<figcaption> Credit: © laura barisonzi photography</figcaption>
Credit: © laura barisonzi photography

For his 33rd birthday last year, Massachusetts Institute of Technology geneticist Peter Reddien received a special gift from his students: a t-shirt imprinted with a picture of a six-headed flatworm. Reddien and his postdoc, Christian Petersen, had recently created the altered planarian, Schmidtea mediterranea, by using RNAi to silence a gene critical to proper regeneration and then amputating parts of the worm's body.1 Where a normal worm would have replaced posterior body parts normally, this one grew only extra heads.

Reddien started studying regeneration as a postdoc at the University of Utah. He and mentor Alejandro Sánchez Alvarado, who studies the genetics of planarian regeneration, used RNAi to silence 1,065 genes in S. mediterranea. They recorded about 240 resulting phenotypes - among them sideways movement and the development of extra photoreceptors.2 "No planaria phenotype had been published," Reddien remembers. "That was part...

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