Dietary regulation of hypodermal polyploidization in C. elegans

Dietary cobalt oxide nanoparticles alleviate aging through activation of mitochondrial UPR in Caenorhabditis elegans

Mitochondrial unfolded protein response (UPRmt), which is a mitochondrial proteostasis pathway, orchestrates an adaptive reprogramming for metabolism homeostasis and organismal longevity. Similar to other defense systems, compromised UPRmt is a feature of several age-related diseases. Here we report that dimercapto succinic acid (DMSA)-modified cobalt oxide nanoparticles (Co3O4 NPs), which have received wide-spread attention in biomedical fields, is a promising UPRmt activator and, more importantly, provides a gate for extending healthy lifespan. Methods: UPRmt activation by Co3O4 NPs was tested in transgenetic Caenorhabditis elegans (C. elegans) specifically expressing UPRmt reporter Phsp-6::GFP, and the underlying mechanism was further validated by mitochondrial morphology, mtDNA/nDNA, metabolism-related genes' expression, mitonuclear protein imbalance, oyxgen assumption and ATP level in C. elegans. Then therapeutic response aganist senescence was monitored by lifespan analysis, lipofusin contents, MDA contents, Fe accumulation, pharyngeal locomotion performance as well as athletic ability (head thrashes and body bends) at different developmental stages of C. elegans. RNAi towards ubl-5 or atfs-1 in UPRmt pathway was applied to clarify the role of UPRmt in Co3O4 NPs -mediated anti-aging effects. Finally, the effect of Co3O4 NPs on mitochondrial homeostasis and D-galactose-induced cell viability decline in mammalian cells were studied. Results: Co3O4 NPs was revealed as a bona fide activator of the UPRmt signaling pathway, through fine-tuning mitochondrial dynamics and inducing a stoichiometric imbalance between OXPHOS subunits encoded by mitochondrial DNA (mtDNA) and nuclear DNA (nDNA) at early life stage of C. elegans. Phenotypically, Co3O4 NPs treatment protect C. elegans from external stresses. More importantly, dietary low level of Co3O4 NPs effectively extend lifespan and alleviate aging-related physiological and functional decline of worms, demonstrating its potential roles in delaying aging. While the protective effect exerted by Co3O4 NPs was compromised in line with atfs-1 or ubl-5 RNAi treatment. Further studies verified the conservation of Co3O4 NPs in activating UPRmt and exerting protective effects in mammalian cells. Conclusions: The results reveal beneficial effects of Co3O4 NPs on mitochondrial metabolic control, thus presenting their potential efficacy in anti-aging care.

Lacticaseibacillus rhamnosus Probio-M9 extends the lifespan of Caenorhabditis elegans

Probiotics have been characterized as useful for maintaining the balance of host gut flora and conferring health effects, but few studies have focused on their potential for delaying aging in the host. Here we show that Lacticaseibacillus rhamnosus Probio-M9 (Probio-M9), a healthy breast milk probiotic, enhances the locomotor ability and slows the decline in muscle function of the model organism Caenorhabditis elegans. Live Probio-M9 significantly extends the lifespan of C. elegans in a dietary restriction-independent manner. By screening various aging-related mutants of C. elegans, we find that Probio-M9 extends lifespan via p38 cascade and daf-2 signaling pathways, independent on daf-16 but dependent on skn-1. Probio-M9 protects and repairs damaged mitochondria by activating mitochondrial unfolded protein response. The significant increase of amino acids, sphingolipid, galactose and fatty acids in bacterial metabolites might be involved in extending the lifespan of C. elegans. We reveal that Probio-M9 as a dietary supplementation had the potential to delay aging in C. elegans and also provide new methods and insights for further analyzing probiotics in improving host health and delaying the occurrence of age-related chronic diseases.

Exploring of probiotic potential vaginal Lactobacillus isolates from healthy women against Gardnerella vaginalis and Caenorhabditis elegans model testing

AIM

Lactobacillus species are the dominant microorganisms in the vaginal microbiota of healthy women and play an important role in the defense against pathogens. This study aimed to evaluate probiotic potential of Lactiplantibacillus plantarum strain P1 isolated from healthy woman's vaginal discharge for its further utilization as a promising candidate strain in the treatment of bacterial vaginosis caused by Gardnerella vaginalis.

