GSE211846
Chromatin epimutations in transgenerational epigenetic inheritance
Epigenetic inheritance is the transmission of altered gene expression states across dividing cells without DNA sequence variation. Induced epigenetic changes (epimutations) have been extensively studied, but importantly, epimutations also occur spontaneously in a manner reminiscent of DNA sequence change. Small RNAs are established as a source of spontaneous epimutations which transmit gene expression changes over multiple generations in C.elegans. These changes are generally short lived, but rarely long-lived changes occur. Given that chromatin state is a critical regulator of gene expression, we explored whether chromatin states also undergo spontaneous change and whether this could be a potential alternative mechanism for transgenerational epigenetic inheritance.  We compared the chromatin profiles and gene expression profiles at matched time points from a twenty generation bottlenecked lineage of C.elegans. We found that heritable changes in gene expression arose at a higher rate than the estimate for DNA sequence variation, indicating that these were true epigenetic events. In addition to recapitulating the known role for small RNAs, we provide evidence for chromatin mediated epimutations as an alternative mechanism driving epigenetic inheritance. Chromatin epimutations were heritable, enriched in the germline and synchronised with inherited gene expression changes. As with small RNA mediated epimutations, they were generally short lived with a tendency to resolve to baseline after 2-3 generations. A subset of chromatin epimutations however were long lasting, and these were uniquely enriched in piRNA clusters. Genes with long lived epimutations were implicated in multiple components of xenobiotic response pathways. This points to a mechanism for epigenetic 'anticipation' of environmental stressors.  Adaptive traits driven by epimutations may be selected for under adverse conditions and lost on return to normal conditions, enabling soft adaptation in the absence of genetic sequence change. Overall design: Examination of time matched RNA, ATAC and small RNA from 10 time points across 3 independent lineages of C.elegans