Periodic Reporting for period 4 - RNAEPIGEN (Mechanisms of epigenetic inheritance by short RNAs) Reporting period: 2020-08-01 to 2021-07-31 Summary of the context and overall objectives of the project Epigenetic mechanisms are considered to be central to the development of multicellular organisms made of different cell types, all having identical genomes. Similarly, they may explain how genetically identical organisms are capable of adapting to distinct environmental conditions. Yet, the molecular mechanisms regulating how epigenetic traits can be inherited during cell division or across generations are not fully understood. Using the nematode Caenorhabditis elegans, we have recently revealed how the nuclear Argonaute protein CSR-1 and its associated short RNAs participate in global transcriptional regulationand chromatin organization. This unprecedented observation opened up a new class of molecular mechanisms by which Argonaute proteins and their bound short RNAs may actively contribute to epigenetic inheritance in animals. This research proposal focuses on the characterization of short-RNA-based mechanisms of epigenetic inheritance during animal development and upon environmental changes. Using C. elegans as an animal model system, we plan to integrate genetic, biochemical, and molecular biology tools with high-throughput genomic and proteomic approaches to dissect (i) the molecular mechanism by which CSR-1-bound short RNAs regulate transcription, (ii) test their ability in propagating the memory of actively transcribed genomic regions during early embryonic development, and (iii) characterize their role in propagating the memory of stress responses across generations to facilitate the adaptation of animals to environmental changes.Given the association of nuclear Argonaute proteins with transcriptionally active loci in metazoans, we anticipate that similar CSR-1-like epigenetic functions are also conserved in humans. Therefore, our research has the potential to significantly advance our understanding of the molecular mechanisms underlying epigenetic inheritance and reveals their impact on animal development and adaptation to changing environment. Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far We are dissecting the mechanism by which nuclear Argonaute proteins regulate transcriptional programs during germline development and we achieved to identify an interesting connection between Argonaute proteins that promote transcription and Argonaute proteins that act as repressors. We are also characterizing how small RNAs regulate embryonic development and zygotic transcription. Finally, we have identified a novel function of a class of small RNAs, called piRNAs, in regulating endogenous transcriptional programs essential for gamete differentiation and functions. Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far) We have identified new potential mechanisms of Argonaute-mediated post-transcriptional regulation of mRNAs delivered to oocytes. Also, we identified the role of piRNAs in promoting transgenerational fertility in isogenic population of worms and in regulating endogenous transcriptional programs essential for animal fertility.
