In Caenorhabditis elegans and Drosophila melanogaster, removing the germline precursor cells increases lifespan. In worms, and possibly also in flies, this lifespan extension requires the presence of somatic reproductive tissues. How the somatic gonad signals other tissues to increase lifespan is not known. The lifespan increase triggered by loss of the germ cells is known to require sterol hormone signaling, as reducing the activity of the nuclear hormone receptor DAF-12, or genes required for synthesis of the DAF-12 ligand dafachronic acid, prevents germline loss from extending lifespan. In addition to sterol signaling, the FOXO transcription factor DAF-16 is required to extend lifespan in animals that lack germ cells. DAF-12/NHR is known to assist with the nuclear accumulation of DAF-16/FOXO in these animals, yet we find that loss of DAF-12/NHR has little or no effect on the expression of at least some DAF-16/FOXO target genes. In this study, we show that the DAF-12-sterol signaling pathway has a second function to activate a distinct set of genes and extend lifespan in response to the somatic reproductive tissues. When germline-deficient animals lacking somatic reproductive tissues are given dafachronic acid, their expression of DAF-12/NHR-dependent target genes is restored and their lifespan is increased. Together, our findings indicate that in C. elegans lacking germ cells, the somatic reproductive tissues promote longevity via steroid hormone signaling to DAF-12.
... In addition to being expressed in the nervous system, genes regulated by insulin signaling are also highly expressed in the intestine [43,44]. As the RNA isolated from L1 animals hatched in the absence of food shows decreased gene expression similar to neural cells, this suggests that loss of adr-2 can potentially result in altered insulin-signaling in both neural and intestinal cells. ...
... To further validate that neural ADR-2 regulates insulin signaling regulated genes throughout the animal, confocal microscopy was performed to monitor expression of one of these genes, dod-24, upon loss of adr-2 in whole animals. Synchronized L1 animals expressing GFP driven by the dod-24 promoter [43] were analyzed. In wild-type animals, transcription from the dod-24 promoter was observed in neural as well as intestinal cells as expected [43] (Fig 2B). ...
... Synchronized L1 animals expressing GFP driven by the dod-24 promoter [43] were analyzed. In wild-type animals, transcription from the dod-24 promoter was observed in neural as well as intestinal cells as expected [43] (Fig 2B). Upon loss of adr-2, decreased GFP expression was observed throughout the animal (Fig 2B), which is consistent with the qPCR analysis of dod-24 expression (Fig 1C). ...
The ability to alter gene expression programs in response to changes in environmental conditions is central to the ability of an organism to thrive. For most organisms, the nervous system serves as the master regulator in communicating information about the animal’s surroundings to other tissues. The information relay centers on signaling pathways that cue transcription factors in a given cell type to execute a specific gene expression program, but also provide a means to signal between tissues. The transcription factor PQM-1 is an important mediator of the insulin signaling pathway contributing to longevity and the stress response as well as impacting survival from hypoxia. Herein, we reveal a novel mechanism for regulating PQM-1 expression specifically in neural cells of larval animals. Our studies reveal that the RNA-binding protein (RBP), ADR-1, binds to pqm-1 mRNA in neural cells. This binding is regulated by the presence of a second RBP, ADR-2, which when absent leads to reduced expression of both pqm-1 and downstream PQM-1 activated genes. Interestingly, we find that neural pqm-1 expression is sufficient to impact gene expression throughout the animal and affect survival from hypoxia, phenotypes that we also observe in adr mutant animals. Together, these studies reveal an important posttranscriptional gene regulatory mechanism in Caenorhabditis elegans that allows the nervous system to sense and respond to environmental conditions to promote organismal survival from hypoxia.
... In addition to being expressed in the nervous system, genes regulated by insulin signaling are also highly expressed in the intestine [43,44]. As the RNA isolated from L1 animals hatched in the absence of food shows decreased gene expression similar to neural cells, this suggests that loss of adr-2 can potentially result in altered insulinsignaling in both neural and intestinal cells. ...
... To further validate that neural ADR-2 regulates insulin signaling regulated genes throughout the animal, confocal microscopy was performed to monitor expression of one of these genes, dod-24, upon loss of adr-2 in whole animals. Synchronized L1 animals expressing GFP driven by the dod-24 promoter [43] were analyzed. In wildtype animals, transcription from the dod-24 promoter was observed in neural as well as intestinal cells as expected [43] ( Figure 2B). ...
