We wish to understand the regulation and function of H3K23me3, an understudied histone modification that is conserved across the eukaryotic domain. The germline nuclear RNAi pathway in C. elegans has been used as a powerful paradigm to uncover novel mechanisms of transgenerational epigenetic inheritance. We recently discovered that nuclear RNAi induces H3K23me3, in addition to the well-known H3K9me3 and H3K27me3, at target genes. The H3K23me3 mark is deposited by histone methyltransferase SET-32 [1]. Absence of SET-32, but not the H3K9 HMTs (MET-2 and SET-25), is linked to a defect in transgenerational establishment of heritable gene silencing [2,3]. We found that
set-32 single mutation does not fully abolish H3K23me3, indicating the existence of additional H3K23 HMT(s) [1]. In this study, we took a combined approach of genetics, biochemical and genomic experimentation to identify additional H3K23 HMTs. So far, we have collected RNA-seq, sRNA-seq, and ChIP-seq data and performed initial transgenerational phenotypic analysis for some mutant animals. To date, we have found a putative H3K23 HMT, which together with SET-32, is required for nuclear RNAi and robust germline development at the restrictive temperature. Both whole-genome and phenotypic analyses for the putative H3K23 HMT will be presented at the conference. Currently, we are investigating why H3K23me3 is needed for nuclear RNAi by examining its roles in regulating other components of the pathway, including siRNA and other histone modifications. We hope these results will help us achieve the long-term goal of understanding the channels and barriers of epigenetic inheritance. [1] Schwartz-Orbach, L., Zhang, C., Sidoli, S., Amin, R., Kaur, D., Zhebrun, A., Ni, J., & Gu, S. G. (2020). Caenorhabditis elegans nuclear RNAi factor SET-32 deposits the transgenerational histone modification, H3K23me3. eLife, 9,
e54309. https://doi.org/10.7554/eLife.54309 [2] Kalinava, N., Ni, J. Z., Gajic, Z., Kim, M., Ushakov, H., & Gu, S. G. (2018). C. elegans Heterochromatin Factor SET-32 Plays an Essential Role in Transgenerational Establishment of Nuclear RNAi-Mediated Epigenetic Silencing. Cell reports, 25(8), 2273-2284.
e3. https://doi.org/10.1016/j.celrep.2018.10.086 [3] Woodhouse, R. M., & Ashe, A. (2019). Transgenerational Epigenetic Inheritance Is Revealed as a Multi-step Process by Studies of the SET-Domain Proteins SET-25 and SET-32. Epigenetics insights, 12, 2516865719844214. https://doi.org/10.1177/2516865719844214