METHODS AND RESULTS

Ten lactobacilli strains from a woman's vaginal discharge were evaluated for their probiotic potential, including growth capacity at different pH levels (pH3.5~4.5), acid production, hydrogen peroxide production capacity, antibacterial activity, susceptibility to antibiotics. Moreover In vitro safety assay hemolytic activity and mutagenicity were investigated for safety assessment. In vivo Caenorhabditis elegans infection model was used to investigate the anti-infection effect of selected isolates. We found that lactobacilli strain P1 showed strong growth ability in low acid environment, produced acid, hydrogen peroxide, had the strongest antibacterial activity against G. vaginalis and was highly susceptible to the tested antibiotics. When assayed for the safety, strain P1 showed no hemolytic activity and had no effect of mutagenicity. Moreover, P1 significantly increased the lifespan of C. elegans against G. vaginalis infection. Combined with the results of 16S rRNA gene sequencing, morphological and physiological characteristic, the strain was identified as Lactiplantibacillus plantarum.

CONCLUSION

Lactiplantibacillus plantarum strain P1 proves to be a promising candidate strain in the treatment of bacterial vaginosis caused by G. vaginalis.

SIGNIFICANCE AND IMPACT OF THE STUDY

Conventional antibiotic therapy for bacterial vaginosis has led to the accelerated process of bacterial drug resistance. Probiotics are potentially an alternative method for bacterial vaginosis therapy. This finding provides bacterial resources for keeping pathogens away from the vagina. We believe L. plantarum P1 may be used as vaginal probiotics and be useful to prevent or treat bacterial vaginitis.

SMA-10 Is a Non-Canonical Member of the TGF-β Sma/Mab Pathway and Immunity Regulator via the DAF-2 Insulin Receptor in Caenorhabditis elegans

Transforming growth factor β (TGF-β) signalling pathways are highly conserved across metazoa and play essential roles not only during development but also in adult tissue maintenance. Alterations of these pathways usually result in a plethora of pathologies. In the nematode Caenorhabditis elegans, the TGF-β Sma/Mab (small/male abnormal) pathway regulates various worm phenotypes such as body size, immune response, ageing, matricide and reproductive span. SMA-10 has been described as a positive modulator of worm body size through the TGF-β Sma/Mab pathway. To better understand if SMA-10 is a core component of the pathway, we use gene epistatic analysis to assess the contribution of SMA-10 to various phenotypes regulated by TGF-β Sma/Mab. We confirm that SMA-10 controls body size and find that it also affects the matricide and reproductive span of the nematodes. However, neither male tail formation (previously reported) nor ageing appeared altered. Lastly, although null sma-10 worms are more susceptible to Pseudomonas aeruginosa infections than wild-types, this response does not depend on TGF-β Sma/Mab but on the insulin receptor DAF-2. We also show that the expression of sma-10 in either hypodermis or intestine fully rescues the wild-type immune response. Our results contribute to understanding the role of SMA-10 as a context-dependent component of TGF-β Sma/Mab, and reveal a function of SMA-10 in immunity in association to the Insulin/insulin-like growth factor signalling (IIS) pathway.

Metolazone upregulates mitochondrial chaperones and extends lifespan in Caenorhabditis elegans

Accumulating studies have argued that the mitochondrial unfolded protein response (UPR^mt) is a mitochondrial stress response that promotes longevity in model organisms. In the present study, we screened an off-patent drug library to identify compounds that activate UPR^mt using a mitochondrial chaperone hsp-6::GFP reporter system in Caenorhabditis elegans. Metolazone, a diuretic primarily used to treat congestive heart failure and high blood pressure, was identified as a prominent hit as it upregulated hsp-6::GFP and not the endoplasmic reticulum chaperone hsp-4::GFP. Furthermore, metolazone specifically induced the expression of mitochondrial chaperones in the HeLa cell line. Metolazone also extended the lifespan of worms in a atfs-1 and ubl-5-dependent manner. Notably, metolazone failed to increase lifespan in worms with knocked-down nkcc-1. These results suggested that metolazone activates the UPR^mt across species and prolongs the lifespan of C. elegans.

Nutrient Sensing and Response Drive Developmental Progression in Caenorhabditis elegans

In response to nutrient limitation, many animals, including Caenorhabditis elegans, slow or arrest their development. This process requires mechanisms that sense essential nutrients and induce appropriate responses. When faced with nutrient limitation, C. elegans can induce both short and long-term survival strategies, including larval arrest, decreased developmental rate, and dauer formation. To select the most advantageous strategy, information from many different sensors must be integrated into signaling pathways, including target of rapamycin (TOR) and insulin, that regulate developmental progression. Here, how nutrient information is sensed and integrated into developmental decisions that determine developmental rate and progression in C. elegans is reviewed.

