Abstract
Studies of the biological effects of low-level and below-background radiation are important in understanding the potential effects of radiation exposure in humans. To study this issue we exposed the nematode Caenorhabditis elegans to average background and below-background radiation levels. Two experiments were carried-out in the underground radiation biology laboratory at the Waste Isolation Pilot Plant (WIPP) in New Mexico USA. The first experiment used naïve nematodes with data collected within 1 week of being placed underground. The second experiment used worms that were incubated for 8 months underground at below background radiation levels. Nematode eggs were placed in two incubators, one at low radiation (ca.15.6 nGy/hr) and one supplemented with 2 kg of natural KCl (ca. 67.4 nGy/hr). Phenotypic variables measured were: (1) egg hatching success (2) body size from larval development to adulthood, (3) developmental time from egg to egg laying adult, and (4) egg laying rate of young adult worms. Transcriptome analysis was performed on the first experiment on 72 h old adult worms. Within 72 h of being underground, there was a trend of increased egg-laying rate in the below-background radiation treatment. This trend became statistically significant in the group of worms exposed to below-background radiation for 8 months. Worms raised for 8 months in these shielded conditions also had significantly faster growth rates during larval development. Transcriptome analyses of 72-h old naïve nematode RNA showed significant differential expression of genes coding for sperm-related proteins and collagen production. In the below-background radiation group, the genes for major sperm protein (msp, 42% of total genes) and sperm-related proteins (7.5%) represented 49.5% of the total genes significantly up-regulated, while the majority of down-regulated genes were collagen (col, 37%) or cuticle-related (28%) genes. RT-qPCR analysis of target genes confirmed transcriptomic data. These results demonstrate that exposure to below-background radiation rapidly induces phenotypic and transcriptomic changes in C. elegans within 72 h of being brought underground.
Highlights
Life on earth has evolved with a constant exposure to ionizing radiation [1, 2]
Such studies typically expose a control group to normal background radiation levels and compare this group to a group that is exposed to a group slightly higher radiation levels [41]
In this study the effects of levels of a radiation exposure that was around 1/3 of normal background was compared to a group kept at normal background radiation levels
Summary
Life on earth has evolved with a constant exposure to ionizing radiation [1, 2]. While all organisms are continuously exposed to ionizing radiation, natural rates of exposure can vary widely. Pioneering experiments examining effects of below-normal background radiation levels demonstrated that cultures of Paramecium tetraurelia grown at 11.4 nGy hr−1 had a reduced grow rate and longer generation time, compared to control cultures grown at 199 nGy hr−1 [14]. In similar experiments Satta et al reported that Saccharomyces cerevisiae cells grown at 4.5 nGy hr−1 exhibited a higher frequency of DNA damage when exposed to the genotoxin methyl-methane sulfonate compared to cultures grown at background levels [15]. They found numerous biological differences between the hamster tissue cell cultures grown at 4.5 nGy hr and normal background radiation levels. We compared basic life-history and gene expression patterns between these two groups to document if these low radiation levels induced any biological response
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