Intestine-to-Germline Transmission of Epigenetic Information Intergenerationally Ensures Systemic Stress Resistance in C. elegans

Modulation by NPY/NPF-like receptor underlies experience-dependent, sexually dimorphic learning

The evolutionary paths taken by each sex within a given species sometimes diverge, resulting in behavioral differences. Given their distinct needs, the mechanism by which each sex learns from a shared experience is still an open question. Here, we reveal sexual dimorphism in learning: C. elegans males do not learn to avoid the pathogenic bacteria PA14 as efficiently and rapidly as hermaphrodites. Notably, neuronal activity following pathogen exposure was dimorphic: hermaphrodites generate robust representations, while males, in line with their behavior, exhibit contrasting representations. Transcriptomic and behavioral analysis revealed that the neuropeptide receptor npr-5, an ortholog of the mammalian NPY/NPF-like receptor, regulates male learning by modulating neuronal activity. Furthermore, we show the dependency of the males' decision-making on their sexual status and demonstrate the role of npr-5 as a modulator of incoming sensory cues. Taken together, these findings illustrate how neuromodulators drive sex-specific behavioral plasticity in response to a shared experience.

Cadmium exposure induces multigenerational inheritance of germ cell apoptosis and fertility suppression in Caenorhabditis elegans

Cadmium is a significant environmental pollutant that poses a substantial health hazard to humans due to its propensity to accumulate in the body and resist excretion. We have a comprehensive understanding of the damage caused by Cd exposure and the mechanisms of tolerance, however, the intricate mechanisms underlying multigenerational effects resulting from Cd exposure remain poorly understood. In this study, Caenorhabditis elegans were used as a model organism to investigate Cd-induced multigenerational effects and its association with epigenetic modifications. The results showed that Cd exposure leads to an increase in germ cell apoptosis and a decrease in fertility, which can be passed down to subsequent generations. Further analysis revealed that transcription factors DAF-16/FOXO and SKN-1/Nrf2 play essential roles in responding to Cd exposure and in the transgenerational induction of germ cell apoptosis. Additionally, histone H3K4 trimethylation (H3K4me3) marks stress-responsive genes and enhances their transcription, ultimately triggering multigenerational germ cell apoptosis. This study provides compelling evidence that the detrimental effects of Cd on the reproductive system can be inherited across generations. These findings enhance our understanding of the multigenerational effects of environmental pollutants and may inform strategies for the prevention and control of such pollutants.

MYST family histone acetyltransferases regulate reproductive diapause initiation

Histone acetylation, a crucial epigenetic mechanism, has been suggested to play a role in diapause regulation, but this has not been confirmed through gene loss-of-function studies. In this work, we investigated the involvement of MYST family genes, which are key writers of histone acetylation, in initiating reproductive diapause using the cabbage beetle Colaphellus bowringi as a model. We identified C. bowringi orthologs of MYST, including Tip60, KAT6A, KAT7, and KAT8, from previous transcriptomes. Analyses of phylogenetic trees and protein domains indicated that these MYST proteins are structurally conserved across animal species. Expression of these MYST genes was found to be enriched in heads and ovaries of C. bowringi. Under reproductive photoperiod conditions, RNAi targeting MYST genes, especially KAT8, suppressed ovarian growth and yolk deposition, resembling the characteristics of diapausing ovaries. Additionally, KAT8 knockdown led to the upregulation of diapause-related genes, such as heat shock proteins and diapause protein 1, and the emergence of diapause-like guts. Moreover, KAT8 knockdown reduced the expression of a crucial enzyme involved in juvenile hormone (JH) biosynthesis, likely due to decreased H4K16ac levels. Consequently, our findings suggest that MYST family genes, specifically KAT8, influence the JH signal, thereby regulating the initiation of reproductive diapause.