Developmental Control of the Cell Cycle: Insights from Caenorhabditis elegans

During animal development, a single fertilized egg forms a complete organism with tens to trillions of cells that encompass a large variety of cell types. Cell cycle regulation is therefore at the center of development and needs to be carried out in close coordination with cell differentiation, migration, and death, as well as tissue formation, morphogenesis, and homeostasis. The timing and frequency of cell divisions are controlled by complex combinations of external and cell-intrinsic signals that vary throughout development. Insight into how such controls determine in vivo cell division patterns has come from studies in various genetic model systems. The nematode Caenorhabditis elegans has only about 1000 somatic cells and approximately twice as many germ cells in the adult hermaphrodite. Despite the relatively small number of cells, C. elegans has diverse tissues, including intestine, nerves, striated and smooth muscle, and skin. C. elegans is unique as a model organism for studies of the cell cycle because the somatic cell lineage is invariant. Somatic cells divide at set times during development to produce daughter cells that adopt reproducible developmental fates. Studies in C. elegans have allowed the identification of conserved cell cycle regulators and provided insights into how cell cycle regulation varies between tissues. In this review, we focus on the regulation of the cell cycle in the context of C. elegans development, with reference to other systems, with the goal of better understanding how cell cycle regulation is linked to animal development in general.

Clostridium butyricum MIYAIRI 588 Increases the Lifespan and Multiple-Stress Resistance of Caenorhabditis elegans

Clostridium butyricum MIYAIRI 588 (CBM 588), one of the probiotic bacterial strains used for humans and domestic animals, has been reported to exert a variety of beneficial health effects. The effect of this probiotic on lifespan, however, is unknown. In the present study, we investigated the effect of CBM 588 on lifespan and multiple-stress resistance using Caenorhabditis elegans as a model animal. When adult C. elegans were fed a standard diet of Escherichia coli OP50 or CBM 588, the lifespan of the animals fed CBM 588 was significantly longer than that of animals fed OP50. In addition, the animals fed CBM588 exhibited higher locomotion at every age tested. Moreover, the worms fed CBM 588 were more resistant to certain stressors, including infections with pathogenic bacteria, UV irradiation, and the metal stressor Cu²⁺. CBM 588 failed to extend the lifespan of the daf-2/insulin-like receptor, daf-16/FOXO and skn-1/Nrf2 mutants. In conclusion, CBM 588 extends the lifespan of C. elegans probably through regulation of the insulin/IGF-1 signaling (IIS) pathway and the Nrf2 transcription factor, and CBM 588 improves resistance to several stressors in C. elegans.

Dramatic evolution of body length due to postembryonic changes in cell size in a newly discovered close relative of Caenorhabditis elegans

Understanding morphological diversity-and morphological constraint-has been a central question in evolutionary biology since its inception. Nematodes of the genus Caenorhabditis, which contains the well-studied model organism C. elegans, display remarkable morphological consistency in the face of extensive genetic divergence. Here, we provide a description of the broad developmental patterns of a newly discovered species, C. sp. 34, which was isolated from fresh figs in Okinawa and which is among the closest known relatives of C. elegans. C. sp. 34 displays an extremely large body size; it can grow to be nearly twice as long as C. elegans and all other known members of the genus. Observations of the timing of developmental milestones reveal that C. sp. 34 develops about twice as slowly as C. elegans. Measurements of embryonic and larval size show that the size difference between C. sp. 34 and C. elegans is largely due to postembryonic events, particularly during the transition from larval to adult stages. This difference in size is not attributable to differences in germ line chromosome number or the number of somatic cells. The overall difference in body size is therefore largely attributable to changes in cell size via increased cytoplasmic volume. Because of its close relationship to C. elegans, the distinctness of C. sp. 34 provides an ideal system for the detailed analysis of evolutionary diversification. The context of over 40 years of C. elegans developmental genetics also reveals clues into how natural selection and developmental constraint act jointly to promote patterns of morphological stasis and divergence in this group.

Caenorhabditis elegans respond to high-glucose diets through a network of stress-responsive transcription factors

High-glycemic-index diets, as well as a sedentary lifestyle are considered as determinant factors for the development of obesity, type 2 diabetes, and cardiovascular diseases in humans. These diets have been shown to shorten the life span of C. elegans in a manner that is dependent on insulin signaling, but the participation of other signaling pathways have not been addressed. In this study, we have determined that worms fed with high-glucose diets show alterations in glucose content and uptake, triglyceride content, body size, number of eggs laid, egg-laying defects, and signs of oxidative stress and accelerated aging. Additionally, we analyzed the participation of different key regulators of carbohydrate and lipid metabolism, oxidative stress and longevity such as SKN-1/NRF2, HIF-1/HIF1α, SBP-1/SREBP, CRH-1/CREB, CEP-1/p53, and DAF-16/FOXO, in the reduction of lifespan in glucose-fed worms.