... Synchronized L1 animals expressing GFP driven by the dod-24 promoter [43] were analyzed. In wildtype animals, transcription from the dod-24 promoter was observed in neural as well as intestinal cells as expected [43] ( Figure 2B). Upon loss of adr-2, decreased GFP expression was observed throughout the animal ( Figure 2B), which is consistent with the qPCR analysis of dod-24 expression ( Figure 1C). ...
The ability to alter gene expression programs in response to changes in environmental conditions is central to the ability of an organism to thrive. For most organisms, the nervous system serves as the master regulator in communicating information about the animal’s surroundings to other tissues. The information relay centers on signaling pathways that cue transcription factors in a given cell type to execute a specific gene expression program, but also provide a means to signal between tissues. The transcription factor PQM-1 is an important mediator of the insulin signaling pathway contributing to longevity and the stress response as well as impacting survival from hypoxia. Herein, we reveal a novel mechanism for regulating PQM-1 expression specifically in neural cells of larval animals. Our studies reveal that the RNA binding protein, ADR-1, binds to pqm-1 mRNA in neural cells. This binding is regulated by the presence of a second RNA binding protein, ADR-2, which when absent leads to reduced expression of both pqm-1 and downstream PQM-1 activated genes. Interestingly, we find that neural pqm-1 expression is sufficient to impact gene expression throughout the animal and affect survival from hypoxia; phenotypes that we also observe in adr mutant animals. Together, these studies reveal an important post-transcriptional gene regulatory mechanism that allows the nervous system to sense and respond to environmental conditions to promote organismal survival from hypoxia.
... Its activation is mediated by the ligand dafachronic acid (DA), a cholesterol-derived hormone (Motola et al., 2006). However, significant lifespan extension can be induced in animals lacking germline and somatic reproductive tissues by supplementation with DA (Yamawaki et al., 2010). This suggests that the somatic gonad triggers the production of the DAF-12 ligand in animals lacking only the germline (Gerisch et al., 2007). ...
... The enzyme DAF-9, essential for the synthesis of DA, is expressed in the somatic gonad. This evidence is suggestive of the role of DA as the somatic pro-longevity signal in germline-less C. elegans (Yamawaki et al., 2010). A simple model is that somatic gonad can stimulate DA production when the germline cells are removed. ...
The gonad has become a central organ for understanding aging in C. elegans , as removing the proliferating stem cells in the germline results in significant lifespan extension. Similarly, when starvation in late larval stages leads to the quiescence of germline stem cells the adult nematode enters reproductive diapause, associated with an extended lifespan. This review summarizes recent advancements in identifying the mechanisms behind gonad-mediated lifespan extension, including comparisons with other nematodes and the role of lipid signaling and transcriptional changes. Given that the gonad also mediates lifespan regulation in other invertebrates and vertebrates, elucidating the underlying mechanisms may help to gain new insights into the mechanisms and evolution of aging.
... The reproductive system of C. elegans is one of the most sexually dimorphic tissues in the animal, with many components differing between hermaphrodites and males. Multiple studies demonstrated that germline removal in C. elegans or Pristionchus pacificus promotes longevity and increases innate immunity by activating the transcription factor DAF-16/FOXO that is repressed by insulin/insulin-like growth factor signaling (IIS) (53,(73)(74)(75). ...
Gap junctions mediate intercellular communications across cellular networks in the nervous and immune systems. Yet their roles in intestinal innate immunity are poorly understood. Here, we show that the gap junction/innexin subunit inx-14 acts in the C. elegans gonad to attenuate intestinal defenses to Pseudomonas aeruginosa PA14 infection through the PMK-1/p38 pathway. RNA-Seq analyses revealed that germline-specific inx-14 RNAi downregulated Notch/GLP-1 signaling, while lysosome and PMK-1/p38 pathways were upregulated. Consistently, disruption of inx-14 or glp-1 in the germline enhanced resistance to PA14 infection and upregulated lysosome and PMK-1/p38 activity. We show that lysosome signaling functions downstream of the INX-14/GLP-1 signaling axis and upstream of PMK-1/p38 pathway to facilitate intestinal defense. Our findings expand the understanding of the links between the reproductive system and intestinal defense, which may be evolutionarily conserved in higher organism.
