Peter Reddien: Making heads or tails of it

© 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 of the excitement for me, but also entirely part of the challenge."

Sánchez Alvarado says that Reddien was undaunted by the heap of unique information the two had generated. "Anybody else would have looked at this data and would have been completely overwhelmed," he says. "This is where Peter shined."

After the RNAi paper, Reddien explored the function of one gene, smedwi-2, and found that it helps instruct S. mediterranea's stem cells so proper regrowth follows the amputation of body parts. ³

Reddien is no stranger to worms. He earned his PhD at Massachusetts Institute of Technology in Robert Horvitz's lab, where he studied the genetics behind programmed cell death in Caenorhabditis elegans. Though Reddien says his approach to science was heavily influenced by the open and rigorous atmosphere in Horvitz's lab, he left C. elegans genetics behind in 2002 and ventured into foreign waters for his postdoc. "It felt like it was going to be a bit of an adventure and also a bit of a risk," Reddien says. "Regeneration felt like a real frontier."

Now in his own lab at MIT's Whitehead Institute for Biomedical Research, Reddien continues to push forward into this frontier. In January, Petersen and Reddien published a paper in Science in which they unveiled their six-headed planarian and described its genesis. The two showed that an S. mediterranea gene, Smed-bcatenin-1, gives the flatworm the ability to correctly regrow a lopped-off tail or other posterior-facing body part, solving a piece of the regeneration polarity puzzle, which has vexed developmental biologists for years.

"We're at the beginning of an exciting road," says Reddien. "We're going to follow our noses and our curiosity and see where it leads us."

Sánchez Alvarado says he has high expectations for his former postdoc. "Everything that he'll do, he'll do with the same rigor and insightfulness that he has so far with everything else he's pursued." he says. "I'm hoping that Peter will be one of the cornerstones of this whole endeavor."