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When smedwi-2 gene is silenced, regeneration stopped in planarians. This silenced gene in worm shows a key role in regeneration.
Researchers at the University of Utah have discovered that when a gene called smedwi-2 is silenced in the adult stem cells of planarians, the quarter-inch long worm is unable to carry out a biological process that has mystified scientists for centuries: regeneration.
The study published in the Nov. 25 issue of Science was led by Alejandro Sánchez Alvarado, Ph.D., Howard Hughes Medical Institute investigator and professor of neurobiology and anatomy at the U of U School of Medicine, and carried out by members of his laboratory, in particular Helen Hay Whitney Foundation post-doctoral fellow Peter W. Reddien who is now an Associate Member at the Whitehead Institute for Biomedical Research.
Elimination of smedwi-2 not only leads to an inability to mount a regenerative response after amputation, but also to the eventual demise of unamputated animals along a reproducible series of events, that is, regression of the head tip, curling of the body and tissue disintegration. These defects are very similar to what is observed after the planarian stem cells are destroyed by lethal doses of irradiation. The key difference, however, is that the irradiation-like defects observed in animals devoid of smedwi-2 occur even though the stem cells are still present in the organism.
"The smedwi-2 molecule is doing something early in the specification of stem cell progeny that modulates their ability to differentiate into the proper cell type," Sánchez Alvarado said. How this molecule is modulating stem cells is one of the next steps that he and Reddien are trying to solve. The answer could have far-reaching implications, because genes similar to smedwi-2 are found in plants, animals and human beings.
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