In rivers and streams throughout the globe lives a tube-shaped carnivore. It paralyzes and captures prey with a crown of tentacles, then attracts it in by way of its mouth (which additionally serves as its anus). This unsettling creature is a hydra, a freshwater-dwelling cnidarian not more than a half-inch lengthy that eats largely insect larvae and crustaceans. A hydra’s look and consuming habits alone give it a sci-fi really feel, however its potential to regenerate its physique — even its head — from solely a scrap of tissue or pile of cells raises it to one other stage.
“It’s one of these organisms that’s thought to never die unless you try to kill it or, you know, starve it to death,” Ali Mortazavi, a developmental biologist on the University of California, Irvine, stated. A hydra’s regenerative skills permit it to continually exchange bits of itself, so it doesn’t succumb to issues like previous age or illness. Aside from the immortality perk, fixed regeneration means a hydra doesn’t have to sweat the small stuff, like shedding physique components. Give it a few days and it’ll develop again something.
Dr. Mortazavi and his colleagues have taken a massive step in understanding how a hydra regenerates its head. Their analysis was printed in Genome Biology and Evolution on Wednesday.
To examine what makes this exceptional feat doable, the researchers checked out adjustments in gene expression — whether or not a gene is copied from DNA into RNA — all through the course of hydra head regeneration. This management of gene expression is known as epigenetic regulation. Hydras have a genome quite similar to that of species with little regenerative capability, like humans, so it’s thought that epigenetic regulation performs a main function in making the hydra’s powers of regeneration doable.
The group found dynamic alterations within the regulation of stretches of DNA referred to as enhancers. Enhancers improve the chance that a associated gene can be copied from DNA into RNA. These enhancers have been serving to to make sure the expression of many genes, the group discovered, together with these lengthy recognized to be vital for regeneration. “Nobody knew hydras had these enhancer regions,” stated Dr. Mortazavi, who famous that the examine put hydra in the identical membership as many different animals, together with mammals.
The researchers then in contrast gene expression throughout head regeneration with gene expression throughout budding, a type of asexual replica the place a hydra grows a polyp that’s principally a copy of itself. That course of requires development of a second head, however the researchers discovered that a budding head varieties in a very totally different approach from a head regrowing after harm.
“When I took a look at the trends in gene expression, the genes are kind of increasing slowly throughout the budding head development, but in regeneration, we noticed these sharp turns,” stated Aide Macias-Muñoz, a developmental biologist at University of California, Santa Barbara, who was one of many examine authors. “A lot of genes are being turned on and then turned off and then turned back on. So even though the end result is the same, it looks like the trajectory is actually very different.”
Dr. Mortazavi was additionally stunned to discover that gene expression timing diverse a lot between head regeneration and budding. “Clearly there’s more than one way to make a head,” he stated.
The discovery of those enhancer areas and their function in hydra head regeneration additionally means that the evolution of enhancers predates the evolutionary divergence of cnidarians and bilaterians (animals with bilateral symmetry, like people) round 750 million years ago. Erin Davies, a developmental biologist on the National Cancer Institute who research regeneration however was not concerned within the work, sees these findings as a reminder of the significance of learning historical creatures like hydras.
“They are really in a prime position for answering a lot of very fundamental questions in developmental biology,” she stated, together with “How did nervous systems evolve? How did you get bilateral symmetry?”
This sort of work can be important for the regenerative drugs subject, Dr. Davies stated, the place a common goal is to restore diseased and injured tissues and even complete organs.
“If you have a good handle on a paradigm in any animal system,” she stated, “then you can start to think about how you might reverse engineer things in less regeneration-competent species, like mammals.”
