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EFFECTS OF LOW-DOSE GAMMA IRRADIATION DURING EARLY LIFE
STAGES IN THE ZEBRAFISH MODEL
ab
Selma Hurem , Hans Christian Teienac, Ole Christian Lindac, Dag Anders Bredeac,
Turid Hertel-Aasac, Lene Sørlie Heierac, Vidar Bergab, Leonardo Martinab, Deborah
Oughtonac, Brit Salbuac, Peter Alestrømab, Jan Ludvig Lycheab
a
Centre for Environmental Radioactivity (CERAD CoE), Norway
b
Norwegian University of Life Sciences, Vetbio, Campus Oslo, Norway
c
Norwegian University of Life Sciences, Department of Environmental Sciences,
Campus Ås, Norway
Human and zebrafish genome share 70% of the genes. The aim of this study was to
assess phenotypic and genotypic changes in zebrafish embryos after exposure to low
dose and chronic dose-rates of γ-radiation during two sensitive developmental stages.
Zebrafish embryos AB wild type were exposed to dose-rates ranging from 0.5 to 40
mGy/h external 60Co gamma irradiation for a period of 3 hours (hpf) and 5 days post
fertilization (dpf), for a total of 118 hours. Samples for gene expression analysis were
collected at 5.5 hpf. Mortality, malformations, and the hatching rate were observed at 48
and 118 hpf. Total RNA for gene transcription analysis was isolated from embryos
exposed between 2.5 hours and 5.5 hpf which are across the mid blastula transition and
early gastrula stage of development. The quality of RNA sequenced samples was
determined by photometric parameters (260/280>1.8, 260/230>2, yield>200ng/µl) and
RNA integrity number (RIN>8.5) (Bioanalyzer; Agilent technologies, USA). The RNA
was sequenced at BGI Tech Solutions Co., Ltd., Hong Kong. Embryo hatching rate and
number of malformations were significantly different from controls in all exposure
groups. Mortality observed at 5dpf was higher than in controls for all groups except for
the lowest dose-rate (0.5 mGy/h). This suggests that γ-radiation in the range of 1mGy/h
and higher during embryogenesis and early larval stage (equivalent to total doses of ca.
100 mGy or higher) induces acute toxic effects in zebrafish. Bioinformatic analysis of
RNA-seq data showed a clear dose response relationship between the number of
differentially regulated genes compared to controls, which increased with the γradiation dose. Analyzes of the gene expression data sets using Ingenuity Pathway
Analysis (IPA) showed significant changes in gene networks around hnf4α (hepatocyte
nuclear factor 4α) and cebpa (CCAAT/enhancer binding protein) and genes involved in
eif2 signaling. Interestingly, corresponding gene transcription changes were also found
in cancer patients in the post-Chernobyl period suggesting that the same mechanisms
are involved in humans and zebrafish exposed to ionizing radiation.