title: Ultraviolet B retards growth, induces oxidative stress, and modulates DNA repair-related gene and heat shock protein gene expression in the monogonont rotifer, Brachionus sp.
abstract: Ultraviolet B (UV-B) radiation causes direct cellular damage by breakage of DNA strands and oxidative stress induction in aquatic organisms. To understand the effect of UV-B radiation on the rotifer, Brachionus sp., several parameters including 24-h survival rate, population growth rate, and ROS level were measured after exposure to a wide range of UV-B doses. To check the expression of other important inducible genes such as replication protein A (RPA), DNA-dependent protein kinase (DNA-PK), Ku70, Ku80, and heat shock proteins (hsps) after UV-B radiation, we observed dose- and time-dependency at 2kJ/m(2). We also examined 13 hsp genes for their roles in the UV-B damaged rotifer. Results showed that UV-B remarkably inhibited the population growth of Brachionus sp. The level of intracellular reactive oxygen species (ROS) was high at 2kJ/m(2), suggesting that 2kJ/m(2) would already be toxic. This result was supported by other enzymatic activities, such as GSH levels, glutathione peroxidase, glutathione S-transferase, and glutathione reductase. For dose dependency, low doses of UV-B radiation (2, 4, and 6kJ/m(2)) significantly up-regulated the examined genes (e.g. RPA, DNA-PK, Ku70, and Ku80). For the time course study, RPA genes showed immediate up-regulation but returned to basal or lower expression levels compared to the control 3h after UV-B exposure. The DNA-PK and Ku70/80 genes significantly increased, indicating that they may be involved in repairing processes against a low dose of UV-B exposure (2kJ/m(2)). At the basal level, the hsp90α1 gene showed the highest expression, and followed by hsp10, hsp30, hsp60, and hsc70, and hsp90β in adults (w/o egg). In eggs, the hsp10 gene was expressed the highest, and followed by hsp30, hsp27, hsp90α1, and hsp60 genes. In real-time RT-PCR array on rotifer hsp genes, low doses of UV-B radiation (2 and 4kJ/m(2)) showed up-regulation of several hsp genes but most of the hsp genes showed down-regulation at 8kJ/m(2) and higher, indicating that significant Hsp-mediated cellular damage already occurred at low doses. For the time course study of four hsp genes (hsp20, hsp27, hsp70, hsp90α1), they showed a significant correlation for UV-B radiation (2kJ/m(2)). In this paper, we demonstrated that UV-B radiation would affect growth retardation with up- or down-regulation of some important genes in DNA replication, repair process, and chaperoning. This finding provides a better understanding of molecular mechanisms involved in UV-B-mediated cellular damage in the rotifer, Brachionus sp.
authors.affiliation: Department of Chemistry, and Research Institute for Natural Sciences, College of Natural Sciences, Hanyang University, Seoul, South Korea.
authors.forename: Ryeo-Ok
authors.initials: RO
authors.lastname: Kim
authors.forename: Jae-Sung
authors.initials: JS
authors.lastname: Rhee
authors.forename: Eun-Ji
authors.initials: EJ
authors.lastname: Won
authors.forename: Kyun-Woo
authors.initials: KW
authors.lastname: Lee
authors.forename: Chang-Mo
authors.initials: CM
authors.lastname: Kang
authors.forename: Young-Mi
authors.initials: YM
authors.lastname: Lee
authors.forename: Jae-Seong
authors.initials: JS
authors.lastname: Lee
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D017931:DNA Primers / Q000235:genetics; D004260:DNA Repair / Q000235:genetics; D051747:DNA-Activated Protein Kinase / Q000378:metabolism; D005786:Gene Expression Regulation / Q000528:radiation effects*; D006360:Heat-Shock Proteins / Q000235:genetics; D018384:Oxidative Stress / Q000528:radiation effects*; D017382:Reactive Oxygen Species / Q000378:metabolism; D051716:Replication Protein A / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012403:Rotifera / Q000235:genetics / Q000254:growth & development / Q000378:metabolism / Q000528:radiation effects*; D014466:Ultraviolet Rays
chemical_list: D017931:DNA Primers; D006360:Heat-Shock Proteins; D017382:Reactive Oxygen Species; D051716:Replication Protein A; D051747:DNA-Activated Protein Kinase