... Further, we speculated that the communication could be through hormonal signaling which can aid in the soma-germ line crosstalk. Earlier studies have elucidated the role of the DAF-12 nuclear hormone receptor/steroid hormone signaling pathway in life span extension by germ cell perturbation (Hsin and Kenyon, 1999;Yamawaki et al., 2010). Moreover, DAF-12 bound to its ligand, dafachronic acid (DA), has also been shown to negatively affect germ cell proliferation (Mukherjee et al., 2017). ...
Germ line integrity is critical for progeny fitness. Organisms deploy the DNA damage response (DDR) signaling to protect the germ line from genotoxic stress, facilitating the cell-cycle arrest of germ cells and DNA repair or their apoptosis. Cell-autonomous regulation of germ line quality in response to DNA damage is well-studied; however, how quality is enforced cell non-autonomously on sensing somatic D NA damage is less known. Using Caenorhabditis elegans, we show that DDR disruption, only in the uterus, when insulin-IGF-1 signaling (IIS) is low, arrests oogenesis in the pachytene stage of meiosis I, in a FOXO/DAF-16 transcription factor (TF)-dependent manner. Without FOXO/DAF-16, germ cells of the IIS mutant escape the arrest to produce poor-quality oocytes, showing that the TF imposes strict quality control during low IIS. Activated FOXO/DAF-16 senses DDR perturbations during low IIS to lower ERK/MPK-1 signaling below a threshold to promote germ line arrest. Altogether, we elucidate a new surveillance role of activated FOXO/DAF-16 that ensures optimal germ cell quality and progeny fitness in response to somatic DNA damage.
... One possibility is the sterol hormone signaling pathway, which acts in somatic reproductive tissue to regulate glp-1(e2141) longevity. Decreasing the activity of the nuclear hormone receptor DAF-12, or its ligands dafachronic acids, abolishes the longevity of germline-less worms (Gerisch et al., 2001 ;Yamawaki et al., 2010 ). Interestingly, carbohydrate metabolism directly impacts the production of dafachronic acids as NADPH is required for the last step of dafachronic acid biosynthesis by DAF-9 (Motola et al., 2006 ;Penkov et al., 2015 ). ...
The transcriptional complex Mondo/Max-like, MML-1/MXL-2, acts as a convergent transcriptional regulatory output of multiple longevity pathways in Caenorhabditis elegans. These transcription factors coordinate nutrient sensing with carbohydrate and lipid metabolism across the evolutionary spectrum. While most studies have focused on the downstream outputs, little is known about the upstream inputs that regulate these transcription factors in a live organism. Here, we found that knockdown of various glucose metabolic enzymes decreases MML-1 localization in the nucleus and identified two hexokinase isozymes, hxk-1 and hxk-2, as the most vigorous regulators of MML-1 function. Upon hexokinase knockdown, MML-1 redistributes to mitochondria and lipid droplets (LD) and concomitantly, transcriptional targets are downregulated and germline longevity is abolished. Further, we found that hxk-1 regulates MML-1 through mitochondrial β-oxidation, while hxk-2 regulates MML-1 through modulating the pentose phosphate pathway (PPP) and its coordinated association with lipid droplets. Similarly, inhibition of the PPP rescues mammalian MondoA nuclear translocation and transcriptional function upon starvation. These studies reveal how metabolic signals and organellar communication regulate a key convergent metabolic transcription factor to promote longevity.
