Scientists have discovered a key biological safeguard that helps one of nature’s most impressive regenerators, the planarian flatworm, correctly rebuild its organs. 

The new research, published in Nature Communications on Feb. 23, illuminates how these animals prevent their powerful stem cells from making mistakes during regeneration, a discovery that may eventually help scientists understand how to better control stem cell behavior in other species.

Planarians are famous for their ability to regrow entire body parts, thanks to a vast pool of adult stem cells capable of turning into almost any cell type. But until now, researchers didn’t fully understand how these cells choose the right identity at the right time. “Very little has been known about the signals that instruct these stem cells to differentiate into specific cell types,” says senior author Carolyn Adler, associate professor in the Department of Biomedical and Translational Science, in the College of Veterinary Medicine.

To investigate this question, Adler and her team took advantage of a previous study that had used RNAi knockdown, a gene silencing technique, on a gene called roundabout A (RoboA), which caused the formation of an extra pharynx (or feeding tube) in the wrong place: the flatworm’s brain. “By tracing the origin of this phenotype back to stem cells, we found that RoboA normally suppresses stem cells in the brain from adopting the wrong fate,” Adler says. 

RoboA is a receptor, (a protein that straddles the inside and outside of a cell to relay external signals into cells) acting as a molecular guide to prevent stem cells from activating the wrong program. It does this by regulating the activity of another protein, FoxA, which directs pharynx‑specific cell types.

When Adler’s team knocked out the FoxA protein, they found that the planarian pharynx began producing neuron types normally found only in the head. “This suggests that stem cells carry a hidden flexibility to switch fates if the usual signals break down,” Adler says. “The findings reveal just how delicately balanced regenerative systems must be to rebuild organs accurately.”

Adler’s team next wanted to know what signals RoboA responded to, and zeroed in on Anosmin, a poorly understood protein found in humans but not in other mammals. Adler found that RoboA and Anosmin work together locally in the planarian brain to ensure the cells there form correctly. “Our results point to a new function for Anosmin in regulating stem cell fate choice,” says Adler.

Interestingly, Adler’s study is one of the first to elucidate the mechanisms of routine stem cell activity in adult animals. “We’ve known how this process works during development or during regeneration, when organs are just being established,” Adler says. “But it was exciting to discover that the mechanism occurs continuously throughout an animal’s life.”

Overall, the study shows that regeneration isn’t just about raw stem‑cell power. “It depends on a finely tuned conversation between cells, guided by molecular cues that keep identity decisions on track,” Adler says. “By linking specific extracellular signals to stem cell fate control, the work deepens our understanding of how highly plastic cells maintain precision during whole‑body regeneration.”

Lauren Cahoon Roberts is director of communications for the College of Veterinary Medicine.