Last updated January 16, 2018 at 2:30 pm
Why are some fish, amphibians and reptiles able to regenerate their spinal cords after injury while mammals can’t? A new study has investigated the genetic switches involved in the process in the lamprey, an ancient jawless fish that can fully recover function from a severed spinal cord within months.
“They can go from paralysis to full swimming behaviors in 10 to 12 weeks,” says Jennifer Morgan, director of the Eugene Bell Centre for Regenerative Biology and Tissue Engineering in Massachusetts, and one of the authors of the new study.
Previous studies have looked at the recovery process in other animals like zebrafish, frogs or salamandars, but the researchers picked lampreys as they are very evolutionarily distant from humans, branching off around 550 million years ago.
Lampreys are incredibly ancient vertebrates, so investigating the genes involved in this species can identify the most highly conserved pathways through evolution.
“Scientists have known for many years that the lamprey achieves spontaneous recovery from spinal cord injury, but we have not known the molecular recipe that accompanies and supports this remarkable capacity,” said Dr. Bloom, associate professor at the Feinstein Institute and associate professor and director of research at the Zucker School of Medicine at Hofstra/Northwell.
“In this study, we have determined all the genes that change during the course of recovery in the lamprey. Now that we have that information, we can use it to test if specific pathways are actually essential to the process.”
The researchers used a large-scale gene expression analysis to track which genes were turned on and when through the course of the lampreys healing process. They found a large overlap with genes that are switched on in mammals, including humans, in response to injuries in the peripheral nervous system.
Importantly, the researchers sampled not only the tissue around the injured are of the spinal cord, but also the brain, where they saw rapid, robust and long-lasting changes in gene expression after injury.
“This reinforces the idea that the brain changes a lot after a spinal cord injury,” says Jennifer Morgan. “Most people are thinking ‘What can you do to treat the spinal cord itself?’ but our data really support the idea that there’s also a lot going on in the brain.”
Many of the genes switched on in the healing process are part of the Wnt signalling pathway, which is known to play a role in embryo development, maintaining adult tissue, and even in cancer.
If the lampreys were treated with a drug that blocked this pathway, they never recovered their ability to swim. The next stage in this research will explore why this pathway is so important in the healing process.
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