For the optimal survival of a species, an organism coordinates its reproductive decisions with the nutrient availability of its niche. Thus, nutrient-sensing pathways like insulin-IGF-1 signaling (IIS) play an important role in modulating cell division, oogenesis, and reproductive aging. Lowering of the IIS leads to the activation of the downstream FOXO transcription factor (TF) DAF-16 in Caenorhabditis elegans which promotes oocyte quality and delays reproductive aging. However, less is known about how the IIS axis responds to changes in cell cycle proteins, particularly in the somatic tissues. Here, we show a new aspect of the regulation of the germline by this nutrient-sensing axis. First, we show that the canonical G1-S cyclin, cyclin D/cyd-1, regulates reproductive aging from the uterine tissue of wild-type worms. Then, we show that knocking down cyd-1 in the uterine tissue of an IIS receptor mutant arrests oogenesis at the pachytene stage of meiosis-1 in a FOXO/DAF-16-dependent manner. We find that activated FOXO/DAF-16 destroys the somatic gonad tissues like the sheath cells, and transcriptionally prevents the spermatogenesis-to-oogenesis switch to orchestrate this arrest. Deleting FOXO/DAF-16 releases the arrest and restores the somatic gonad but leads to the production of poor-quality oocytes. Together, our study reveals the unrecognized cell non-autonomous interaction of CYD-1 and FOXO/DAF-16 in reproductive aging and the regulation of oogenesis.
Generating specific, robust protective responses to different bacteria is vital for animal survival. Here, we address the role of transforming growth factor β (TGF-β) member DBL-1 in regulating signature host defense responses in Caenorhabditis elegans to human opportunistic Gram-negative and Gram-positive pathogens. Canonical DBL-1 signaling is required to suppress avoidance behavior in response to Gram-negative, but not Gram-positive bacteria. We propose that in the absence of DBL-1, animals perceive some bacteria as more harmful. Animals activate DBL-1 pathway activity in response to Gram-negative bacteria and strongly repress it in response to select Gram-positive bacteria, demonstrating bacteria-responsive regulation of DBL-1 signaling. DBL-1 signaling differentially regulates expression of target innate immunity genes depending on the bacterial exposure. These findings highlight a central role for TGF-β in tailoring a suite of bacteria-specific host defenses.
In post-reproductive C. elegans, destructive somatic biomass repurposing supports production of yolk which, it was recently shown, is vented and can serve as a foodstuff for larval progeny. This is reminiscent of the suicidal reproductive effort (reproductive death) typical of semelparous organisms such as Pacific salmon. To explore the possibility that C. elegans exhibits reproductive death, we have compared sibling species pairs of the genera Caenorhabditis and Pristionchus with hermaphrodites and females. We report that yolk venting and constitutive, early pathology involving major anatomical changes occur only in hermaphrodites, which are also shorter lived. Moreover, only in hermaphrodites does germline removal suppress senescent pathology and markedly increase lifespan. This is consistent with the hypothesis that C. elegans exhibit reproductive death that is suppressed by germline ablation. If correct, this would imply a major difference in the ageing process between C. elegans and most higher organisms, and potentially explain the exceptional plasticity in C. elegans ageing.
The transcriptional complex Mondo/Max-like, MML-1/MXL-2, acts as a convergent transcriptional regulatory output of multiple longevity pathways in Caenorhabditis elegans. These transcription factors coordinate nutrient sensing with carbohydrate and lipid metabolism across the evolutionary spectrum. While most studies have focused on the downstream outputs, little is known about the upstream inputs that regulate these transcription factors in a live organism. Here, we found that knockdown of various glucose metabolic enzymes decreases MML-1 localization in the nucleus and identified two hexokinase isozymes, hxk-1 and hxk-2, as the most vigorous regulators of MML-1 function. Upon hexokinase knockdown, MML-1 redistributes to mitochondria and lipid droplets (LD) and concomitantly, transcriptional targets are downregulated and germline longevity is abolished. Further, we found that hxk-1 regulates MML-1 through mitochondrial b-oxidation, while hxk-2 regulates MML-1 through modulating the pentose phosphate pathway (PPP) and its coordinated association with lipid droplets. Similarly, inhibition of the PPP rescues mammalian MondoA nuclear translocation and transcriptional function upon starvation. These studies reveal how metabolic signals and organellar communication regulate a key convergent metabolic transcription factor to promote longevity.
