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Science 25 November 2005:
Vol. 310. no. 5752, pp. 1327 - 1330
DOI: 10.1126/science.1116110
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Reports

SMEDWI-2 Is a PIWI-Like Protein That Regulates Planarian Stem Cells

Peter W. Reddien,* Néstor J. Oviedo,{dagger} Joya R. Jennings, James C. Jenkin, Alejandro Sánchez Alvarado{ddagger}

We have identified two genes, smedwi-1 and smedwi-2, expressed in the dividing adult stem cells (neoblasts) of the planarian Schmidtea mediterranea. Both genes encode proteins that belong to the Argonaute/PIWI protein family and that share highest homology with those proteins defined by Drosophila PIWI. RNA interference (RNAi) of smedwi-2 blocks regeneration, even though neoblasts are present, irradiation-sensitive, and capable of proliferating in response to wounding; smedwi-2(RNAi) neoblast progeny migrate to sites of cell turnover but, unlike normal cells, fail at replacing aged tissue. We suggest that SMEDWI-2 functions within dividing neoblasts to support the generation of cells that promote regeneration and homeostasis.

Howard Hughes Medical Institute, Department of Neurobiology and Anatomy, University of Utah School of Medicine, Salt Lake City, UT 84132, USA.

* Present address: MIT Biology, Whitehead Institute, Cambridge, MA 02142, USA.

{dagger} Present address: Cytokine Biology Department, Forsyth Institute, Harvard Medical School, Boston, MA 02115, USA.

{ddagger} To whom correspondence should be addressed. E-mail: sanchez{at}neuro.utah.edu

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