Lev, Itamar et al. (2019) International Worm Meeting "Untangling the role of H3K9me3 in transgenerational small RNA inheritance."

Gingold, Hila, Rechavi, Oded, Lev, Itamar

[International Worm Meeting, 2019]

Small RNA-mediated gene regulatory responses are inherited in Caenorhabditis elegans across multiple generations. In addition, exposure to a number of environmental challenges, such as viral infection, starvation, and heat induces heritable physiological responses in C. elegans. In certain cases, the inheritance of such responses can be linked to heritable small RNAs or chromatin modifications and was suggested to prepare the progeny for the environmental challenges that the ancestors met. A feed-forward loop between heritable small RNAs and 'repressive' histone marks maintains the heritable information in various organisms. Previously, we showed that MET-2, an H3K9-mono/di-methyltransferase, inhibits dsRNA-induced small RNA inheritance. Accordingly, induction of RNAi in met-2 mutants leads to permanent silencing of the RNAi-targeted gene for many generations. Recently, we found an asymmetry in the function of the RNAi-induced H3K9me3. The H3K9-tri-methyltransferases SET-25 and SET-32 promote heritable silencing of the foreign gene gfp, but are dispensable for inheritance of silencing of the endogenous gene oma-1. Genome-wide analysis of heritable endogenous-small interfering RNAs (endo-siRNAs) revealed that endo-siRNAs that depend on SET-25 and SET-32 target newly acquired and highly H3K9me3-marked genes. Here we will present new insights on epigenetic inheritance and the roles that heritable small RNAs and chromatin modifications play.

Lev, Itamar et al. (2017) International Worm Meeting "Untangling the Role of H3K9 Methylations in Transgenerational Small RNA Inheritance."

Bril, Roberta, Gingold, Hila, Rechavi, Oded, Anava, Sarit, Seroussi, Uri, Lev, Itamar

[International Worm Meeting, 2017]

In recent years transgenerational inheritance of acquired traits has been described in various species. Both small interfering RNAs (siRNAs) and chromatin modifications have been implicated in the maintenance of such heritable responses. In plants and yeast, a self-reinforcing feedforward loop was described, where nuclear siRNAs direct histone methylation at pericentromeric regions and in return, the siRNA machinery is recruited to pericentromeric methylated histones to synthesize additional siRNAs. In Caenorhabditis elegans, double-stranded RNA-induced RNA interference (RNAi) can produce long-term heritable silencing responses that involve the production of "secondary" siRNAs and histone methylation of the targeted locus. Recently, we showed that MET-2, a histone-H3 Lysine-9 mono/di- methyltransferase, suppresses transgenerational RNAi inheritance indirectly by affecting small RNA biogenesis. The current work discusses how chromatin modifications affect small RNA biogenesis and the different requirements for heritable silencing of transgenes and endogenous genes.

Agarwal, Priti et al. (2021) International Worm Meeting "Distal tip cell-specific mRNA profiling sheds light on the molecular mechanism of gonad morphogenesis"

Antonova, Olga, Agarwal, Priti, Anava, Sarit, Gingold, Hila, Rechavi, Oded, Zaidel-Bar, Ronen

[International Worm Meeting, 2021]

Cell motility is essential for the normal development and physiology of an organism. In C. elegans, the stereotypical U-shaped gonad is formed by the directional chemotactic movement of two somatic cells, known as Distal-Tip Cells (DTCs), whose movement is divided into three phases. In phase I (early L3 larval stage) they move along the ventral surface. Phase II (late L3 stage) involves two 90° turns, and finally in phase III (early L4 larval stage) the DTCs move along the dorsal surface towards the midbody of the worm. Migration halts during the late L4 stage. While multiple genetic screens have identified general regulators of gonad morphogenesis, a DTC-specific role has remained largely unexplored. To address this, we isolated GFP-labelled DTCs from different stages of development and performed RNA-sequencing, to characterize and compare the transcriptome of migratory DTCs (late L3 and early L4 stage) with non-migratory DTCs (late L4 and adult stage). We identified between 1700 to 3000 genes that are upregulated in each of the larval and adult stage DTC relative to other cell types. We confirmed the identification of the few DTC-specific transcripts known in the literature. The overlap between the genes we found upregulated in DTCs and the published germline-enriched genes (Reinke et al., 2004) is only 0.9 to 6.4%. Furthermore, we found that among the 99 genes identified in a genome-wide RNAi screen (Cram et al., 2006) to have a role in DTC migration, 43 genes are enriched in the migratory early L4 stage DTC transcriptome, while only 7 genes are present in the immobile adult stage DTCs. Taken together, it appears our dataset of cell-specific and stage-specific DTC transcripts is highly accurate. A bioinformatic functional analysis of the migratory DTC transcripts revealed enrichment of genes related to neuronal guidance, cytoskeleton, signaling, and membrane trafficking. Currently, we are performing a DTC-specific RNAi screen to identify the novel cell-autonomous regulators of DTC migration which in turn guides gonad morphogenesis. Identifying these regulators will help us to decipher the molecular mechanisms of DTC migration deployed in a three-dimensional microenvironment, which will eventually give insight into the mechanism of gonadogenesis.

Posner, Rachel et al. (2017) International Worm Meeting "Gene regulation via non-cell autonomous acting small RNAs in C. elegans."

Gingold, Hila, Hobert, Oliver, Posner, Rachel, Azmon, Eran, Anava, Sarit, Rechavi, Oded, Star, Ekaterina, Bracha, Shahar

[International Worm Meeting, 2017]

Exposure of C. elegans to artificial dsRNA can trigger exogenous small RNA-mediated silencing that transmits from somatic cells to the germline, and persists for multiple generations. However, it is unknown whether endogenous types of small RNAs (miRNAs, piRNAs and endo-siRNAs) produce systematic responses and what type of effect they may have on gene regulation. Our recent results suggest that endogenous siRNAs act in a non-cell autonomous manner, orchestrating gene silencing between tissues. We will present a dissection of the major components of the RNAi pathway required for non-cell autonomous gene regulation by endo-siRNAs and provide evidence possibly linking the regulation of physiological phenotypes to small RNAs mobilizing between tissues.