Author Summary
The reproductive status and longevity of animals are strongly interlinked. Increasing age influences the reproductive capacities of most animals. However, little is known about how reproductive status might affect lifespan. Experiments in worms and flies have shown that removing cells that give rise to gametes, the “germ cells”, makes them live longer. We know very little about the genes and molecules that are involved in this process. In this study, we have identified a gene called tcer-1 that promotes the longevity of the roundworm Caenorhabditis elegans when its germ cells are removed. The gene tcer-1 codes for a protein, TCER-1, that is predicted to function as a “transcription elongation factor” (it allows the completion of RNA synthesis during the process of gene expression). Our experiments imply that when the germ cells of worms are removed, TCER-1 collaborates with a transcription factor called DAF-16/FOXO to express genes that contribute to increased longevity. DAF-16/FOXO can extend lifespan in response to other physiological cues besides loss of germ cells. However, TCER-1 specifically helps this widely used longevity protein to respond to signals that reflect the reproductive status. Counterparts of DAF-16/FOXO are known to control aging in other organisms, including humans, so the identification of TCER-1 may lead to a better understanding of the relationship between reproduction and aging in other species, too.
Fat metabolism, reproduction, and aging are intertwined regulatory axes; however, the mechanism by which they are coupled remains poorly understood. We found that germline stem cells (GSCs) actively modulate lipid hydrolysis in Caenorhabditis elegans, which in turn regulates longevity. GSC arrest promotes systemic lipolysis via induction of a specific fat lipase. Subsequently, fat mobilization is promoted and life span is prolonged. Constitutive expression of this lipase in fat storage tissue generates lean and long-lived animals. This lipase is a key factor in the lipid hydrolysis and increased longevity that are induced by decreased insulin signaling. These results suggest a link between C. elegans fat metabolism and longevity.
The daf-9 gene functions to integrate transforming growth factor-β and insulin-like signaling pathways to regulate Caenorhabditis elegans larval development. Mutations in daf-9 result in transient dauer-like larval arrest, abnormal reproductive development, molting defects and increased adult longevity. The phenotype is sterol-dependent, and dependent on the activity of DAF-12, a nuclear hormone receptor. Genetic tests show that daf-9 is upstream of daf-12 in the genetic pathways for larval development and adult longevity. daf-9 encodes a cytochrome P450 related to those involved in biosynthesis of steroid hormones in mammals. We propose that it specifies a step in the biosynthetic pathway for a DAF-12 ligand, which might be a steroid. The surprising cellular specificity of daf-9 expression (predominantly in two sensory neurons) supports a previously unrecognized role for these cells in neuroendocrine control of larval development, reproduction and life span.
daf-16 is a forkhead-type transcription factor, functioning downstream of insulin-like signals, and is known to be critical to the regulation of life span in Caenorhabditis elegans. Mammalian DAF-16 homologues include AFX, FKHR and FKHRL1, which contain a conserved forkhead domain and three putative phosphorylation sites for the Ser/Thr kinase Akt/protein kinase B (PKB), as well as for DAF-16. To assess the function of the homologues, we examined tissue distribution patterns of mRNAs for DAF-16 homologues in mice. In the embryos, expressions of AFX, FKHR and FKHRL1 mRNAs were complementary to each other and were highest in muscle, adipose tissue and embryonic liver. The characteristic expression pattern remained in the adult, except that signals of FKHRL1 became evident in more tissues, including the brain. In order to clarify whether each DAF-16 homologue had different target genes, we determined the consensus sequences for the binding of DAF-16 and the mouse homologues. The binding sequences for all four proteins shared a core sequence, TTGTTTAC, daf-16 family protein-binding element (DBE) binding protein. However, electrophoretic mobility shift assay showed that the binding affinity of DAF-16 homologues to the core sequence was stronger than that to the insulin-responsive element in the insulin-like growth factor binding protein-1 promoter region, which has been identified as a binding sequence for them. We identified one copy of the DBE upstream of the first exon of sod-3 by searching the genomic database of C. elegans. Taken together, DAF-16 homologues can fundamentally regulate the common target genes in insulin-responsive tissues and the specificity to target genes of each protein is partially determined by the differences in their expression patterns.
Many ectotherms, including C. elegans, have shorter life spans at high temperature than at low temperature. High temperature is generally thought to increase the "rate of living" simply by increasing chemical reaction rates. In this study, we questioned this view and asked whether the temperature dependence of life span is subject to active regulation.