ChIP and Chips: Introducing the WormPharm for correlative studies employing pharmacology and genome-wide analyses in C. elegans

We present the WormPharm, an automated microfluidic platform that utilizes an axenic medium to culture C. elegans. The WormPharm is capable of sustaining C. elegans for extended periods, while recording worm development and growth with high temporal resolution ranging from seconds to minutes over several days to months. We demonstrate the utility of the device to monitor C. elegans growth in the presence of varying doses of nicotine and alcohol. Furthermore, we show that C. elegans cultured in the WormPharm are amendable for high-throughput genomic assays, i.e. chromatin-immunoprecipitation followed by next generation sequencing, and confirm that nematodes grown in monoxenic and axenic cultures exhibit genetic modifications that correlate with observed phenotypes. The WormPharm is a powerful tool for analyzing the effects of chemical, nutritional and environmental variations on organism level responses in conjunction with genome-wide changes in C. elegans.

Receptor Guanylyl Cyclases in Sensory Processing

Invertebrate models have generated many new insights into transmembrane signaling by cell-surface receptors. This review focuses on receptor guanylyl cyclases (rGCs) and describes recent advances in understanding their roles in sensory processing in the nematode, Caenorhabditis elegans. A complete analysis of the C. elegans genome elucidated 27 rGCs, an unusually large number compared with mammalian genomes, which encode 7 rGCs. Most C. elegans rGCs are expressed in sensory neurons and play roles in sensory processing, including gustation, thermosensation, olfaction, and phototransduction, among others. Recent studies have found that by producing a second messenger, guanosine 3',5'-cyclic monophosphate, some rGCs act as direct sensor molecules for ions and temperatures, while others relay signals from G protein-coupled receptors. Interestingly, genetic and biochemical analyses of rGCs provide the first example of an obligate heterodimeric rGC. Based on recent structural studies of rGCs in mammals and other organisms, molecular mechanisms underlying activation of rGCs are also discussed in this review.

Life history trait analysis of the entomopathogenic nematode Steinernema feltiae provides the basis for prediction of dauer juvenile yields in monoxenic liquid culture

Entomopathogenic nematodes (Steinernema spp.) are used in integrated pest management to control insect pests in cryptic environments. The nematodes are mass produced in monoxenic liquid culture with their symbiotic bacteria Xenorhabdus spp. For a better understanding of nematode population dynamics, the life history traits (LHTs) of the entomopathogenic nematode Steinernema feltiae were assessed at 25 °C by observing single pairs of male and female nematodes using a hanging drop technique. To investigate the influence of different food supplies on nematode reproduction, the LHTs were assessed with a daily supply of 5 ×, 10 × and 20 × 10(9) cells ml(-1) of the nematode's bacterial symbiont Xenorhabdus bovienii in semi-solid nematode growth gelrite (NGG) medium. Increasing bacterial density had a significant positive influence on the average number of offspring produced, which ranged from 359 to 813 per female. The intrinsic rate of natural increase r m, which ranges from 1.10 to 1.19 day(-1), was neither influenced by the bacterial density, nor was the mean generation time T (5.12-5.25 days) and population doubling time (PDT) (0.64-0.59 days). The average lifespan of reproductive females, which ranged from 6.7 to 7.3 days, was positively correlated with bacterial density. A positive correlation between female body volume and bacterial density was recorded (R = 0.67) as well as a significant positive correlation between female body size and offspring production (R = 0.89) in hanging drops. Whether these data can be used to predict nematode yields in liquid culture was tested. The total female body volume calculated as the average female body volume × total number of parental females per millilitre 3 days after nematode inoculation was positively correlated (R = 0.72) with nematode yields. The total female body volume on process day 3 is thus a good indicator for the estimation of nematode yield at the end of the process (12-15 days post dauer juvenile (DJ) inoculation) in both Erlenmeyer flasks and bioreactors. With a mean deviation of 9467 DJs ml(-1), the error resembles approximately 5 % of the final DJ yields.

miR-58 family and TGF-β pathways regulate each other in Caenorhabditis elegans

Despite the fact that microRNAs (miRNAs) modulate the expression of around 60% of protein-coding genes, it is often hard to elucidate their precise role and target genes. Studying miRNA families as opposed to single miRNAs alone increases our chances of observing not only mutant phenotypes but also changes in the expression of target genes. Here we ask whether the TGF-β signalling pathways, which control many animal processes, might be modulated by miRNAs in Caenorhabditis elegans. Using a mutant for four members of the mir-58 family, we show that both TGF-β Sma/Mab (controlling body size) and TGF-β Dauer (regulating dauer, a stress-resistant larval stage) are upregulated. Thus, mir-58 family directly inhibits the expression of dbl-1 (ligand), daf-1, daf-4 and sma-6 (receptors) of TGF-β pathways. Epistasis experiments reveal that whereas the small body phenotype of the mir-58 family mutant must invoke unknown targets independent from TGF-β Sma/Mab, its dauer defectiveness can be rescued by DAF-1 depletion. Additionally, we found a negative feedback loop between TGF-β Sma/Mab and mir-58 and the related mir-80. Our results suggest that the interaction between mir-58 family and TGF-β genes is key on decisions about animal growth and stress resistance in C. elegans and perhaps other organisms.