Genome-wide association and environmental suppression of the mortal germline phenotype of wild C. elegans

The animal germline lineage needs to be maintained along generations. However, some Caenorhabditis elegans wild isolates display a mortal germline phenotype, leading to sterility after several generations at 25°C. Using a genome-wide association approach, we detect a significant peak on chromosome III around 5 Mb, confirmed by introgressions. Thus, a seemingly deleterious genotype is maintained at intermediate frequency in the species. Environmental rescue is a likely explanation, and indeed associated bacteria and microsporidia suppress the phenotype of wild isolates as well as mutants in small RNA inheritance (nrde-2) and histone modifications (set-2). Escherichia coli strains of the K-12 lineage suppress the phenotype compared to B strains. By shifting a wild strain from E. coli K-12 to E. coli B, we find that memory of the suppressing condition is maintained over several generations. Thus, the mortal germline phenotype of wild C. elegans is in part revealed by laboratory conditions and may represent variation in epigenetic inheritance and environmental interactions. This study also points to the importance of non-genetic memory in the face of environmental variation.

β-Carotene enhances the expression of inflammation-related genes and histone H3 K9 acetylation, K4 dimethylation, and K36 trimethylation around these genes in juvenile macrophage-like THP-1 cells

β-Carotene is converted into vitamin A in the body and can remove reactive oxygen species. However, it is still unclear whether β-carotene alters the expression levels of inflammation-related genes in macrophages and how this is regulated. In the present study, we investigated whether the administration of β-carotene under hyperglycemic conditions altered the expression level of inflammation-related genes and whether any observed differences were associated with changes in histone modifications in juvenile macrophage-like THP-1 cells. THP-1 cells (from a human monocytic leukemia cell line) were cultured in low glucose (5 mM), high glucose (25 mM), or high glucose (25 mM) + β-carotene (5 μM) media for 1 day, and mRNA expression levels of genes related to oxidative stress and inflammation, and histone modifications were determined by mRNA microarray and qRT-PCR analyses, and chromatin immunoprecipitation assays, respectively. The expression of inflammation-related genes, such as IL31RA, CD38, and NCF1B, and inflammation-associated signaling pathway genes, such as ITGAL, PRAM1, and CSF3R, were upregulated by β-carotene under high-glucose conditions. Under these conditions, histone H3 lysine 4 (K4) demethylation, H3K36 trimethylation, and H3K9 acetylation around the CD38, NCF1B, and ITGAL genes were higher in β-carotene-treated cells than in untreated cells. Treatment of juvenile macrophage-like THP-1 cells with β-carotene under these high glucose conditions induced the expression of inflammation-related genes, K9 acetylation, and K4 di- and K36 trimethylation of histone H3 around these genes.

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β-Carotene enhances expression of inflammatory genes in THP-1 cells.

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β-Carotene enhances histone H3 K9 acetylation around inflammatory genes.

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β-carotene enhances K4 di- and K36 tri-methylation around inflammatory genes.

Interspecies effectors of a transgenerational memory of bacterial infection in Caenorhabditis elegans

The inheritance of memory is an adaptive trait. Microbes challenge the immunity of organisms and trigger behavioral adaptations that can be inherited, but how bacteria produce inheritance of a trait is unknown. We use Caenorhabditis elegans and its bacteria to study the transgenerational RNA dynamics of interspecies crosstalk leading to a heritable behavior. A heritable response of C. elegans to microbes is the pathogen-induced diapause (PIDF), a state of suspended animation to evade infection. We identify RsmY, a small RNA involved in quorum sensing in Pseudomonas aeruginosa as a trigger of PIDF. The histone methyltransferase (HMT) SET-18/SMYD3 and the argonaute HRDE-1, which promotes multi-generational silencing in the germline, are also needed for PIDF initiation. The HMT SET-25/EHMT2 is necessary for memory maintenance in the transgenerational lineage. Our work is a starting point to understanding microbiome-induced inheritance of acquired traits, and the transgenerational influence of microbes in health and disease.

The Intestine as a Lifespan- and Proteostasis-Promoting Signaling Tissue

In multicellular organisms such as Caenorhabditis elegans, cellular stress stimuli and responses are communicated between tissues to promote organismal health- and lifespan. The nervous system is the predominant regulator of cell nonautonomous proteostasis that orchestrates systemic stress responses to integrate both internal and external stimuli. This review highlights the role of the intestine in mediating cell nonautonomous stress responses and explores recent findings that suggest a central role for the intestine to regulate organismal proteostasis. As a tissue that receives and further transduces signals from the nervous system in response to dietary restriction, heat- and oxidative stress, and hypoxia, we explore evidence suggesting the intestine is a key regulatory organ itself. From the perspective of naturally occurring stressors such as dietary restriction and pathogen infection we highlight how the intestine can function as a key regulator of organismal proteostasis by integrating insulin/IGF-like signaling, miRNA-, neuropeptide- and metabolic signaling to alter distal tissue functions in promoting survival, health- and lifespan.

