Abstract
Altered copy number of certain highly repetitive regions of the genome, such as satellite DNA within heterochromatin and ribosomal RNA loci (rDNA), is hypothesized to help safeguard the genome against damage derived from external stressors. We quantified copy number of the 18S rDNA and a pericentromeric satellite DNA (Msat‐160) in bank voles (Myodes glareolus) inhabiting the Chernobyl Exclusion Zone (CEZ), an area that is contaminated by radionuclides and where organisms are exposed to elevated levels of ionizing radiation. We found a significant increase in 18S rDNA and Msat‐160 content in the genomes of bank voles from contaminated locations within the CEZ compared with animals from uncontaminated locations. Moreover, 18S rDNA and Msat‐160 copy number were positively correlated in the genomes of bank voles from uncontaminated, but not in the genomes of animals inhabiting contaminated, areas. These results show the capacity for local‐scale geographic variation in genome architecture and are consistent with the genomic safeguard hypothesis. Disruption of cellular processes related to genomic stability appears to be a hallmark effect in bank voles inhabiting areas contaminated by radionuclides.
Highlights
Release of pollutants into the environment has diverse impacts upon wildlife, such as the bank vole (Myodes glareolus) (Figure 1) and the ecosystems they inhabit (Acevedo-Whitehouse & Duffus, 2009; Isaksson, 2010)
We used quantitative PCR to quantify the relative amounts of (a) 18S ribosomal DNA (rDNA) and (b) Msat-160 as proxies for heterochromatin content in genomes of bank voles that have inhabited areas contaminated with radionuclides for estimated 50 generations (Baker et al, 2017)
The correlation between rDNA and Msat-160 copy number in bank voles from uncontaminated areas within and outside the Chernobyl Exclusion Zone (CEZ), but not in animals from contaminated areas, implies some disruption to typical genome architecture when animals are exposed to environmental radionuclides
Summary
Release of pollutants into the environment has diverse impacts upon wildlife, such as the bank vole (Myodes glareolus) (Figure 1) and the ecosystems they inhabit (Acevedo-Whitehouse & Duffus, 2009; Isaksson, 2010). The hypothesized role of heterochromatin in helping to safeguard the genome against IR-induced damage (Qiu, 2015) is derived from the tendency for heterochromatin to localize at the nuclear periphery where it forms a three-dimensional structure that physically surrounds the actively transcribed euchromatic regions (Geyer et al, 2011), possibly protecting these territories from impacts of IR and oxygen radicals This “safeguard hypothesis” is supported by studies that demonstrate relationship between sensitivity to radiation, other mutagens or aging and loss in repetitive content such as telomeres (Goytisolo et al, 2000; Zhang et al, 2016), ribosomal DNA (rDNA) (Ide et al, 2010; Kobayashi, 2011, 2014), and heterochromatin in general (Larson et al, 2012; Yan et al, 2011). We used quantitative PCR (qPCR) to quantify the relative amounts of (a) 18S rDNA and (b) Msat-160 (a pericentromeric satellite sequence) as proxies for heterochromatin content in genomes of bank voles that have inhabited areas contaminated with radionuclides for estimated 50 generations (Baker et al, 2017)
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