have some form of stem cell that allows them to reproduce or replace old and damaged organs, said Alejandro Sanchez Alvarado, a Howard Hughes Medical Institute researcher at the University of Utah.

Some of the key processes that control stem cells in planarians are likely to work in human stem cells as well, particularly in long-lived adult stem cells. Proteins related to bruli are found in virtually all animals and may play similar roles in maintaining stem cells, he said.

Although humans don’t regrow limbs or most complex organs – with the possible exception of the liver – people have supplies of stem cells that make new blood, skin, bone, olfactory neurons or renew the lining of the intestines.