The Importance of cGMP Signaling in Sensory Cilia for Body Size Regulation in Caenorhabditis elegans

The body size of Caenorhabditis elegans is thought to be controlled by sensory inputs because many mutants with sensory cilium structure defects exhibit small body size. The EGL-4 cGMP-dependent protein kinase acts in sensory neurons to reduce body size when animals fail to perceive sensory signals. In addition to body size control, EGL-4 regulates various other behavioral and developmental pathways, including those involved in the regulation of egg laying and chemotaxis behavior. Here we have identified gcy-12, which encodes a receptor-type guanylyl cyclase, as a gene involved in the sensory regulation of body size. Analyses with GFP fusion constructs showed that gcy-12 is expressed in several sensory neurons and localizes to sensory cilia. Genetic analyses indicated that GCY-12 acts upstream of EGL-4 in body size control but does not affect other EGL-4 functions. Our studies indicate that the function of the GCY-12 guanylyl cyclase is to provide cGMP to the EGL-4 cGMP-dependent kinase only for limited tasks including body size regulation. We also found that the PDE-2 cyclic nucleotide phosphodiesterase negatively regulates EGL-4 in controlling body size. Thus, the cGMP level is precisely controlled by GCY-12 and PDE-2 to determine body size through EGL-4, and the defects in the sensory cilium structure may disturb the balanced control of the cGMP level. The large number of guanylyl cyclases encoded in the C. elegans genome suggests that EGL-4 exerts pleiotropic effects by partnering with different guanylyl cyclases for different downstream functions.

Life history trait analysis of the entomopathogenic nematode Steinernema riobrave

Life history traits (LHT) of Steinernema riobrave strain Sr 7-12 and Sr HYB19 were assessed at 25°C in monoxenic culture using a hanging drop technique. The LHT were studied with 5 × 109, 10 × 109 and 20 × 109 cells ml−1 of Xenorhabdus cabanillasii in semi-solid Nematode Growth Gelrite. Increased X. cabanillasii densities had a significant positive influence on offspring production on both Sr 7-12 and the hybrid Sr HYB19. At the higher bacterial food density, the total fertility rate (TFR) per female of Sr 7-12 was 2022 offspring and the net reproductive rate () reached 1904 offspring. Similarly, for Sr HYB19, the TFR per female was 2434 and was 1903. The percentage offspring produced via intra-uterine development (endotokia matricida) was relatively higher at 5 × 109 bacterial cells ml−1 than at higher bacterial density, with 64% and 66% of the total offspring produced by Sr 7-12 and Sr HYB19, respectively. A positive correlation () was recorded for offspring production and bacterial food density and for female body volume with bacterial density (). Female nematodes survived longer at higher bacterial food density; however, females of both strains could not survive longer than 7.8 days, beginning from hatching and always ending 1 day after initiation of endotokia matricida. Based on LHT results, there is a potential to maximise yield of dauer juveniles in liquid culture through increasing bacterial food density.

Identifying evolutionarily conserved genes in the dietary restriction response using bioinformatics and subsequent testing in Caenorhabditis elegans

Dietary restriction (DR) increases life span, health span and resistance to stress in a wide range of organisms. Work from a large number of laboratories has revealed evolutionarily conserved mechanisms that mediate the DR response. Here, we analyzed the genome-wide gene expression profiles of Caenorhabditis elegans under DR versus ad libitum conditions. Using the Ortho2ExpressMatrix tool, we searched for C. elegans orthologs of mouse genes that have been shown to be differentially expressed under DR conditions in nearly 600 experiments. Based on our bioinformatic approaches, we obtained 189 DR-responsive genes, and 45 of these are highly conserved from worm to man. Subsequent testing of sixteen genes that are up-regulated under DR identified eight genes that abolish the DR-induced resistance to heat stress in C. elegans. Further analyses revealed that fkb-4, dod-22 and ikb-1 genes also abolish increased life span in response to DR. The identified genes that are necessary for the DR response are sensitive to certain stress signals such as metabolic perturbances (dod-22, fkb-4 and nhr-85), DNA damage (ikb-1), heat shock (hsp-12.6) and cancer-like overgrowth (prk-2 and tsp-15). We propose that most of the DR-responsive genes identified are components of the recently discovered cellular surveillance-activated detoxification and defenses pathway, which is, among others, important for the survival of organisms in times of food deprivation.

