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Untangling the Role of H3K9 Methylations in Transgenerational Small RNA Inheritance

ABSTRACT: In C.elegans, disruption of the chromatin landscape produces transgenerational effects, such as inherited increase in lifespan and gradual loss of fertility. Inheritance of histone modifications can be induced by double strand RNA-derived heritable small RNAs. We show that the mortal germline phenotype which is typical to met-2 mutants, defective in H3K9 methylation, depends on HRDE-1, an argonaute that carries small RNAs across generations, and is accompanied by accumulated transgenerational misexpression of heritable small RNAs. We discovered that MET-2 inhibits small RNA inheritance, and as a consequence, induction of RNAi in met-2 mutants leads to permanent RNAi responses that do not terminate even after more than 30 generations. We found that potentiation of heritable RNAi in met-2 animals results from global hyperactivation of the small RNA inheritance machinery. Thus, changes in histone modifications can give rise to drastic transgenerational epigenetic effects, by controlling the overall potency of small RNA inheritance.

ORGANISM(S): Caenorhabditis elegans

PROVIDER: GSE94798 | GEO | 2017/03/30

SECONDARY ACCESSION(S): PRJNA374350

REPOSITORIES: GEO

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Stress Resets Transgenerational Small RNA Inheritance

Project description:Transgenerational inheritance is challenging basic concepts of heredity and achieving control over such responses is of great interest. In C. elegans nematodes, small RNAs are transmitted across generations to establish a transgenerational memory trace of ancestral environments. Inheritance of small RNAs is regulated by dedicated machinery and can be tuned by outside cues. Carryover of aberrant heritable small RNA responses was shown to be maladaptive and to induce sterility in certain cases. Here we show that various types of stress (starvation, high temperatures, and hyperosmotic conditions) but not non-stressful changes in cultivation, lead to resetting of small RNA inheritance. We found that stress leads to a genome-wide reduction in heritable small RNA levels and that mutants defective in different stress pathways exhibit irregular RNAi inheritance dynamics. Moreover, we discovered that resetting of heritable RNAi is orchestrated by MAPK pathway factors, the transcription factor SKN-1, and the MET-2 methyltransferase. Termination of small RNA inheritance, and the fact that this process depends on stress, could protect from run-on of environment-irrelevant heritable gene regulation.

2021-03-24 | GSE129988 | GEO

A Tunable Mechanism Determines the Transgenerational Duration of Small RNA Inheritance in C.elegans

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Germ Granules Govern Small RNA Inheritance

Project description:In C. elegans nematodes, components of liquid-like germ granules were shown to be required for transgenerational small RNA inheritance. Surprisingly, we show here that mutants with defective germ granules can nevertheless inherit potent small RNA-based silencing responses, but some of the mutants lose this ability after many generations of homozygosity. Animals mutated in pptr-1, which is required for stabilization of P granules in the early embryo, display extraordinarily strong heritable RNAi responses, lasting for tens of generations. Intriguingly, the RNAi capacity of descendants derived from mutants defective in the core germ granules proteins MEG-3 and MEG-4 is determined by the genotype of the ancestors, and changes transgenerationally. Further, whether the meg-3/4 mutant alleles were present in the paternal or maternal lineages lead to different transgenerational consequences. Small RNA inheritance, rather than maternal contribution of the germ granules themselves, mediates the transgenerational defects in RNAi of meg-3/4 mutants and their progeny. Accordingly, germ granule defects lead to heritable genome-wide mis-expression of endogenous small RNAs. Upon disruption of germ granules, hrde-1 mutants can inherit RNAi although HRDE-1 was previously thought to be absolutely required for RNAi inheritance. We propose that germ granules sort and shape the RNA pool, and that small RNA inheritance maintains this activity for multiple generations.

