Potential radiosensitive germline biomarkers in the testes of wild mice after the Fukushima accident

Abstract

We investigated potential germline-specific radiosensitive biomarkers in the testes of large Japanese field mice (Apodemus speciosus) exposed to low-dose-rate (LDR) radiation after the Fukushima accident. Fukushima wild mice testes were analysed via RNA-sequencing to identify genes differentially expressed in the breeding and non-breeding seasons when compared to controls. Results revealed significant changes during the breeding season, with Lsp1 showing a considerable upregulation, while Ptprk and Tspear exhibited significant reductions. Conversely, in the non-breeding season, Fmo2 and Fmo2 (highly similar) were significantly upregulated in radiation-exposed Fukushima mice. qPCR analysis results were consistent with transcriptome sequencing, detecting Lsp1 and Ptprk regulation in the testes of Fukushima mice. While differences in gene expression were observed, these do not imply any causal association between the identified biomarkers and chronic LDR exposure, as other factors such as the environment and developmental age may contribute. This study provides valuable insights into the reproductive biology is affected by environmental radiation and highlights the value of assessing the effects of chronic LDR radiation exposure on testicular health in wild mice.

Keywords: Apodemus speciosus; Fukushima accident; low‐dose‐rate radiation; radiosensitive biomarkers.

Fig. 1

Sampling locations included a control site in Niigata Prefecture, Japan, as well as three areas in Fukushima Prefecture, Japan, that were affected by radioactive contamination. Testes were sampled from large Japanese field mice at all locations, during both the breeding and non‐breeding seasons. The blue circle indicates a large Japanese field mice sampling point in Niigata. The red circles indicate sampling points in areas that were considered evacuation zones. Spatial data were obtained from the National Land Numerical Information download service (http://nlftp.mlit.go.jp/ksj/index.html). Scale bar = 10 mm.

Fig. 2

DEGs between in the testis of large Japanese field mice in the breeding versus non‐breeding season. (A) Venn diagram of gene expression. The figure shows genes expressed only in the breeding season (red circle) and the non‐breeding (blue circle), with the overlapping part of the circle representing genes overlapping between the groups. The degree of similarity in gene expression between samples was visualised in hierarchical clustering (B) and principal component analysis (C).

Fig. 3

Pairwise scatter plot and testicular gene expression heatmap comparing the testes sampled from contaminated and control groups. (A) Pairwise scatter plot of DEGs between Fukushima and control groups. (B) Heatmap of DEGs. Yellow represents high‐expression genes, and purple represents low‐expression genes.

Fig. 4

Significant gene expression changes in the testes of contaminated and control mice sampled during the breeding season. (A) Volcano plot of differential gene expression patterns. (B) Bar plots of significantly altered gene expression ratio in the testes. No. of wild mice used for breeding season testes of contaminated (n = 3) and control (n = 3). All data are expressed in relative units. Statistical analysis was performed using edger (Version 3.42.4) using TMM‐normalised values. Data are presented as mean ± SE. Arhgap28, rho GTPase‐activating protein 28; C1qtnf1, C1q and tumour necrosis factor‐related protein 1; Lsp1, lymphocyte specific 1; Mapre2, microtubule‐associated protein RP/EB family member 2; Pmel, premelanosome protein; Ptprk, protein tyrosine phosphatase receptor type K; RP23‐220C16, Mus musculus BAC clone RP23‐220C16 from 8; Tspear, thrombospondin type laminin G domain and EAR repeats; Umodl1, uromodulin‐like 1.

Fig. 5

Significant gene expression changes in the non‐breeding season testes of contaminated and control mice. (A) Volcano plot of the differential gene expression patterns. (B) Bar plots of significantly altered gene expression ratio in the testes. No. of wild mice used for non‐breeding season testes of contaminated (n = 3) and control (n = 3). All data are expressed in relative units. Statistical analysis was performed using edger (Version 3.42.4) using TMM‐normalised values. Data are presented as mean ± SE. Fmo2 HS, flavin‐containing monooxygenase 2 highly similar; Fmo2, flavin‐containing monooxygenase 2.

Fig. 6

qPCR detection of potential biomarkers Lsp1, Ptprk, Tspear, Fmo2, and Fmo2 HS in the testis of large Japanese field mice. Fmo2 HS, flavin‐containing monooxygenase 2 highly similar; Fmo2, flavin‐containing monooxygenase 2; Lsp1, lymphocyte specific 1; Ptprk, protein tyrosine phosphatase receptor type K; Tspear, thrombospondin type laminin G domain and EAR repeats. No. of wild mice used for Niigata (n = 4), Tanashio (n = 5), Ide (n = 3), Akogi (n = 4), and Omaru (n = 3). Statistically significant differences were evaluated using Dunnett's test. *represents the significance of difference (P < 0.05).