We show that thermosensory neurons play a regulatory role in the temperature dependence of life span. Surprisingly, inhibiting the function of thermosensory neurons by mutation or laser ablation causes animals to have even shorter life spans at warm temperature. Thermosensory mutations shorten life span by decreasing expression of daf-9, a gene required for the synthesis of ligands that inhibit the DAF-12, a nuclear hormone receptor. The short life span of thermosensory mutants at warm temperature is completely suppressed by a daf-12(-) mutation.
Our data suggest that thermosensory neurons affect life span at warm temperature by changing the activity of a steroid-signaling pathway that affects longevity. We propose that this thermosensory system allows C. elegans to reduce the effect that warm temperature would otherwise have on processes that affect aging, something that warm-blooded animals do by controlling temperature itself.
In the wild-type C. elegans germ line there are both mitotic and meiotic germ cells. Mutations in glp-1 cause germ cells that would normally divide mitotically to enter meiosis. This mutant phenotype mimics the effect of killing the distal tip cell, a somatic cell that interacts with the germ line to regulate the mitotic/meiotic decision. In addition, wild-type glp-1 product is required maternally for embryogenesis. Temperature-shift experiments indicate that the temporal requirement for glp-1 activity in the germ line is the same as that for distal tip cell regulation. Mosaic analyses suggest that glp-1 is produced in the germ line. We propose that glp-1 acts as part of the receiving mechanism in the interaction between the distal tip cell and germ line.
Methods are described for the isolation, complementation and mapping of mutants of Caenorhabditis elegans, a small free-living nematode worm. About 300 EMS-induced mutants affecting behavior and morphology have been characterized and about one hundred genes have been defined. Mutations in 77 of these alter the movement of the animal. Estimates of the induced mutation frequency of both the visible mutants and X chromosome lethals suggests that, just as in Drosophila, the genetic units in C. elegans are large.
We have found that mutations in the gene daf-2 can cause fertile, active, adult Caenorhabditis elegans hermaphrodites to live more than twice as long as wild type. This lifespan extension, the largest yet reported in any organism, requires the activity of a second gene, daf-16. Both genes also regulate formation of the dauer larva, a developmentally arrested larval form that is induced by crowding and starvation and is very long-lived. Our findings raise the possibility that the longevity of the dauer is not simply a consequence of its arrested growth, but instead results from a regulated lifespan extension mechanism that can be uncoupled from other aspects of dauer formation. daf-2 and daf-16 provide entry points into understanding how lifespan can be extended.
![Overexpression of DAF-9/CYP450 in the XXX cells or hypodermis can extend the lifespan of germ cell ( 2 ) ; somatic gonad ( 2 ) animals. A GFP-tagged DAF-9/CYP450 protein, which catalyzes the final step of the synthesis of dafachronic acids, was overexpressed under the control of various promoters using multi-copy transgene arrays. Use of a daf-9(e1406) mutant background limited overexpression to specific tissue types. (A) Removal of the somatic gonad plus the germ cells of animals expressing daf-9::GFP under the control of the daf-9 promoter extended lifespan. Somatic-gonad plus germ cell removal also extended the lifespan of animals expressing daf-9::GFP in the XXX cells using the sdf-9 promoter (B) and in animals expressing daf-9::GFP in the hypodermis using the dpy-7 promoter (C). [However, expression of DAF-9::GFP in the hypodermis of germine-deficient animals lacking the somatic gonad using the col-12 promoter did not extend lifespan (Table S2). GFP fluorescence was visible in these animals, and the construct rescued the constitutive dauer formation phenotype of daf-9(e1406) animals [15] suggesting DAF-9/CYP450 was active in these transgenic animals. It is possible that the level of expression was not sufficient to rescue the longevity of these animals.] (D) Somatic gonad plus germ cell removal also extended the lifespan of animals expressing daf-9::GFP under the control of the che-2 promoter, which drives expression in sensory neurons, which do not normally express daf-9 /CYP450. Details including means and p values for all experiments are listed in Table S2. doi:10.1371/journal.pbio.1000468.g002](https://www.researchgate.net/profile/Mark-Mccormick-10/publication/46170873/figure/fig2/AS:307337362460672@1450286345116/Overexpression-of-DAF-9-CYP450-in-the-XXX-cells-or-hypodermis-can-extend-the-lifespan-of_Q320.jpg)