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The chromatin modifiers SET-25 and SET-32 are required for initiation but not long-term maintenance of transgenerational epigenetic inheritance

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The RNAi Inheritance Machinery of Caenorhabditis elegans

Project description:Gene silencing mediated by dsRNA (RNAi) can persist for multiple generations in C. elegans (termed RNAi inheritance). Here we describe the results of a forward genetic screen in C. elegans that has identified six factors required for RNAi inheritance: GLH-1/VASA, PUP-1/CDE-1, MORC-1, SET-32, and two novel nematode-specific factors that we term here (heritable RNAi defective) HRDE-2 and HRDE-4. The new RNAi inheritance factors exhibit mortal germline (Mrt) phenotypes, which we show is likely caused by epigenetic deregulation in germ cells. We also show that HRDE-2 contributes to RNAi inheritance by facilitating the binding of small RNAs to the inheritance Argonaute (Ago) HRDE-1. Together, our results identify additional components of the RNAi inheritance machinery whose sequence conservation provides insights into the molecular mechanism of RNAi inheritance, further our understanding of how the RNAi inheritance machinery promotes germline immortality, and show that HRDE-2 couples the inheritance Ago HRDE-1 with the small RNAs it needs to direct RNAi inheritance and germline immortality.

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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.

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A nuclear Argonaute promotes germline immortality and epigenetic inheritance across generations

Project description:dsRNA-mediated gene silencing (RNAi) can be inherited for multiple generations in C. elegans. To understand this process we conducted a genetic screen for animals defective for transmitting RNAi silencing signals to future generations. This screen identified the gene heritable RNAi defective (hrde)-1. hrde-1 encodes an Argonaute (Ago) that associates with siRNAs in germ cells of the progeny of animals exposed to dsRNA. In nuclei of these germ cells, HRDE-1 engages the Nrde nuclear RNAi pathway to promote RNAi inheritance, and directs H3K9me3 chromatin marks at RNAi targeted genomic loci. Under normal growth conditions, HRDE-1 associates with endogenously expressed small RNAs, which direct nuclear gene silencing in germ cells. In RNAi inheritance mutant animals, silencing is lost over generational time. Concurrently, RNAi inheritance mutant animals exhibit progressively worsening germline defects that ultimately lead to sterility. These results establish that the Ago HRDE-1 directs gene-silencing events in germ cell nuclei, which are required for multi-generational RNAi inheritance and immortality of the germ cell lineage. We propose that C. elegans use the RNAi inheritance machinery to transmit epigenetic information, accrued by past generations, into future generations to ensure immortality of the germ cell lineage. H3K9me3 Chip-IP for C. elegans strains nrde-3, nrde-4, glp-4. Small RNA-seq for small RNAs co-immunoprecipitated with HRDE-1

2012-07-30 | E-GEOD-38041 | biostudies-arrayexpress

A nuclear Argonaute promotes germline immortality and epigenetic inheritance across generations

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A membrane-associated condensate ensures paternal epigenetic inheritance in C. elegans

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2021-03-26 | PXD019099 | Pride

Small RNA-mediated transgenerational silencing of histone genes impairs fertility in piRNA mutants

Project description:PIWI-interacting RNAs (piRNAs) promote fertility in many animals. Yet, whether this is due to their conserved role in repressing repetitive elements (REs) or other functions remains unclear. Here, we show that the progressive loss of fertility in Caenorhabditis elegans lacking piRNAs is not caused by derepression of REs or other piRNA targets, but rather mediated by the epigenetic silencing of all the replicative histone genes. In the absence of piRNAs, downstream components of the piRNA pathway relocalize from germ granules and piRNA targets to histone mRNAs to synthesize antisense small RNAs (sRNAs) and induce transgenerational silencing. Removal of the downstream components of the piRNA pathway is sufficient to restore histone mRNA expression and fertility in piRNA mutants, and the inheritance of histone sRNAs in wild-type worms adversely affects their fertility for multiple generations. We conclude that the transgenerational silencing of histone genes contributes to the progressive loss of fertility in piRNA mutants and that coupling piRNAs and histone silencing may serve to maintain piRNAs production across evolution.

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