The Zebrafish, which can completely regenerate its severed spinal cord, might hold promise for research into tissue repair in humans, researchers said. Scientists are looking at one protein in particular that is key to this accomplishment in the fish.
A bridge forms
"This is one of nature's most remarkable feats of regeneration," said the study's senior investigator Kenneth Poss, a professor of cell biology at Duke University.
"Given the limited number of successful therapies available today for repairing lost tissues, we need to look to animals like zebrafish for new clues about how to stimulate regeneration," said Poss, whose study was published in the journal Science.
When the severed spinal cord of the zebrafish undergoes regeneration, a bridge forms.
Nerve cells follow and within eight weeks new nerve tissue has plugged the gap, allowing the fish to reverse their paralysis completely, the Poss team reported.
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To figure out what is going on, scientists searched for all of the genes whose activity abruptly changed after spinal cord injury.
Seven of these were found to code for proteins secreted from cells.
Many shared genes
One of these proteins, called CTGF – connective tissue growth factor – was intriguing because its levels rose in supporting cells that formed the bridge in the first two weeks following injury.
When the protein was deleted genetically, those fish failed to regenerate.
People and zebrafish share many genes, and human CTGF protein is nearly 90 percent similar in its amino acid components to that of zebra fish.
Inserting human CTGF into the injury site in fish helped the regeneration process.
"The fish go from paralysed to swimming in the tank. The effect of the protein is striking," said Mayssa Mokalled, a postdoctoral fellow in Poss's group.
But CTGF alone is probably not enough for people to regenerate their spinal cords, the team said. The process is more complex in mammals, in part because scar tissue forms around an injury.
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Future studies will look at mice to determine which of their cells express CTGF, the team said. Researchers also plan to look at other proteins involved in the regeneration process in zebrafish.
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