Flatworm Gene For Stem Cell Differentiation Identified

Flatworm Gene For Stem Cell Differentiation Identified

Researchers have identified a gene responsible for stem cell differentiation in a flatworm (planarian) which is frequently studied for its regenerative properties. The research was done at the University of Utah Health Sciences Center. According to the press release on EurekAlert,

Cut one of these animals in half, and a week later, two fully functional worms will have developed from the pieces. Cut a piece that is 1/279th the size of the animal, and it too will regrow into a complete worm. The process, scientists know, is dependent on stem cells in the adult planaria known as neoblasts.

The scientists, who had done a previous study turning off certain genes in the planaria, found in this study that the smedwi-2 gene, which is active in dividing neoblasts, is crucial to stem cell differentiation. They used RNA interference to turn the gene off. When a normal planarian is exposed to radiation that destroys the neoblasts, the animal begins to actually degenerate in a specific pattern and lose its ability to regenerate. The worms that had the smedwi-2 gene deactivated degenerated the same way the irradiated worms do.

The story as reported in Science Daily adds

The researchers postulated three theories why the worms could not regenerate or maintain cells after smedwi-2 was silenced:

• The stem cells were not responding to tissue damage or homeostasis signals.
• The stem cell division progeny failed to migrate to the appropriate tissues.
• The daughter cells didn't know how to differentiate.

The team found that the stem cells were competent to robustly respond to amputation by significantly increasing their proliferation as well as to home to tissues undergoing homeostasis. But the researchers also found that once the daughter cells reach their target tissues, they were unable to properly differentiate.

The smedwi-2 gene is part of a protein family similar to PIWI genes, which have been shown to play a role in regulating stem cells. When neoblasts, like other stem cells, divide, they form a copy of the original and a daughter cell that has the capacity to become a different type of cell. The researchers speculated that the PIWI proteins are necessary for the daughter cells to differentiate and are not the mechanism required for the original stem cell itself to divide. It is not yet known if the PIWI proteins serve the same fuction in human stem cells, but the research is suggestive.

The story is also reported in the Salt Lake Tribune, with the press release also showing up with slight variations on RxPG News. The Howard Hughes Medical Institute has a cool picture of planaria with their report.