Project description:Protein function is controlled by the cellular proteostasis network. Proteostasis is energetically costly and those costs must be balanced with the energy needs of other physiological functions. Hypertonic stress causes widespread protein damage in C. elegans. Suppression and management of protein damage is essential for optimal survival under hypertonic conditions. ASH chemosensory neurons allow C. elegans to detect and avoid strongly hypertonic environments. We demonstrate that gene mutations that disrupt ASH mediated hypertonic avoidance behavior or genetic ablation of ASH neurons enhance survival during hypertonic stress. Enhanced survival is not due to altered systemic volume homeostasis or organic osmolyte accumulation. Instead, loss of ASH neuron function reduces protein damage in non-neuronal cells. Improved proteostasis capacity is due in part to upregulation of genes that play important roles in managing protein damage. We propose that inhibitory signaling from ASH neurons normally suppresses expression of genes required for non-neuronal cell proteostasis. Because all cells have the capacity to sense and respond to stressors, inhibitory neuronal signaling may be important for minimizing activation of cellular stress resistance and proteostasis pathways during short duration and less extreme stressors or stressors that can be avoided by behavioral changes. Neuronal regulation of systemic proteostasis allows the nervous system to monitor environmental variables and more effectively partition finite energy resources between different organismal processes. Our studies add to a growing body of work demonstrating that intercellular communication between neuronal and non-neuronal cells plays a critical role in integrating cellular stress resistance with other organismal physiological demands and associated energy costs. mRNA expression profiling of synchronized L4 stage wild-type N2 Bristol and VC1262 osm-9(ok1677) C. elegans strains under control (51mM NaCl) and hypertonic stress (200mM NaCl).

Project description:The plasticity of ageing suggests that longevity may be controlled epigenetically by specific alterations in chromatin state. The link between chromatin and ageing has mostly focused on histone deacetylation by the Sir2 family1, 2, but less is known about the role of other histone modifications in longevity. Histone methylation has a crucial role in development and in maintaining stem cell pluripotency in mammals3. Regulators of histone methylation have been associated with ageing in worms4, 5, 6, 7 and flies8, but characterization of their role and mechanism of action has been limited. Here we identify the ASH-2 trithorax complex9, which trimethylates histone H3 at lysine 4 (H3K4), as a regulator of lifespan in Caenorhabditis elegans in a directed RNA interference (RNAi) screen in fertile worms. Deficiencies in members of the ASH-2 complex—ASH-2 itself, WDR-5 and the H3K4 methyltransferase SET-2—extend worm lifespan. Conversely, the H3K4 demethylase RBR-2 is required for normal lifespan, consistent with the idea that an excess of H3K4 trimethylation—a mark associated with active chromatin—is detrimental for longevity. Lifespan extension induced by ASH-2 complex deficiency requires the presence of an intact adult germline and the continuous production of mature eggs. ASH-2 and RBR-2 act in the germline, at least in part, to regulate lifespan and to control a set of genes involved in lifespan determination. These results indicate that the longevity of the soma is regulated by an H3K4 methyltransferase/demethylase complex acting in the C. elegans germline. There are 23 samples in total. ASH-2 knock-down increases lifespan in a germline dependent manner. We examined ASH-2 regulated genes that are dependent on the presence of an intact germline using WT or glp-1(e2141ts) mutant worms which develop only 5-15 meiotic germ cells treated with either empty vector (EV) or ash-2 RNAi. We examined gene expression at the L3 stage (when we observe changes in H3K4me3) and at a mid life stage (day 8). The majority of ASH-2 controlled genes were regulated in a germline dependent manner. Samples were collected in triplicate for each condition (but Day 8 N2 (WT) E.V. #3 was excluded from all analysis due to quality issues).

Project description:Environmental stress-induced transgenerational epigenetic effects have been observed in various model organisms and human. The capacity and mechanism of such phenomena, particularly in animals, are poorly understood. In C. elegans, siRNA mediates transgenerational gene silencing through the germline nuclear RNAi pathway. At the organismal level, this pathway plays a transgenerational role in maintaining the germline immortality when C. elegans is under a mild heat stress. However, the underlying molecular mechanism is unknown. In this study, we performed a 12-generation temperature-shift experiment (15˚C->23˚C->15˚C) using the wild type (N2) and a mutant strain that lacks the germline-specific nuclear AGO protein HRDE-1/WAGO-9. We found that the temperature-sensitive mortal germline (Mrt) phenotype of the hrde-1 mutant is reversible, indicating a transgenerational cumulative but also reversible nature of the underlying molecular cause. By taking the whole-genome RNA and chromatin profiling approaches, we revealed an epigenetic role of HRDE-1 in repressing heat stress-induced transcriptional activation of over 280 genes, predominantly in or near LTR retrotransposons. Strikingly, for some of these elements, the heat stress-induced transcription becomes progressively activated in the hrde-1 mutant over several generations under heat stress. Furthermore, the effect of heat stress-induced transcription activation is heritable for at least two generations after the heat stress. Interestingly, the siRNA expression of these genes tend to be heat-inducible in the wild type animals, but not in the hrde-1 mutant, suggesting a role of siRNAs in repressing heat-inducible elements. Our study revealed a novel phenomenon of transgenerational feed-forward transcriptional activation, which is normally repressed in the wild type C. elegans by the germline nuclear RNAi pathway. It also provides a new paradigm to study epigenetic circuitry that connects the environment and gene regulation in the germline.

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Intestine-to-germline transmission of epigenetic information transgenerationally ensures systemic stress resistance in C. elegans

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