Fish Hot on the heels of see-through frogs, researchers at Children’s Hospital Boston have bred see-through zebrafish that put tumors and stem cells on display as they grow. The transparent lab animals already have started to provide insights into how cancer spreads – and how it can be treated – in not-so-transparent human beings. The fish breeding project and its application to medical research are described in Thursday’s issue of the journal Cell Stem Cell as well as a news release from Children’s. Zebrafish, like frogs and mice, are frequently used as experimental models for diseases and biological processes seen in humans as well.

Usually, researchers allow the animals to get a disease analogous to the human malady, then kill and dissect the animal. But when it comes to cancer progression, scientists would prefer to see how the process works in a live animal. Scientists have used transparent zebrafish embryos for that purpose, but when the fish reach adulthood, they turn opaque. That effectively closes the shutters over a valuable window for research. “Everything after four weeks has been invisible to us,” Dr. Richard White, a clinical fellow in Children’s stem cell program and an instructor of medicine at the Dana-Farber Cancer Institute, explained in today’s news release.

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