A protein related to RNA interference (RNAi) machinery appears to regulate how the adult stem cells differentiate in planarians, scientists reported in the November 25Science. Relatives of the protein, SMEDWI-2, are highly conserved across plants, yeast, and humans, and additional studies of the protein's structure and functioning could shed light on how adult stem cells are regulated in general, according to senior author Alejandro Sanchez Alvarado.

"While many regulators of embryonic stem cells have been identified, the same cannot be said for adult somatic stem cells, where our understanding of their maintenance and regulation are not as well worked out," Sanchez Alvarado, based at the University of Utah in Salt Lake City, told The Scientist.

Members of the highly conserved PIWI/Argonaute proteins are key components of RNAi pathways. They also are linked to germline stem cells, but "little to nothing is known about the role of...

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