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Cellular Imaging

The Glow-in-the-Dark Brain
Brought to you by a jellyfish

Shelley Halpain makes bright, vivid movies of brain cells growing, and here's what she sees:

At first a brain cell looks like a fried egg. It quivers, then sends out tendrils. The tendrils wriggle, extend, and then retract, an out-and-back motion that Halpain describes as saltatory. You might just say they're salsa dancing.

One tendril becomes an axon, a conduit for transmitting signals to other brain cells. Axons explore their terrain intrepidly, hoping to link up with other cells. The rest of the tendrils become dendrites; they stay near home, waiting to spark a relationship with any axon that might come wandering by.

Halpain, a neuro-scientist at the Scripps Research Institute in San Diego, wants to figure out how a tendril knows to become an axon instead of a dendrite. What compels the brain to organize itself in such a fashion? Who's driving the bus?

These questions will likely take years of research to answer. In the meantime Halpain's movies take advantage of a tool that radically improves her ability to see brain cells developing in real time. It's a fluorescent protein from a jellyfish.

For years scientists had struggled to see how brain cells grow. Researchers had been chemically attaching fluorescent molecules to proteins, then injecting the concoctions into a cell, but this laborious process often killed the cell before experiments could even begin.

Then came Aequorea victoria, a glowing jellyfish that lives in the North Pacific. Scientists were able to isolate a fluorescent protein in Aequorea, and using their collective genius, they came up with a name for it: green fluorescent protein.

GFP, as it's more commonly called, is barrel-shaped and hollow in the center. Right smack in the middle is the fluorophore—the glowing part of the protein. (Did we say barrel? It's really a lantern.)

By 1995 researchers had figured out how to clone the gene that produces the protein and had developed a technique for successfully transferring the gene into brain cells so that they, too, would become intrinsically fluorescent. The gene is now manufactured in test tubes using bacterial cultures, and no jellyfish need be sacrificed on behalf of neuroscience.

No doubt people will continue to find creative and slightly weird uses for the protein lantern. Someone had the bright idea of genetically engineering a mouse that produces GFP throughout its body. Under certain lighting these mice glow faintly green. (You can see where this will lead. Coming soon to a mall near you: roving packs of fluorescent green teenagers.)

Even Hollywood has found clever ways to use GFP. Did you see the cameo by Aequorea at the beginning of Hulk? Now we know the Hulk's true color: jellyfish green.

—Joel Achenbach
    Washington Post staff writer

Web Links

Halpain Home Page
Shelley Halpain's lab website posts color photographs illustrating the structure of neurons as well as descriptions of the lab's ongoing projects.

Neuroscience for Kids
Professor Chudler of the University of Washington has compiled numerous exercises and activities for grades 3-12 designed to help students visualize various parts of the nervous system. There are even instructions for making a neuron costume for Halloween.

Basics of Neurobiology
Visit this interactive website for a discussion of neurobiology, including an in-depth description of neurons.

More Articles by Joel Achenbach

Military Theory and the Force of Ideas
As military technology becomes more and more advanced, there is less room for valor on the battlefield.

Rough Draft
Writer Joel Achenbach's column is gaining a cult following. It takes a sometimes humorous, sometimes eye-squinting, but always intelligent look at today's headlines, personal interests, and the little life-annoyances we all live with.

Free World Map

Dulbecco, Renato, ed. Encyclopedia of Human Biology, vol 12. Academic Press, 1991.

Herper, Matthew. "Biotech's Glowing Breakthrough." Available online at

Karlsson, Christina, and Jonathon Pines. "Green Fluorescent Protein," Cell Biology: A laboratory handbook, vol. 4. Academic Press, 1998.

Llinas, Rodolfo R., ed. The Biology of the Brain: From neurons to networks. W. H. Freeman & Company, 1988.

Mills, C. E. "Bioluminescence and other factoids about Aequorea, a hydromedusa." Available online at


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