The control of cell growth and body size in Caenorhabditis elegans

One of the most important ways in which animal species vary is in their size. Individuals of the largest animal ever thought to have lived, the blue whale (Balaenoptera musculus), can reach a weight of 190 t and a length of over 30 m. At the other extreme, among the smallest multicellular animals are males of the parasitic wasp, Dicopomorpha echmepterygis, which even as adults are just 140 μm in length. In terms of volume, these species differ by more than 14 orders of magnitude. Since size has such profound effects on an organism's ecology, anatomy and physiology, an important task for evolutionary biology and ecology is to account for why organisms grow to their characteristic sizes. Equally, a full description of an organism's development must include an explanation of how its growth and body size are regulated. Here I review research on how these processes are controlled in the nematode, Caenorhabditis elegans. Analyses of small and long mutants have revealed that in the worm, DBL-1, a ligand in the TGFβ superfamily family, promotes growth in a dose-dependent manner. DBL-1 signaling affects body size by stimulating the growth of syncytial hypodermal cells rather than controlling cell division. Signals from chemosensory neurons and from the gonad also modulate body size, in part, independently of DBL-1-mediated signaling. Organismal size and morphology is heavily influenced by the cuticle, which acts as the exoskeleton. Finally, I summarize research on several genes that appear to regulate body size by cell autonomously regulating cell growth throughout the worm.

Phenotypic plasticity in nematodes: Evolutionary and ecological significance

Model systems, including C. elegans, have been successfully studied to understand the genetic control of development. A genotype's phenotype determines its evolutionary fitness in natural environments, which are typically harsh, heterogeneous and dynamic. Phenotypic plasticity, the process by which one genome can produce different phenotypes in response to the environment, allows genotypes to better match their phenotype to their environment. Phenotypic plasticity is rife among nematodes, seen both as differences among life-cycles stages, perhaps best exemplified by parasitic nematodes, as well as developmental choices, such as shown by the C. elegans dauer/non-dauer developmental choice. Understanding the genetic basis of phenotypically plastic traits will probably explain the function of many genes whose function still remains unclear. Understanding the adaptive benefits of phenotypically plastic traits requires that we understand how plasticity differs among genotypes, and the effects of this in diverse, different environments.

Sex differences in body composition, fat storage, and gene expression profile in Caenorhabditis elegans in response to dietary restriction

The metabolic and health-promoting effects of dietary restriction (DR) have been extensively studied in several species. The response to DR with respect to sex is essentially unknown. To address this question, we used the model organism Caenorhabditis elegans to analyze body composition and gene expression in males and hermaphrodites in response to DR. Unexpectedly, DR increased the fat-to-fat-free mass ratio and enlarged lipid droplets in both sexes to a similar extent. These effects were linked to a downregulation of the lipase-like 5 (lipl-5) gene in both sexes at two developmental stages. By contrast, the reductions in body size, protein content, and total RNA content in response to DR were more pronounced in hermaphrodites than in males. Functional enrichment analysis of gene expression data showed a DR-induced downregulation of several embryogenesis-associated genes concomitant with an ongoing expression of sperm-associated genes in hermaphrodites. In conclusion, DR increases fat stores in both sexes of C. elegans in the form of large and possibly lipolysis-resistant lipid droplets and markedly alters the reproductive program in hermaphrodites but not in males.

Dietary restriction during development enlarges intestinal and hypodermal lipid droplets in Caenorhabditis elegans

Dietary restriction (DR) extends lifespan in man species and modulates evolutionary conserved signalling and metabolic pathways. Most of these studies were done in adult animals. Here we investigated fat phenotypes of C. elegans larvae and adults which were exposed to DR during development. This approach was named "developmental-DR" (dDR). Moderate as well as stringent dDR increased the triglyceride to protein ratio in L4 larvae and adult worms. This alteration was accompanied by a marked expansion of intestinal and hypodermal lipid droplets. In comparison to ad libitum condition, the relative proportion of fat stored in large lipid droplets (>50 µm(3)) was increased by a factor of about 5 to 6 in larvae exposed to dDR. Microarray-based expression profiling identified several dDR-regulated genes of lipolysis and lipogenesis which may contribute to the observed fat phenotypes. In conclusion, dDR increases the triglyceride to protein ratio, enlarges lipid droplets and alters the expression of genes functioning in lipid metabolism in C. elegans. These changes might be an effective adaptation to conserve fat stores in animals subjected to limiting food supply during development.

