Protein homeostasis is modulated by stress response pathways and its deficiency is a hallmark of aging. The integrated stress response (ISR) is a conserved stress-signaling pathway that tunes mRNA translation via phosphorylation of the translation initiation factor eIF2. ISR activation and translation initiation are finely balanced by eIF2 kinases and by the eIF2 guanine nucleotide exchange factor eIF2B. However, the role of the ISR during aging remains poorly understood. Using a genomic mutagenesis screen for longevity in Caenorhabditis elegans, we define a role of eIF2 modulation in aging. By inhibiting the ISR, dominant mutations in eIF2B enhance protein homeostasis and increase lifespan. Consistently, full ISR inhibition using phosphorylation-defective eIF2α or pharmacological ISR inhibition prolong lifespan. Lifespan extension through impeding the ISR occurs without a reduction in overall protein synthesis. Instead, we observe changes in the translational efficiency of a subset of mRNAs, of which the putative kinase kin-35 is required for lifespan extension. Evidently, lifespan is limited by the ISR and its inhibition may provide an intervention in aging.

The majority of genes are expressed in a temperature-dependent manner, but the way in which small RNAs may contribute to this effect is completely unknown as we currently lack an idea of how small RNA transcriptomes change as a function of temperature. Applying high-throughput sequencing techniques complemented by quantitative real-time PCR experiments, we demonstrate that altered ambient temperature induces drastic but reversible changes in sequence composition and total abundance of both miRNA and piRNA populations. Further, mRNA sequencing reveals that the expression of miRNAs and their predicted target transcripts correlates inversely, suggesting that temperature-responsive miRNAs drive adaptation to different ambient temperatures on the transcriptome level. Finally, we demonstrate that shifts in temperature affect both primary and secondary piRNA pools, and the observed aberrations are consistent with altered expression levels of the involved Piwi-pathway factors. We further reason that enhanced ping-pong processing at 29°C is driven by dissolved RNA secondary structures at higher temperatures, uncovering target sites that are not accessible at low temperatures. Together, our results show that small RNAs are an important part of epigenetic regulatory mechanisms that ensure homeostasis and adaptation under fluctuating environmental conditions.

Fragments of mature tRNAs have long been considered as mere degradation products without physiological function. However, recent reports show that tRNA-derived small RNAs (tsRNAs) play prominent roles in diverse cellular processes across a wide spectrum of species. Contrasting the situation in other small RNA pathways the mechanisms behind these effects appear more diverse, more complex and are generally less well understood. In addition, surprisingly little is known about the expression profiles of tsRNAs across different tissues and species. Here, we provide an initial overview of tsRNA expression in different species and tissues, revealing very high levels of 5' tRNA halves (5' tRHs) particularly in the primate hippocampus. We further modulated the regulation capacity of selected 5' tRHs in human cells by transfecting synthetic tsRNA mimics ("overexpression") or antisense-RNAs ("inhibition") and identified differentially expressed transcripts based on RNAseq. We then used a novel k-mer mapping approach to dissect the underlying targeting rules, suggesting

Longevity is often associated with stress resistance, but whether they are causally linked is incompletely understood. Here we investigate chemosensory defective Caenorhabditis elegans mutants that are long-lived and stress resistant. We find that mutants in the intraflagellar transport protein gene osm-3 were significantly protected from tunicamycin-induced ER stress. While osm-3 lifespan extension is dependent on the key longevity factor DAF-16/FOXO, tunicamycin resistance was not. osm-3 mutants are protected from bacterial pathogens, which is pmk-1 p38 MAP kinase dependent while TM resistance was pmk-1 independent. Expression of P-glycoprotein (PGP) xenobiotic detoxification genes was elevated in osm-3 mutants and their knockdown or inhibition with verapamil suppressed tunicamycin resistance. The nuclear hormone receptor nhr-8 was necessary to regulate a subset of PGPs. We thus identify a cell-nonautonomous regulation of xenobiotic detoxification and show that separate pathways are engaged to mediate longevity, pathogen resistance, and xenobiotic detoxification in osm-3 mutants.

Fragments of mature tRNAs have long been considered as mere degradation products without physiological function. However, recent reports show that tRNA fragments (tRFs) play prominent roles in diverse cellular processes across a wide spectrum of species. Contrasting the situation in other small RNA pathways the mechanisms behind these effects appear more diverse, more complex and are generally less well understood. In addition, surprisingly little is known about the expression profiles of tRFs across different tissues and species. Here, we provide an initial overview of tRF expression in different species and tissues, revealing very high tRF-levels particularly in the primate hippocampus.We further modulated the regulation capacity of selected tRFs in human cells by transfecting synthetic tRF mimics ("overexpression") or antisense-RNAs ("inhibition") and identified differentially expressed transcripts based on RNAseq. We then used a novel k-mer mapping approach to dissect the underlying targeting rules, demonstrating that 5' tRNA halves (5' tRHs) silence genes in a sequence-specific Jehn et al.2 manner, while the most efficient target sites align to the mid-region of the 5' tRH and are located within the CDS or 3' UTR of the target. This amends previous observations that tRFs guide Argonaut proteins to silence their targets via a miRNA-like 5' seed match and suggests a yet unknown mechanism of regulation. Finally, our data suggests that some 5' tRHs are also able to sequence-specifically stabilize mRNAs as upregulated mRNAs are also significantly enriched for 5' tRH target sites.