Aside from being disconcertingly cute, tardigrades are also famous for the fact that they are nearly indestructible. These tiny creatures are extremophiles, adapted to live in environments that would kill most other organisms. Different species have different tolerances, but what is most interesting is the ability of some species to withstand large amounts of ionizing radiation. 1000 times more than the amount needed to kill a human.
Earlier this year, scientists looked at tardigrade species. Hypsibius exemplaris We want to understand how they can withstand such high doses of radiation. Surprisingly, they discovered that tardigrades had not evolved any way to protect their DNA from the damage caused by this radiation. Instead, they demonstrated a remarkable ability to repair that damage quickly and efficiently.
[Related: How super resilient tardigrades can fix their radiation-damaged DNA]
new studyA paper published October 24 in the journal Science examines the radiation resistance of another species of tardigrade. Hypsibius henanensis. (This is a new species discovered by the researchers themselves and named after China’s Henan province.) These tardigrades were exposed to large amounts of gamma rays (high-energy photons, a type of ionizing radiation), and the researchers We then studied how their systems reacted.
they found that out. H. henanensis It exhibits the same ability to repair damaged DNA. H. exepralisthere are some other tricks.
The danger that ionizing radiation poses to living organisms stems from its ability to ionize atoms. Gamma ray photons have enough energy that when they hit an atom, they essentially knock off one of the atom’s electrons. If that atom happened to be part of a DNA molecule, the result could be a break in one or both of the delicate strands that form the famous double helix. Breaks in both strands are particularly dangerous, as any damage can prevent the molecule from replicating properly. (This is how ionizing radiation causes cancer.)
when H. henanensis When exposed to radiation, three important mechanisms are activated. The first is the same turbocharged DNA repair ability. H. exepralis. This is driven by a protein called TRID1, which appears to be unique to tardigrades. The researchers behind the new study investigated exactly how TRID1 responds to radiation exposure. They found that it collects at sites where DNA has undergone double-strand breaks and promotes the accumulation of another protein called 53BPI. seems critical For repair of double-strand breaks.
The researchers also looked at genes that are activated in response to radiation exposure. This gene, BSC1, responds to radiation by upregulating the production of two proteins known to be important for mitochondrial ATP synthesis. the fact that H. henanensis produce them all at once In response to radiation exposure, researchers theorized that they may also play a role in DNA repair. This may also explain why radiation exposure in humans causes mitochondrial dysfunction. “Our study showed an unexpected link between mitochondrial proteins and nuclear DNA repair and provided a possible explanation for mitochondrial dysregulation after radiation exposure.”
H. henanensis It also appears to be able to minimize the amount of damage caused by ionizing radiation in the first place. Direct damage to DNA can be fatal, but ionizing radiation It can also cause damage in other ways. The paper explains:[Ionizing radiation] exerts its biological effects through two mechanisms: direct and indirect effects. The latter is mediated by reactive oxygen species (ROS) and accounts for 60% to 70%. [radiation’s] Impact of IR”
Life has its own defense system against free radicals in the form of antioxidants. These molecules react with free radicals and effectively neutralize them. There is generally a balance between both in living things. However, when there are too many free radicals in an organism’s system and its antioxidant capacity is overloaded, the organism experiences: “Oxidative stress”A state in which ROS molecules are free to react with cellular tissue, DNA molecules, and anything else that gets in the way.
H. henanensis deals with this problem by producing large amounts of proteins called betalains in response to radiation exposure. These proteins are highly effective antioxidants and essentially work to scavenge excess free radicals before they can wreak havoc on the tardigrade’s system. The presence of betalains in tardigrades is noteworthy because betalains are commonly found in plants. Its production is regulated by a gene called DODA1, and the researchers suspect that it reached the tardigrade via this gene. horizontal gene transferUnderstanding how tardigrades survive radiation exposure is not only interesting in itself, but could also help humans do the same. Earlier this year, inspired by research on H. exepralisresearchers discovered that TRID1 was introduced into human cells. Seems to increase a cell’s ability to resist DNA damage. Given that there is still much we don’t understand about the resilience of tardigrades, these humble little animals may still have many secrets to uncover. As the team behind this new paper stated in a statement“Extremophiles such as tardigrades” [are] A treasure trove of unexplored molecular mechanisms of stress tolerance. Functional studies on these radioresistance mechanisms…further expand our understanding of cell survival under extreme conditions and may provide inspiration for promoting human health and fighting disease. ”
