If you trace our evolutionary tree way back to its roots — long before the shedding of gills or the development of opposable thumbs — you will likely find a common ancestor with the amazing ability to regenerate lost body parts.
Lucky descendants of this creature, including today’s salamanders or zebrafish, can still perform the feat, but humans lost much of their regenerative power over millions of years of evolution.
In an effort to understand what was lost, researchers have built a running list of the genes that enable regenerating animals to grow back a severed tail or repair damaged tissues. Surprisingly, they have found that genes important for regeneration in these creatures also have counterparts in humans. The key difference might not lie in the genes themselves but in the sequences that regulate how those genes are activated during injury.
A Duke study appearing April 6 in the journal Nature has discovered the presence of these regulatory sequences in zebrafish, a favored model of regeneration research. Called “tissue regeneration enhancer elements” or TREEs, these sequences can turn on genes in injury sites and even be engineered to change the ability of animals to regenerate.
“We want to know how regeneration happens, with the ultimate goal of helping humans realize their full regenerative potential,” said Kenneth D. Poss, Ph.D., senior author of the study and professor of cell biology at Duke University School of Medicine. “Our study points to a way that we could potentially awaken the genes responsible for regeneration that we all carry within us.”
Over the last decade, researchers have identified dozens of regeneration genes in organisms like zebrafish, flies, and mice. For example, one molecule called neuregulin 1 can make heart muscle cells proliferate and others called fibroblast growth factors can promote the regeneration of a severed fin. Yet, Poss says, what has not been explored are the regulatory elements that turn these genes on in injured tissue, keep them on during regeneration, and then turn them off when regeneration is done.
In this study, Poss and his colleagues wanted to determine whether or not these important stretches of DNA exist, and if so, pinpoint their location. It was already well known that small chunks of sequence, called enhancer elements, control when genes are turned on in a developing embryo. But it wasn’t clear whether these elements are also used to drive regeneration.
The green signal in these images of an injured zebrafish heart and a fin indicate the activity of a gene that enhances tissue regeneration.
Credit: Junsu Kang, Duke University