Molecular insights into transgenerational inheritance of stress memory

There is accumulating evidence to show that environmental stressors can regulate a variety of phenotypes in descendants through germline-mediated epigenetic inheritance. Studies of model organisms exposed to environmental cues (e.g., diet, heat stress, toxins) indicate that altered DNA methylations, histone modifications, or non-coding RNAs in the germ cells are responsible for the transgenerational effects. In addition, it has also become evident that maternal provision could provide a mechanism for the transgenerational inheritance of stress adaptations that result from ancestral environmental cues. However, how the signal of environmentally-induced stress response transmits from the soma to the germline, which may influence offspring fitness, remains largely elusive. Small RNAs could serve as signaling molecules that transmit between tissues and even across generations. Furthermore, a recent study revealed that neuronal mitochondrial perturbations induce a transgenerational induction of the mitochondrial unfolded protein response mediated by a Wnt-dependent increase in mitochondrial DNA levels. Here, we review recent work on the molecular mechanism by which parental experience can affect future generations and the importance of soma-to-germline signaling for transgenerational inheritance.

Transmission of chromatin states across generations in C. elegans

Epigenetic inheritance refers to the transmission of phenotypes across generations without affecting the genomic DNA sequence. Even though it has been documented in many species in fungi, animals and plants, the mechanisms underlying epigenetic inheritance are not fully uncovered. Epialleles, the heritable units of epigenetic information, can take the form of several biomolecules, including histones and their post-translational modifications (PTMs). Here, we review the recent advances in the understanding of the transmission of histone variants and histone PTM patterns across generations in C. elegans. We provide a general overview of the intergenerational and transgenerational inheritance of histone PTMs and their modifiers and discuss the interplay among different histone PTMs. We also evaluate soma-germ line communication and its impact on the inheritance of epigenetic traits.

Shaping longevity early in life: developmental ROS and H3K4me3 set the clock

Studies in Caenorhabditis elegans have revealed that even a genetically identical population of animals exposed to the same environment displays a remarkable level of variability in individual lifespan. Stochasticity factors, occurring seemingly by chance or at random, are thought to account for a large part of this variability. Recent studies in our lab using C. elegans now revealed that naturally occurring variations in the levels of reactive oxygen species experienced early in life contribute to the observed lifespan variability, and likely serve as stochasticity factors in aging. Here, we will highlight how developmental events can positively shape lifespan and stress responses via a redox-sensitive epigenetic regulator, and discuss the outstanding questions and future directions on the complex relationship between reactive oxygen species and aging.

The Heritability of Behaviors Associated With the Host Gut Microbiota

What defines whether the interaction between environment and organism creates a genetic memory able to be transferred to subsequent generations? Bacteria and the products of their metabolism are the most ubiquitous biotic environments to which every living organism is exposed. Both microbiota and host establish a framework where environmental and genetic factors are integrated to produce adaptive life traits, some of which can be inherited. Thus, the interplay between host and microbe is a powerful model to study how phenotypic plasticity is inherited. Communication between host and microbe can occur through diverse molecules such as small RNAs (sRNAs) and the RNA interference machinery, which have emerged as mediators and carriers of heritable environmentally induced responses. Notwithstanding, it is still unclear how the organism integrates sRNA signaling between different tissues to orchestrate a systemic bacterially induced response that can be inherited. Here we discuss current evidence of heritability produced by the intestinal microbiota from several species. Neurons and gut are the sensing systems involved in transmitting changes through transcriptional and post-transcriptional modifications to the gonads. Germ cells express inflammatory receptors, and their development and function are regulated by host and bacterial metabolites and sRNAs thus suggesting that the dynamic interplay between host and microbe underlies the host's capacity to transmit heritable behaviors. We discuss how the host detects changes in the microbiota that can modulate germ cells genomic functions. We also explore the nature of the interactions that leave permanent or long-term memory in the host and propose mechanisms by which the microbiota can regulate the development and epigenetic reprogramming of germ cells, thus influencing the inheritance of the host. We highlight the vast contribution of the bacterivore nematode C. elegans and its commensal and pathogenic bacteria to the understanding on how behavioral adaptations can be inter and transgenerational inherited.

