Project description:Life experiences trigger transgenerational small RNA-based responses in C. elegans nematodes1. Dedicated machinery ensures that heritable effects would re-set, typically after a few generations2,3. Here we show that isogenic individuals differ dramatically in the persistence of transgenerational responses. By examining lineages composed of >20,000 worms we reveal 3 inheritance rules: (1) Once a response is initiated, each isogenic mother stochastically assumes an “inheritance state”, establishing a commitment that determines the fate of the inheritance. (2) The response that each mother transfers is uniform in each generation of her descendants. (3) The likelihood that an RNAi response would transmit to the progeny increases the more generations the response lasts, according to a “hot hand” principle. Mechanistically, the different parental “inheritance states” correspond to global changes in the expression levels of endogenous small RNAs, immune response genes, and targets of the conserved transcription factor HSF-1. We show that these rules predict the descendants’ developmental rate and resistance to stress.
Project description:Some epigenetic modifications are inherited from one generation to the next, providing a potential mechanism for the inheritance of environmentally acquired traits. Transgenerational inheritance of RNA interference phenotypes in C. elegans provides an excellent model to study this phenomenon, and whilst studies have implicated both chromatin modifications and small RNA pathways in heritable silencing their relative contributions remain unclear. Here we demonstrate that the histone methyltransferases 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 suggesting that transgenerational epigenetic inheritance is a multi-step process, with distinct genetic requirements for establishment and maintenance of heritable silencing. Furthermore, small RNA sequencing reveals that the abundance of secondary siRNA (thought to be the effector molecules of heritable silencing) does not correlate with silencing phenotypes. Together, our results suggest that the current mechanistic models of epigenetic inheritance are incomplete.
