Elucidate how small RNAs and histone modifications regulate the inheritance of developmental programs
In C. elegans, the exposure to dsRNA induces the production of small RNAs that repress transcription on complementary genomic targets (1-3). These targets accumulate histone modifications associated with silencing, such as H3K9me3 and H3K27me3, which can be maintained for multiple generations, in absence of the initial dsRNA trigger (2,3). Similar to ectopic dsRNA, endogenous piRNAs can trigger the multigenerational transcriptional silencing of a single-copy transgene (4,5). Genetic approaches have revealed crosstalk between nuclear small RNA pathways and histone modifications, but the molecular mechanisms have not been elucidated. Moreover, the function of piRNA silencing in endogenous gene regulation, beyond transposon and transgene silencing, remain largely unexplored (6).
Our preliminary results show that small RNAs can actually target and silence the transcription of thousands of endogenous germline genes. This is happening in a very specific developmental time point during spermatogenesis. The activation and repression of Spermatogenic genes is a dynamic process, they are in fact only activated for few hours in adult worms and then are rapidly repressed and inherited in a silent state for the rest of the life cycle. Based on this new paradigm of endogenous gene silencing by small RNAs, we are proposing to characterize the small RNA-induced silencing complexes -using several proteomic approaches.
We will elucidate, the complexes that work in the initiation of the silencing and those that are required for the maintenance and inheritance of the silencing in the next generation. Our results will not only reveal the steps by which small RNAs induce chromatin silencing, but also, will show how these epigenetic inheritance mechanisms work endogenously to regulate the inheritance of global transcriptional programs during animal development and upon environmental stresses.
1. Guang, S. et al. Nature (2010). doi:10.1038/nature09095
2. Gu, S. G. et al. Nat. Genet. (2012). doi:10.1038/ng.1039
3. Mao, H. et al. Curr. Biol. (2015). doi:10.1016/j.cub.2015.07.051
4. Shirayama, M. et al. Cell (2012). doi:10.1016/j.cell.2012.06.015
5. Ashe, A. et al. Cell (2012). doi:10.1016/j.cell.2012.06.018
6. Rechavi, O. & Lev, I. Curr. Biol. 27, 720–730 (2017).