The Caenorhabditis elegans epidermis as a model skin. I: development, patterning, and growth

The skin of the nematode Caenorhabditis elegans is composed of a simple epidermal epithelium and overlying cuticle. The skin encloses the animal and plays central roles in body morphology and physiology; its simplicity and accessibility make it a tractable genetic model for several aspects of skin biology. Epidermal precursors are specified by a hierarchy of transcriptional regulators. Epidermal cells form on the dorsal surface of the embryo and differentiate to form the epidermal primordium, which then spreads out in a process of epiboly to enclose internal tissues. Subsequent elongation of the embryo into a vermiform larva is driven by cell shape changes and cell fusions in the epidermis. Most epidermal cells fuse in mid-embryogenesis to form a small number of multinucleate syncytia. During mid-embryogenesis the epidermis also becomes intimately associated with underlying muscles, performing a tendon-like role in transmitting muscle force. Post-embryonic development of the epidermis involves growth by addition of new cells to the syncytia from stem cell-like epidermal seam cells and by an increase in cell size driven by endoreplication of the chromosomes in epidermal nuclei.

Control of body size in C. elegans dependent on food and insulin/IGF-1 signal

The body size of an organism is governed by genetic and environmental factors. As an environmental factor, food appears to be the most important for body size control in animals. C. elegans worms are usually grown on an E. coli strain OP50. We show that the wild-type worms fed on another E. coli strain HB101 grow 1.6 times as large as those fed on OP50. The regression line representing the relationship between the sizes of worms grown on each food for over 30 mutants was drawn, indicating that small mutants tend to be more affected by the change in food. Mutants for the DAF-2 insulin/IGF-1 receptor and downstream SGK-1, a homolog of the serum- and glucocorticoid-inducible kinase, grow less or little larger on HB101, indicating control of body size by these factors. Results on the suppression of mutations in these factors by a mutation in the DAF-16/FOXO transcription factor indicate both DAF-16-dependent and DAF-16-independent control. Furthermore, we show that the food-dependent body size change is because of a change in cell size that is closely related to the protein content per cell.

A novel zf-MYND protein, CHB-3, mediates guanylyl cyclase localization to sensory cilia and controls body size of Caenorhabditis elegans

Cilia are important sensory organelles, which are thought to be essential regulators of numerous signaling pathways. In Caenorhabditis elegans, defects in sensory cilium formation result in a small-body phenotype, suggesting the role of sensory cilia in body size determination. Previous analyses suggest that lack of normal cilia causes the small-body phenotype through the activation of a signaling pathway which consists of the EGL-4 cGMP-dependent protein kinase and the GCY-12 receptor-type guanylyl cyclase. By genetic suppressor screening of the small-body phenotype of a cilium defective mutant, we identified a chb-3 gene. Genetic analyses placed chb-3 in the same pathway as egl-4 and gcy-12 and upstream of egl-4. chb-3 encodes a novel protein, with a zf-MYND motif and ankyrin repeats, that is highly conserved from worm to human. In chb-3 mutants, GCY-12 guanylyl cyclase visualized by tagged GFP (GCY-12::GFP) fails to localize to sensory cilia properly and accumulates in cell bodies. Our analyses suggest that decreased GCY-12 levels in the cilia of chb-3 mutants may cause the suppression of the small-body phenotype of a cilium defective mutant. By observing the transport of GCY-12::GFP particles along the dendrites to the cilia in sensory neurons, we found that the velocities and the frequencies of the particle movement are decreased in chb-3 mutant animals. How membrane proteins are trafficked to cilia has been the focus of extensive studies in vertebrates and invertebrates, although only a few of the relevant proteins have been identified. Our study defines a new regulator, CHB-3, in the trafficking process and also shows the importance of ciliary targeting of the signaling molecule, GCY-12, in sensory-dependent body size regulation in C. elegans. Given that CHB-3 is highly conserved in mammal, a similar system may be used in the trafficking of signaling proteins to the cilia of other species.

Caenorhabditis elegans is a 1–2 mm long nematode. Its body size is controlled by sensory inputs; some mutants with defects in sensory perception grow into small size (20%–30% decrease in body volume), although the animals seem to feed normally. The EGL-4 cGMP-dependent protein kinase and the GCY-12 guanylyl cyclase act in sensory neurons to control body size downstream of sensory inputs. GCY-12 is localized to cilia, antenna-like cellular structures of sensory neurons. In the cilia, a number of signaling molecules are localized. Dysfunction of cilia is known to cause several human disorders such as Bardet-Biedl syndrome, illustrating the importance of these organelles. In this study, we identified a novel protein, CHB-3, involved in sensory-dependent body size regulation. Our analyses suggest that CHB-3 protein regulates the trafficking of GCY-12 from the cell bodies to the cilia. Without CHB-3 protein, GCY-12 fails to localize to cilia and body size is not controlled properly. Thus, the cilia are a special place for sensory information processing in body size regulation. Our analyses identified CHB-3 as a novel trafficking regulator of ciliary protein(s).