Microbial colonization induces histone acetylation critical for inherited gut-germline-neural signaling

The gut-neural axis plays a critical role in the control of several physiological processes, including the communication of signals from the microbiome to the nervous system, which affects learning, memory, and behavior. However, the pathways involved in gut-neural signaling of gut-governed behaviors remain unclear. We found that the intestinal distension caused by the bacterium Pseudomonas aeruginosa induces histone H4 Lys8 acetylation (H4K8ac) in the germline of Caenorhabditis elegans, which is required for both a bacterial aversion behavior and its transmission to the next generation. We show that induction of H4K8ac in the germline is essential for bacterial aversion and that a 14-3-3 chaperone protein family member, PAR-5, is required for H4K8ac. Our findings highlight a role for H4K8ac in the germline not only in the intergenerational transmission of pathogen avoidance but also in the transmission of pathogenic cues that travel through the gut-neural axis to control the aversive behavior.

This study shows that microbial colonization of the intestine of the nematode Caenorhabditis elegans intestine induces changes in the germline that not only influence the inheritance of pathogen avoidance but also the transmission of pathogenic cues that travel through the gut-neural axis to control aversive behavior.

Intertissue small RNA communication mediates the acquisition and inheritance of hormesis in Caenorhabditis elegans

Environmental conditions can cause phenotypic changes, part of which can be inherited by subsequent generations via soma-to-germline communication. However, the signaling molecules or pathways that mediate intertissue communication remain unclear. Here, we show that intertissue small RNA communication systems play a key role in the acquisition and inheritance of hormesis effects – stress-induced stress resistance – in Caenorhabditis elegans. The miRNA-processing enzyme DRSH-1 is involved in both the acquisition and the inheritance of hormesis, whereas worm-specific Argonaute (WAGO) proteins, which function with endo-siRNAs, are involved only in its inheritance. Further analyses demonstrate that the miRNA production system in the neuron and the small RNA transport machinery in the intestine are both essential for its acquisition and that both the transport of small RNAs in the germline and the germline Argonaute HRDE-1 complex are required for its inheritance. Our results thus demonstrate that overlapping and distinct roles of small RNA systems in the acquisition and inheritance of hormesis effects.

Okabe et al. show that the miRNA production system in the neuron and the small RNA transport machinery in the intestine are required for the acquisition of hormesis. For its inheritance, both the transport of small RNAs in the germline and the germline Argonaute HRDE-1 complex are needed, highlighting distinct contribution of small RNA systems to hormesis.

Stressful development: integrating endoderm development, stress, and longevity

In addition to performing digestion and nutrient absorption, the intestine serves as one of the first barriers to the external environment, crucial for protecting the host from environmental toxins, pathogenic invaders, and other stress inducers. The gene regulatory network (GRN) governing embryonic development of the endoderm and subsequent differentiation and maintenance of the intestine has been well-documented in C. elegans. A key regulatory input that initiates activation of the embryonic GRN for endoderm and mesoderm in this animal is the maternally provided SKN-1 transcription factor, an ortholog of the vertebrate Nrf1 and 2, which, like C. elegans SKN-1, perform conserved regulatory roles in mediating a variety of stress responses across metazoan phylogeny. Other key regulatory factors in early gut development also participate in stress response as well as in innate immunity and aging and longevity. In this review, we discuss the intersection between genetic nodes that mediate endoderm/intestine differentiation and regulation of stress and homeostasis. We also consider how direct signaling from the intestine to the germline, in some cases involving SKN-1, facilitates heritable epigenetic changes, allowing transmission of adaptive stress responses across multiple generations. These connections between regulation of endoderm/intestine development and stress response mechanisms suggest that varying selective pressure exerted on the stress response pathways may influence the architecture of the endoderm GRN, thereby leading to genetic and epigenetic variation in early embryonic GRN regulatory events.