title: Analysis of DNA repair and protection in the Tardigrade Ramazzottius varieornatus and Hypsibius dujardini after exposure to UVC radiation.
abstract: Tardigrades inhabiting terrestrial environments exhibit extraordinary resistance to ionizing radiation and UV radiation although little is known about the mechanisms underlying the resistance. We found that the terrestrial tardigrade Ramazzottius varieornatus is able to tolerate massive doses of UVC irradiation by both being protected from forming UVC-induced thymine dimers in DNA in a desiccated, anhydrobiotic state as well as repairing the dimers that do form in the hydrated animals. In R. varieornatus accumulation of thymine dimers in DNA induced by irradiation with 2.5 kJ/m(2) of UVC radiation disappeared 18 h after the exposure when the animals were exposed to fluorescent light but not in the dark. Much higher UV radiation tolerance was observed in desiccated anhydrobiotic R. varieornatus compared to hydrated specimens of this species. On the other hand, the freshwater tardigrade species Hypsibius dujardini that was used as control, showed much weaker tolerance to UVC radiation than R. varieornatus, and it did not contain a putative phrA gene sequence. The anhydrobiotes of R. varieornatus accumulated much less UVC-induced thymine dimers in DNA than hydrated one. It suggests that anhydrobiosis efficiently avoids DNA damage accumulation in R. varieornatus and confers better UV radiation tolerance on this species. Thus we propose that UV radiation tolerance in tardigrades is due to the both high capacities of DNA damage repair and DNA protection, a two-pronged survival strategy.
authors.affiliation: Biospheric Science Branch, NASA Ames Research Center, Moffett Field, California, United States of America. horikawadd@gmail.com
authors.forename: Daiki D
authors.initials: DD
authors.lastname: Horikawa
authors.forename: John
authors.initials: J
authors.lastname: Cumbers
authors.forename: Iori
authors.initials: I
authors.lastname: Sakakibara
authors.forename: Dana
authors.initials: D
authors.lastname: Rogoff
authors.forename: Stefan
authors.initials: S
authors.lastname: Leuko
authors.forename: Raechel
authors.initials: R
authors.lastname: Harnoto
authors.forename: Kazuharu
authors.initials: K
authors.lastname: Arakawa
authors.forename: Toshiaki
authors.initials: T
authors.lastname: Katayama
authors.forename: Takekazu
authors.initials: T
authors.lastname: Kunieda
authors.forename: Atsushi
authors.initials: A
authors.lastname: Toyoda
authors.forename: Asao
authors.initials: A
authors.lastname: Fujiyama
authors.forename: Lynn J
authors.initials: LJ
authors.lastname: Rothschild
mesh_terms: D000222:Adaptation, Physiological / Q000235:genetics*; D000818:Animals; D004249:DNA Damage; D004260:DNA Repair / Q000528:radiation effects*; D003890:Desiccation; D004307:Dose-Response Relationship, Radiation; D011740:Pyrimidine Dimers / Q000235:genetics* / Q000378:metabolism; D011836:Radiation Tolerance / Q000235:genetics*; D058467:Tardigrada / Q000235:genetics / Q000528:radiation effects*; D014466:Ultraviolet Rays; D014867:Water / Q000378:metabolism
chemical_list: D011740:Pyrimidine Dimers; D014867:Water