See-Through Fish Could Reveal Origins of Neuroblastoma

(Credit: Tohru Murakami)

A new type of zebrafish that produces fluorescent tags in migratory embryonic nerve precursor cells could help researchers find the origins of the third-most common pediatric cancer in the U.S.

The research is published in the jornal Genesis. 

“You can see they’ve already started to migrate that way, and a lot of them are transitioning,” Rosa Uribe says in her office as she traces the movements of green neural crest cells in a time-lapse movie playing on her computer.

In humans, neural crest cells are the point of origin for neuroblastoma, a common pediatric cancer, and Uribe’s hoping the new fish can provide clues the disease.

“You can see that a lot of them are transitioning,” she says of the cells on her screen. “Some of them are dividing there, there, there. And then they turn off the green, which means they’re done dividing.”

Why the cells stop dividing is one of the key questions she hopes to answer. SOX10 is one of more than 20 varieties of SOX proteins, and all of them regulate rapid cell division in fast-growing embryos. The same SOX proteins are also often found activated in cancer cells. Finding the “off” switch for SOX10 in neural crest cells could potentially lead to treatments for cancers where SOX proteins play a role, she says.

Uribe also studies the enteric nervous system — another area of focus for her lab — which forms from neural crest cells.

“Neural crest cells are stem cells that form from the earliest portion of our central nervous system, the neural tube,” says Uribe, an assistant professor of biosciences at Rice University. “They express SOX10 in addition to a bunch of other really important genes.”

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To view neural crest cells during embryonic development, Uribe’s team keeps a stock of breeder fish in a state-of-the-art fish room with hundreds of tanks. They remove the embryos — for the new reporter line and more than a dozen others — from the tanks by hand each day and bring them to the laboratory for observation.

The researchers use zebrafish for the studies for several reasons. First, SOX and many other genes in the fish are virtually identical to genes that serve the same basic roles in humans. Second, biologists have amassed a huge body of knowledge about zebrafish, which have been studied as a model organism for decades.

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Finally, zebrafish breed and develop quickly—a new batch of embryos can be studied each day in Uribe’s lab—and the fish are transparent, which means researchers can watch what’s happening inside them while they are alive.

Using a variety of methods and microscopes, Uribe and her students immobilise live embryos and take photographs to trace their development over a period of hours. For example, the researchers tracked and observed the neural crest cells, which first appear in zebrafish embryos about 12 hours after fertilization, for up to four hours.

“Neural crest cells also do something else that’s relevant to cancer,” Uribe says. “They undergo something called the epithelial-to-mesenchymal transition, or EMT, shortly after they form, and this is what allows them to break away and migrate to the various places in the embryo.”

EMT is important for embryonic development because it allows cells to revert backwards along their developmental path and become more stem-like. This malleability allows embryonic cells to form new tissues, but researchers have found many metastatic cancers that use the same genetic circuitry.

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Metastasis, or the spread of cancer to other parts of the body, causes more than 90% of cancer deaths. EMT is the switch many cancer cells employ to break away and become metastatic.

Having the ability to observe neural crest cells from the moment they form until they finish migrating is one key to understanding them. Uribe’s team will use the new cell line for this, in addition to others that have different coloured tags for different reporter genes.

They’ll also mix and match genes in new strains of zebrafish to test what happens when cells make either too much of a specific protein or too little. Uribe’s lab will use a variety of techniques for this, including CRISPR-Cas9.

Microscopes capable of gathering time-lapse images of the variously coloured glowing cells are also critical, and Uribe’s lab has seven of them.

These include a state-of-the-art robotic instrument with tiny hoses and pumps that can draw a single embryo from a numbered test chamber up through a hose, transport it to the microscope focal plane, bring it into focus, rotate it for photos from any angle and then return it and repeat the process for up to 95 more embryos.

“For the migration time-lapse images there is software that’s capable of following individual cells for hours,” Uribe says. “We can get angles and trajectories, maps of routes taken by one cell or groups of cells, and we can get quantitative data, like velocities and proliferation rates.”

Researchers at the University of Illinois at Chicago and Caltech also contributed to the work. 


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