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1. The tardigrade Hypsibius exemplaris dramatically upregulates DNA repair pathway genes in response to ionizing radiation

   https://doi.org/10.1016/j.cub.2024.03.019  

   Clark-Hachtel, Courtney M.; Hibshman, Jonathan D.; De Buysscher, Tristan; Stair, Evan R.; Hicks, Leslie M.; Goldstein, Bob (May 2024, Current Biology)

   Tardigrades can survive remarkable doses of ionizing radiation, up to about 1,000 times the lethal dose for humans. How they do so is incompletely understood. We found that the tardigrade Hypsibius exemplaris suffers DNA damage upon gamma irradiation, but the damage is repaired. We show that this species has a specific and robust response to ionizing radiation: irradiation induces a rapid upregulation of many DNA repair genes. This upregulation is unexpectedly extreme—making some DNA repair transcripts among the most abundant transcripts in the animal. By expressing tardigrade genes in bacteria, we validate that increased expression of some repair genes can suffice to increase radiation tolerance. We show that at least one such gene is important in vivo for tardigrade radiation tolerance. We hypothesize that the tardigrades’ ability to sense ionizing radiation and massively upregulate specific DNA repair pathway genes may represent an evolved solution for maintaining DNA integrity. 

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2. Atomic autoionization in the photo-dissociation of super-excited deuterated water molecules fragmenting into D ⁺ + O ⁺ + D

   https://doi.org/10.1039/D3CP02438E  

   Iskandar, W; Rescigno, T N; Orel, A E; Larsen, K A; Griffin, B; Call, D; Davis, V; Jochim, B; Severt, T; Williams, J B; et al (August 2023, Physical Chemistry Chemical Physics)

   Creation of a super-excited radical water cation results in a long-lived excited oxygen fragment that can act as a destructive carrier and initiate secondary reactions such as breakup of DNA strands – a key radiation damage mechanism. 

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3. Ultrafast Processes Occurring in Radiolysis of Highly Concentrated Solutions of Nucleosides/Tides

   https://doi.org/10.3390/ijms20194963  

   MA, Jun; Denisov, Sergey A.; Adhikary, Amitava; Mostafavi, Mehran (October 2019, International Journal of Molecular Sciences)

   null (Ed.)

   Among the radicals (hydroxyl radical (•OH), hydrogen atom (H•), and solvated electron (esol−)) that are generated via water radiolysis, •OH has been shown to be the main transient species responsible for radiation damage to DNA via the indirect effect. Reactions of these radicals with DNA-model systems (bases, nucleosides, nucleotides, polynucleotides of defined sequences, single stranded (ss) and double stranded (ds) highly polymeric DNA, nucleohistones) were extensively investigated. The timescale of the reactions of these radicals with DNA-models range from nanoseconds (ns) to microseconds (µs) at ambient temperature and are controlled by diffusion or activation. However, those studies carried out in dilute solutions that model radiation damage to DNA via indirect action do not turn out to be valid in dense biological medium, where solute and water molecules are in close contact (e.g., in cellular environment). In that case, the initial species formed from water radiolysis are two radicals that are ultrashort-lived and charged: the water cation radical (H2O•+) and prethermalized electron. These species are captured by target biomolecules (e.g., DNA, proteins, etc.) in competition with their inherent pathways of proton transfer and relaxation occurring in less than 1 picosecond. In addition, the direct-type effects of radiation, i.e., ionization of macromolecule plus excitations proximate to ionizations, become important. The holes (i.e., unpaired spin or cation radical sites) created by ionization undergo fast spin transfer across DNA subunits. The exploration of the above-mentioned ultrafast processes is crucial to elucidate our understanding of the mechanisms that are involved in causing DNA damage via direct-type effects of radiation. Only recently, investigations of these ultrafast processes have been attempted by studying concentrated solutions of nucleosides/tides under ambient conditions. Recent advancements of laser-driven picosecond electron accelerators have provided an opportunity to address some long-term puzzling questions in the context of direct-type and indirect effects of DNA damage. In this review, we have presented key findings that are important to elucidate mechanisms of complex processes including excess electron-mediated bond breakage and hole transfer, occurring at the single nucleoside/tide level. 

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4. Chromosomes remain individualized through interphase in embryos of the tardigrade Hypsibius exemplaris

   https://doi.org/10.1091/mbc.E25-07-0356  

   Papell, Lillian D; Coke, Adriana N; de_Jesus, Bailey N; Harry, Clayton J; Zhang, Pu; Goldstein, Bob (January 2026, Molecular Biology of the Cell)

   Onishi, Masayuki (Ed.)

   Tardigrades are microscopic animals that can survive exceptional levels of ionizing radiation or desiccation—DNA-damaging conditions that would kill most animals. Irradiation or radiomimetic drug treatment of the tardigrade Hypsibius exemplaris can induce remarkably high expression levels of DNA repair genes, primarily those in the base excision repair and nonhomologous end joining pathways. How tardigrades can repair widespread DNA damage without producing frequent, large-scale chromosome structural abnormalities, like chromosome translocations and fusions, is unknown. Here, we report the results of examining chromosome and nuclear architecture throughout the cell cycle in early embryos of H. exemplaris. We found that H. exemplaris chromosomes are maintained in an individualized form throughout the cell cycle. We were surprised to also find that each chromosome is housed in a fully or partially separate lamin-lined compartment, instead of all chromosomes being housed in a single, nearly spherical nuclear lamina and envelope. Our results reveal unusual chromosomal and nuclear organization in a tardigrade. We speculate that these unexpected features might limit chromosomal rearrangements during DNA damage repair in extreme conditions. 

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5. Sunburned plankton: ultraviolet radiation inhibition of phytoplankton photosynthesis in the Community Earth System Model version 2

   https://doi.org/10.5194/gmd-18-8217-2025  

   Coupe, Joshua; Lovenduski, Nicole S; Gleason, Luise S; Levy, Michael N; Krumhardt, Kristen; Lindsay, Keith; Bardeen, Charles; Tabor, Clay; Harrison, Cheryl; MacLeod, Kenneth G; et al (January 2025, Geoscientific Model Development)

   Ultraviolet (UV) radiation can damage DNA and kill cells. We use laboratory and observational studies of the harmful effect of UV radiation on marine photosynthesizers to inform the implementation of a UV radiation damage function for phytoplankton photosynthesis in a modified version of the Community Earth System Model version 2 (CESM2-UVphyto). CESM2-UVphyto is capable of simulating UV inhibition of photosynthesis among modeled phytoplankton and ocean column penetration of UV-A, UV-B, and UV-C radiation. We conduct a series of simulations with CESM2-UVphyto using the Marine Biogeochemistry Library (MARBL) ecosystem model to understand the sensitivity of phytoplankton productivity to UV radiation. Results from the simulations indicate that increased UV radiation shifts the vertical distribution of phytoplankton biomass and productivity deeper into the column, causes a moderate decline in total global productivity, and changes phytoplankton community structure. Our new CESM2-UVphyto model configuration can be used to quantify the potential ocean biogeochemical and ecosystem impacts resulting from events that disturb the stratospheric ozone layer, such as an asteroid impact, a volcanic eruption, a nuclear war, and stratospheric-aerosol-injection-based geoengineering. 

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