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Learning Curve
Reddien discovered Morgan’s work during his graduate studies. That quickly led him to Sánchez Alvarado and Newmark’s 1999 Proceedings of the National Academy of Sciences paper on the RNAi work.
“The things they had shown gave me hope that turning planarians into a molecular model organism would work,” Reddien recalls. “They were bold with their choices and had taken a massive risk.”
Reddien joined Sánchez Alvarado as a postdoc at the Utah laboratory and his first task was to use RNAi for a large screen of planarian genes. It was still unclear if this approach could silence genes well enough to show phenotypes—that is, to show physical or behavioral defects, such as improper regeneration in a worm.
He first chose to test 30 genes from a list of nearly 4,000 genes cloned and sequenced at Carnegie but was disappointed to see no defects in the first trial. He speculated that perhaps the worms had to go through two rounds of regeneration before defects would appear. That did the trick.
“This is the type of science you dream about as a kid. We are studying processes that are dramatically and broadly important.”
Peter Reddien
“I started seeing phenotypes,” he says. “Animals would fail to regenerate, or were paralyzed, or had weird lesions all over their bodies. It was very dramatic and very exciting.” So much so, the entire lab headed to Squatters brew pub in Salt Lake City for a celebratory Champagne toast.
Not all of Reddien’s postdoc time went so swimmingly, however. Working with a worm virtually unknown in molecular circles and handled by only a few labs around the world had its headaches.
Reddien played with tricking the worms into gobbling up the bacteria that produced the double-stranded RNA. He also made trips to an art supply store to find the best materials, like heavy black paper, for taking photographs of the semitranslucent worms through the microscope.
“That was part of the fun and adventure for me, but it was also very challenging,” says Reddien, now at Massachusetts Institute of Technology’s Whitehead Institute for Biomedical Research. “There is no protocol book that you can just pull out and implement. We have to start from scratch each time we would like to use a new method.”
Reddien eventually optimized the RNAi to do a large-scale screen to knock down 1,065 planarian genes and search for defects. Reddien and two lab mates made more than 53,000 amputations to worms with a razor blade during the screen. They found 240 genes that when silenced produced some kind of defect; 85 percent of these genes are conserved in other animals, including humans.
As a model organism, the goofy-looking flatworm had arrived at a critical juncture. “I was getting the first collection of planarian phenotypes the world had ever seen,” recalls Reddien. The work was published in Developmental Cell in 2005.
With the molecular tools in hand to light up, track, and silence the planarian’s stem cell genes, as well as much of its genome completed (a project also spearheaded by these three), the scientists could begin to map genes onto the key stages of regeneration. They could move on to the tasks that really charged them up: finding genes that give the neoblast cells their stem cell identity, genes that direct them to respond to a wound, genes that help form the regeneration stump, or blastema, and—most intriguing of all—genes that tell the animal which body part is missing.
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