Transparent fish to make human biolo...( Zebrafish are genetically similar to...),Health

Zebrafish are genetically similar to humans and are good models for human biology and disease. Now, researchers at Children's Hospital Boston have created a zebrafish that is transparent throughout its life. The new fish allows scientists to directly view its internal organs, and observe processes like tumor metastasis and blood production after bone-marrow transplant in a living organism.

The fish, described in the February 7 issue of Cell Stem Cell, was created by Richard White, MD, PhD, a clinical fellow in the Stem Cell Program at Children's, with others in the laboratory of Leonard Zon, PhD.

The classic method for studying human diseases in animals is to allow the animal to get the disease, kill and dissect the animal, then ask, "what happened?" But in cancer and other fast-changing processes that traverse the body, this method is bound to miss something. "It's like taking a photograph when you need a video," says White, also an instructor of medicine at the Dana-Farber Cancer Institute.

Zebrafish embryos have enabled researchers to study disease in live organisms, since they are transparent. But zebrafish adults are opaque. "Everything after four weeks has been invisible to us," says White.

White's first experiment on the zebrafish examined how a cancer spreads. "The process by which a tumor goes from being localized to widespread and ultimately fatal is the most vexing problem that oncologists face," says White. "We don't know why cancer cells decide to move away from their primary site to other parts in the body."

White created a fluorescent melanoma tumor in the transparent fish's abdominal cavity. Viewing the fish under a microscope, White saw the cancer cells begin to spread within five days. He even saw individual cells metastasize, something that has not been observed, so readily and in real-time, in a living organism.

The spreading melanoma cells appeared to "home" to the
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