The Chernobyl nuclear power plant disaster in 1986 left the surrounding area with the dubious distinction of being the most radioactive landscape on Earth. However, the recent discovery of a worm species thriving in this highly irradiated environment is seen as a potential breakthrough for cancer research.
Despite the evacuation of humans following the meltdown of Reactor 4, numerous plants and animals continued to inhabit the region, adapting to the persistently high radiation levels that endure to this day.
In recent years, researchers have observed physical and genetic differences in some of the animals residing in the Chernobyl Exclusion Zone compared to their counterparts elsewhere. This has raised significant questions about the long-term impact of chronic radiation exposure on DNA.
A new study led by researchers at New York University (NYU) has shed further light on this phenomenon. They found that the genomes of microscopic worms living in the Chernobyl region have remained largely unaffected by chronic radiation exposure. This resilience suggest an extraordinary adaptability among these invertebrates to their hostile environment.
The implications of this discovery extend beyond the realm of worm biology. It offer valuable insights into the mechanisms of cancer development in humans, particularly those with a genetic predisposition to the disease. By understanding how organisms like these worms cope with radiation-induced stress without genetic damage, researchers hope to unravel the mysteries of cancer susceptibility in humans.
Sophia Tintori, a postdoctoral associate in the Department of Biology at New York University and the first author of the study that was published in the Proceedings of the National Academy of Sciences (PNAS) said, “Chernobyl was a tragedy of incomprehensible scale, but we still don’t have a great grasp on the effects of the disaster on local populations.”
“Did the sudden environmental shift select for species, or even individuals within a species, that are naturally more resistant to ionizing radiation?”
Tintori and her team opted to study nematodes, diminutive worms characterized by their uncomplicated genomes and swift reproductive cycles, rendering them especially valuable for investigating fundamental biological processes.
Matthew Rockman, a professor of biology at NYU and the study’s senior author, said, “These worms live everywhere, and they live quickly, so they go through dozens of generations of evolution while a typical vertebrate is still putting on its shoes.”
“I had seen footage of the Exclusion Zone and was surprised by how lush and overgrown it looked—I’d never thought of it as teeming with life. If I want to find worms that are particularly tolerant to radiation exposure, this is a landscape that might have already selected for that,” added Tintori.
In 2019, Tintori and Rockman, in collaboration with scientists from Ukraine and colleagues from the United States, including biologist Timothy Mousseau from the University of South Carolina, embarked on a visit to the Chernobyl Exclusion Zone. Their objective was to investigate whether the chronic radiation in the area had affected the local worm population.
Armed with Geiger counters to assess radiation levels and equipped with personal protective gear to shield against radioactive particles, they collected worms from soil samples, decaying fruits, and various organic materials found within the exclusion zone.
Worms were gathered from various locations across the Chernobyl Exclusion Zone, exhibiting a range of radiation levels. These levels spanned from minimal radiation akin to that found in New York City to dangerously high radiation levels comparable to outer space, though the potential risk to the worms remained uncertain.
Following the field collection, the team transported the samples to Mousseau’s field laboratory located in a former residential building within Chernobyl. There, they meticulously extracted hundreds of nematodes from the soil and fruit samples. Subsequently, they relocated to a hotel in Kyiv, where they utilized travel microscopes to carefully isolate and establish cultures from each individual worm.
Upon returning to the laboratory at NYU, the researchers continued their investigation by subjecting the worms to freezing methods for further study.
“We can cryopreserve worms, and then thaw them for study later. That means that we can stop evolution from happening in the lab, something impossible with most other animal models, and very valuable when we want to compare animals that have experienced different evolutionary histories,” said Rockman.
Their investigation honed in on 15 worms belonging to the nematode species Oscheius tipulae, commonly utilized in genetic and evolutionary research. The team sequenced the genomes of these 15 O. tipulae worms collected from Chernobyl and juxtaposed them against the genomes of five O. tipulae specimens sourced from other global regions.
To their astonishment, despite employing various analytical methods, the researchers were unable to make out any discernible evidence of radiation-induced damage within the genomes of the Chernobyl-derived worms.
“This doesn’t mean that Chernobyl is safe—it more likely means that nematodes are really resilient animals and can withstand extreme conditions. We also don’t know how long each of the worms we collected was in the Zone, so we can’t be sure exactly what level of exposure each worm and its ancestors received over the past four decades,” noted Tintori.
Curious about whether the absence of a genetic signature was indicative of the worms in Chernobyl possessing exceptional DNA protection or repair mechanisms, the researchers devised a methodology to compare the growth rates of worm populations.
They then utilized this system to gauge the sensitivity of descendants from each of the 20 genetically distinct worms to various types of DNA damage.
The intriguing aspect of this study lies in the revelation that while different worm lineages exhibited varying degrees of DNA damage tolerance, these discrepancies did not align with the radiation levels at their respective collection sites. This implies that, contrary to popular belief that superheroes get their powers from radiation exposure, these worms did not become super worms from their exposure to radiation either.
Rather than suggesting that worms from Chernobyl have developed heightened radiation tolerance due to the radioactive environment, the findings indicate that these worms may not have undergone significant evolutionary adaptations in response to their surroundings.
These results provide researchers with valuable insight into the variability of DNA repair mechanisms among individuals. Despite the genetic simplicity of O. tipulae, these findings have the potential to enhance to enhance our understanding of natural variations in humans.
“Now that we know which strains of O. tipulae are more sensitive or more tolerant to DNA damage, we can use these strains to study why different individuals are more likely than others to suffer the effects of carcinogens,” said Tintori.
Cancer researchers are keenly interested in how various individuals within a species react to DNA damage. This inquiry is particularly pertinent as they strive to comprehend why certain humans, despite possessing a genetic predisposition to cancer, succumb to the disease while others do not.
“Thinking about how individuals respond differently to DNA-damaging agents in the environment is something that will help us have a clear vision of our own risk factors,” added Tintori.
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