The gene-expression analysis of transgenerational instability in mice

Transgenerational instability is characterized by genome-wide increases in mutation rates observed in the somatic and germline tissues of non-exposed offspring of irradiated parents. An increasing body of experimental evidence from animal studies suggests that the phenomenon of transgenerational instability is attributed to the yet unknown epigenetic changes induced in the germline of irradiated animals and manifested in their offspring. To establish whether paternal irradiation could result in the transgenerational changes in gene expression, CBA/Ca and BALB/c male mice were given 1 Gy of acute X-rays and mated 10 weeks after exposure to control females from the same strain. RNA samples were extracted from kidney, liver, spleen and brain of the first-generation offspring of irradiated and control parents. They were hybridised to the NimbleGen 12x135K multiplex expression array, containing 135,054 features on the expression profiles and covering 42,575 known mouse transcripts. Highly significant changes in gene expression at the FDR < 0.05 were detected in 39 transcripts, showing the same pattern in all four tissues. The GO analysis revealed three overlapping pathways showing highly significant enrichment (P < 10[superscript -6]) – rhythmic process, circadian rhythm and DNA-dependent regulation of transcription. Differentially expressed genes of interest were further validated by qPCR. The pattern of DNA methylation of a number of genes was established by single-molecule and conventional bisulfite sequencing. Paternal irradiation caused no differences in DNA methylation of the genes analysed. Methylation can be transmissible through many cell divisions, however, the transcripts and size of expression change varied between tissue-types suggesting a more permissive/modifiable epigenetic alteration including, perhaps, the histone code.