Life cycle and population growth rate of Caenorhabditis elegans studied by a new method

Background

The free-living nematode Caenorhabditis elegans is the predominant model organism in biological research, being used by a huge number of laboratories worldwide. Many researchers have evaluated life-history traits of C. elegans in investigations covering quite different aspects such as ecotoxicology, inbreeding depression and heterosis, dietary restriction/supplement, mutations, and ageing. Such traits include juvenile growth rates, age at sexual maturity, adult body size, age-specific fecundity/mortality, total reproduction, mean and maximum lifespan, and intrinsic population growth rates. However, we found that in life-cycle experiments care is needed regarding protocol design. Here, we test a recently developed method that overcomes some problems associated with traditional cultivation techniques. In this fast and yet precise approach, single individuals are maintained within hanging drops of semi-fluid culture medium, allowing the simultaneous investigation of various life-history traits at any desired degree of accuracy. Here, the life cycles of wild-type C. elegans strains N2 (Bristol, UK) and MY6 (Münster, Germany) were compared at 20°C with 5 × 10⁹ Escherichia coli ml^-1 as food source.

Results

High-resolution life tables and fecundity schedules of the two strains are presented. Though isolated 700 km and 60 years apart from each other, the two strains barely differed in life-cycle parameters. For strain N2 (n = 69), the intrinsic rate of natural increase (r_md^-1), calculated according to the Lotka equation, was 1.375, the net reproductive rate (R₀) 291, the mean generation time (T) 90 h, and the minimum generation time (T_min) 73.0 h. The corresponding values for strain MY6 (n = 72) were r_m = 1.460, R₀ = 289, T = 84 h, and T_min = 67.3 h. Peak egg-laying rates in both strains exceeded 140 eggs d^-1. Juvenile and early adulthood mortality was negligible. Strain N2 lived, on average, for 16.7 d, while strain MY6 died 2 days earlier; however, differences in survivorship curves were statistically non-significant.

Conclusion

We found no evidence that adaptation to the laboratory altered the life history traits of C. elegans strain N2. Our results, discussed in the light of earlier studies on C. elegans, demonstrate certain advantages of the hanging drop method in investigations of nematode life cycles. Assuming that its reproducibility is validated in further studies, the method will reduce the inter-laboratory variability of life-history estimates and may ultimately prove to be more convenient than the current standard methods used by C. elegans researchers.

The cellular geometry of growth drives the amino acid economy of Caenorhabditis elegans

The nematode Caenorhabditis elegans grows largely by increases in cell size. As a consequence of this, the surface: volume ratio of its cells must decline in the course of postembryonic growth. Here we use transcriptomic and metabolomic data to show that this change in geometry can explain a variety of phenomena during growth, including: (i) changes in the relative expression levels of cytoplasmic and membrane proteins; (ii) changes in the relative usage of the twenty amino acids in expressed proteins, as estimated by changes in the transcriptome; and (iii) changes in metabolite pools of free amino acids. We expect these relations to be universal in single cells and in whole multicellular organisms that grow largely by increases in cell size, but not those that grow by cell proliferation.

cGMP-dependent protein kinase: linking foraging to energy homeostasis

Successful foraging is necessary for procurement of nutritional resources essential for an animal’s survival. Maintenance of foraging and food acquisition is dependent on the ability to balance food intake and energy expenditure. This review examines the role of cGMP-dependent protein kinase (PKG) as a regulator of foraging behaviour, food acquisition, and energy balance. The role of PKG in food-related behaviours is highly conserved among worms, flies, bees, ants, and mammals. A growing body of literature suggests that PKG plays an integral role in the component behaviours and physiologies underlying foraging behaviour. These include energy acquisition, nutrient absorption, nutrient allocation, nutrient storage, and energy use. New evidence suggests that PKG mediates both neural and physiological mechanisms underlying these processes. This review illustrates how investigating the role of PKG in energy homeostasis in a diversity of organisms can offer a broad perspective on the mechanisms mediating energy balance.

C. elegans dauer formation and the molecular basis of plasticity

Because life is often unpredictable, dynamic, and complex, all animals have evolved remarkable abilities to cope with changes in their external environment and internal physiology. This regulatory plasticity leads to shifts in behavior and metabolism, as well as to changes in development, growth, and reproduction, which is thought to improve the chances of survival and reproductive success. In favorable environments, the nematode Caenorhabditis elegans develops rapidly to reproductive maturity, but in adverse environments, animals arrest at the dauer diapause, a long-lived stress resistant stage. A molecular and genetic analysis of dauer formation has revealed key insights into how sensory and dietary cues are coupled to conserved endocrine pathways, including insulin/IGF, TGF-beta, serotonergic, and steroid hormone signal transduction, which govern the choice between reproduction and survival. These and other pathways reveal a molecular basis for metazoan plasticity in response to extrinsic and intrinsic signals.