Mounting evidence in several organisms suggests that some epigenetic modifications acquired by an individual during its lifetime can be inherited for multiple future generations. This phenomenon, termed transgenerational epigenetic inheritance, may provide a mechanism for the inheritance of environmentally acquired traits. We are studying transgenerational epigenetic inheritance using a model organism, the nematode Caenorhabditis elegans.
We have developed a system in which RNAi-induced silencing of a GFP transgene is robustly inherited for multiple generations in the absence of the initial RNAi trigger. We show that the histone H3 lysine 9 (H3K9) trimethyltransferase SET-25 and the putative histone methyltransferase SET-32 are required for effective transmission of transgene silencing. However, the H3K9 mono and dimethyltransferase MET-2 is not required for transgene silencing inheritance. Specifically, we show that whilst set-25 and set-32 mutant animals exposed to RNAi display transgene silencing, their unexposed offspring fail to inherit silencing. Intriguingly, the few animals which escape this failure and remain silenced then produce subsequent generations of silenced progeny. This suggests that SET-25 and SET-32 are required for the establishment of a transgenerational silencing signal, but not for long-term maintenance of this signal between subsequent generations. To elucidate the mechanism of the establishment of heritable silencing, we aim to identify the binding partners of SET-25 and SET-32 during and immediately following RNAi exposure. We have used CRISPR-Cas9 genome editing to tag endogenous SET-25 and SET-32 with mCherry. We are performing co-immunoprecipitation experiments on the tagged proteins followed by mass spectrometry to identify the broader protein interaction network, and will report on these findings.