NRDE-1 is required for germline immortality.

NRDE-1 is required germline immortality and is a critical component of the transcriptional silencing pathway known as nuclear RNAi. Loss of the nrde-1 gene activity results in progressive accumulation of transgenerational stress which compromises the germline tissue and results in germ cell loss, ending ultimately in sterility. Using nrde-1, we paint a sketch of a germline stress and identify DAF-2, a component of the insulin signaling pathway, as well as piRNAs as significant contributors to this stress. Additionally, we explore the accumulation of stress by defining the developmental stage at which the sterility occurs. Due to its role in silencing, we conducted RNAseq on early vs sterile generation nrde-1 mutant animals to investigate the cause of its Germline Mortality and outline results in the expression of selfish genetic elements such as retrotransposons. Although these elements are expressed in sterile generation nrde-1 they were similarly upregulated in another nrde mutant that does not become sterile. Additionally, we have uncovered a list of 19 genes whose transcription is >2 fold upregulated in late generation nrde-1mutants that have accrued damage. Of these genes 42% correspond to the process of spermatogenesis, in agreement with other Mrt studies involving epigenetic transgenerational sterility. We explain this by showing that sperm are not necessary for sterility and that developmental delay occurs and may explain spermatogenesis gene misregulation.Doctor of Philosoph

Reduced Insulin/IGF-1 Signaling Restores Germ Cell Immortality to Caenorhabditis elegans Piwi Mutants

Defects in the Piwi/piRNA pathway lead to transposon desilencing and immediate sterility in many organisms. We found that the C. elegans Piwi mutant prg-1 became sterile after growth for many generations. This phenotype did not occur for RNA interference mutants with strong transposon silencing defects and was separable from the role of PRG-1 in transgene silencing. Brief periods of starvation extended the transgenerational lifespan of prg-1 mutants by stimulating the DAF-16/FOXO longevity transcription factor. Constitutive activation of DAF-16 via reduced daf-2 insulin/IGF-1 signaling immortalized prg-1 strains via RNA interference proteins and histone H3 lysine 4 demethylases. In late-generation prg-1 mutants, desilencing of repetitive segments of the genome occurred, and silencing of repetitive loci was restored in prg-1; daf-2 mutants. This study reveals an unexpected interface between aging and transgenerational maintenance of germ cells, where somatic longevity is coupled to a genome silencing pathway that promotes germ cell immortality in parallel to the Piwi/piRNA system

piRNAs Can Trigger a Multigenerational Epigenetic Memory in the Germline of C. elegans

SummaryTransgenerational effects have wide-ranging implications for human health, biological adaptation, and evolution; however, their mechanisms and biology remain poorly understood. Here, we demonstrate that a germline nuclear small RNA/chromatin pathway can maintain stable inheritance for many generations when triggered by a piRNA-dependent foreign RNA response in C.elegans. Using forward genetic screens and candidate approaches, we find that a core set of nuclear RNAi and chromatin factors is required for multigenerational inheritance of environmental RNAi and piRNA silencing. These include a germline-specific nuclear Argonaute HRDE1/WAGO-9, a HP1 ortholog HPL-2, and two putative histone methyltransferases, SET-25 and SET-32. piRNAs can trigger highly stable long-term silencing lasting at least 20 generations. Once established, this long-term memory becomes independent of the piRNA trigger but remains dependent on the nuclear RNAi/chromatin pathway. Our data present a multigenerational epigenetic inheritance mechanism induced by piRNAs.Graphical AbstractHighlights► Multigenerational inheritance and piRNAs converge on same nuclear silencing pathway ► HRDE1/WAGO-9 and chromatin factors required for inheritance of piRNA silencing ► piRNAs can induce multigenerational silencing for more than 20 generations. ► Long-term memory independent of piRNA triggers but remains dependent on nuclear pathwayMultigenerational inheritance and piRNAs converge on same silencing pathway, in which both nuclear WAGOs and chromatin factors are required. The piRNA trigger can be lost, but the nuclear silencing pathway maintains the silencing for more than 20 generations

Reduced Insulin/IGF-1 Signaling Restores Germ Cell Immortality to Caenorhabditis elegans Piwi Mutants

Defects in the Piwi/piRNA pathway lead to transposon desilencing and immediate sterility in many organisms. We found that the C. elegans Piwi mutant prg-1 became sterile after growth for many generations. This phenotype did not occur for RNAi mutants with strong transposon-silencing defects and was separable from the role of PRG-1 in transgene silencing. Brief periods of starvation extended the transgenerational lifespan of prg-1 mutants by stimulating the DAF-16/FOXO longevity transcription factor. Constitutive activation of DAF-16 via reduced daf-2 insulin/IGF-1 signaling immortalized prg-1 strains via RNAi proteins and histone H3 lysine 4 demethylases. In late-generation prg-1 mutants, desilencing of repetitive segments of the genome occurred, and silencing of repetitive loci was restored in prg-1; daf-2 mutants. This study reveals an unexpected interface between aging and transgenerational maintenance of germ cells, where somatic longevity is coupled to a genome-silencing pathway that promotes germ cell immortality in parallel to the Piwi/piRNA system