Chemical structure and biological activity of the Caenorhabditis elegans dauer-inducing pheromone

Function of the PHA-4/FOXA transcription factor during C. elegans post-embryonic development

BACKGROUND

pha-4 encodes a forkhead box (FOX) A transcription factor serving as the C. elegans pharynx organ identity factor during embryogenesis. Using Serial Analysis of Gene Expression (SAGE), comparison of gene expression profiles between growing stages animals and long-lived, developmentally diapaused dauer larvae revealed that pha-4 transcription is increased in the dauer stage.

RESULTS

Knocking down pha-4 expression by RNAi during post-embryonic development showed that PHA-4 is essential for dauer recovery, gonad and vulva development. daf-16, which encodes a FOXO transcription factor regulated by insulin/IGF-1 signaling, shows overlapping expression patterns and a loss-of-function post-embryonic phenotype similar to that of pha-4 during dauer recovery. pha-4 RNAi and daf-16 mutations have additive effects on dauer recovery, suggesting these two regulators may function in parallel pathways. Gene expression studies using RT-PCR and GFP reporters showed that pha-4 transcription is elevated under starvation, and a conserved forkhead transcription factor binding site in the second intron of pha-4 is important for the neuronal expression. The vulval transcription of lag-2, which encodes a ligand for the LIN-12/Notch lateral signaling pathway, is inhibited by pha-4 RNAi, indicating that LAG-2 functions downstream of PHA-4 in vulva development.

CONCLUSION

Analysis of PHA-4 during post-embryonic development revealed previously unsuspected functions for this important transcriptional regulator in dauer recovery, and may help explain the network of transcriptional control integrating organogenesis with the decision between growth and developmental arrest at the dauer entry and exit stages.

Quantitative genetic analysis of life-history traits of Caenorhabditis elegans in stressful environments

BACKGROUND

Organisms live in environments that vary. For life-history traits that vary across environments, fitness will be maximised when the phenotype is appropriately matched to the environmental conditions. For the free-living nematode Caenorhabditis elegans, we have investigated how two major life-history traits, (i) the development of environmentally resistant dauer larvae and (ii) reproduction, respond to environmental stress (high population density and low food availability), and how these traits vary between lines and the genetic basis of this variation.

RESULTS

We found that lines of C. elegans vary in their phenotypic plasticity of dauer larva development, i.e. there is variation in the likelihood of developing into a dauer larva for the same environmental change. There was also variation in how lifetime fecundity and the rate of reproduction changed under conditions of environmental stress. These traits were related, such that lines that are highly plastic for dauer larva development also maintain a high population growth rate when stressed. We identified quantitative trait loci (QTL) on two chromosomes that control the dauer larva development and population size phenotypes. The QTLs affecting the dauer larva development and population size phenotypes on chromosome II are closely linked, but are genetically separable. This chromosome II QTL controlling dauer larva development does not encompass any loci previously identified to control dauer larva development. This chromosome II region contains many predicted 7-transmembrane receptors. Such proteins are often involved in information transduction, which is clearly relevant to the control of dauer larva development.

CONCLUSION

C. elegans alters both its larval development and adult reproductive strategy in response to environmental stress. Together the phenotypic and genotypic data suggest that these two major life-history traits are co-ordinated responses to environmental stress and that they are, at least in part, controlled by the same genomic regions.

Chemical Complexity and the Genetics of Aging

We examine how aging is impacted by various chemical challenges that organisms face and by the molecular mechanisms that have evolved to regulate lifespan in response to them. For example, environmental information, which is detected and processed through sensory systems, can modulate lifespan by providing information about the presence and quality of food as well as presence and density of conspecifics and predators. In addition, the diverse forms of molecular damage that result from constant exposure to damaging chemicals that are generated from the environment and from metabolism pose an informatic and energetic challenge for detoxification systems, which are important in ensuring longevity. Finally, systems of innate immunity are vital for recognizing and combating pathogens but are also seen as of increasing importance in causing the aging process. Integrating ideas of molecular mechanism with context derived from evolutionary considerations will lead to exciting new insights into the evolution of aging.

Significance of chirality in pheromone science

Pheromones play important roles in chemical communication among organisms. Various chiral and non-racemic pheromones have been identified since the late 1960s. Their enantioselective syntheses could establish the absolute configuration of the naturally occurring pheromones and clarified the relationships between absolute configuration and bioactivity. For example, neither the (R)- nor (S)-enantiomer of sulcatol, the aggregation pheromone of an ambrosia beetle Gnathotrichus sulcatus, is behaviorally active, while their mixture is bioactive. In the case of olean, the olive fruit fly pheromone, its (R)-isomer is active for the males, and the (S)-isomer is active for the females. About 140 chiral pheromones are reviewed with regard to their stereochemistry-bioactivity relationships. Problems encountered in studying chirality of pheromones were examined and analyzed to think about possible future directions in pheromone science.

Caenorhabditis elegans SDF-9 enhances insulin/insulin-like signaling through interaction with DAF-2

SDF-9 is a modulator of Caenorhabditis elegans insulin/IGF-1 signaling that may interact directly with the DAF-2 receptor. SDF-9 is a tyrosine phosphatase-like protein that, when mutated, enhances many partial loss-of-function mutants in the dauer pathway except for the temperature-sensitive mutant daf-2(m41). We propose that SDF-9 stabilizes the active phosphorylated state of DAF-2 or acts as an adaptor protein to enhance insulin-like signaling.

Genetic analysis of dauer formation in Caenorhabditis briggsae

Molecular changes that underlie evolutionary changes in behavior and physiology are not well understood. Dauer formation in Caenorhabditis elegans is a temperature-sensitive process controlled through a network of signaling pathways associated with sensory neurons and is potentially an excellent system in which to investigate molecular changes in neuronal function during evolution. To begin to investigate the evolution of dauer formation in the genus Caenorhabditis at the molecular level, we isolated dauer-formation mutations in C. briggsae, a species closely related to the model organism C. elegans. We identified mutations in orthologs of C. elegans genes daf-2 (insulin receptor), daf-3 (Smad), and daf-4 (TGF-beta type 2 receptor), as well as genes required for formation of sensory cilia. Phenotypic analyses revealed that functions of these genes are conserved between C. elegans and C. briggsae. Analysis of C. briggsae mutations also revealed a significant difference between the two species in their responses to high temperatures (>26 degrees). C. elegans is strongly induced to form dauers at temperatures above 26 degrees, near the upper limit for growth of C. elegans. In contrast, C. briggsae, which is capable of growth at higher temperatures than C. elegans, lacks this response.

Small-molecule pheromones that control dauer development in Caenorhabditis elegans

In response to high population density or low food supply, the nematode Caenorhabditis elegans enters an alternative larval stage, known as the dauer, that can withstand adverse conditions for prolonged periods. C. elegans senses its population density through a small-molecule signal, traditionally called the dauer pheromone, that it secretes into its surroundings. Here we show that the dauer pheromone consists of several structurally related ascarosides-derivatives of the dideoxysugar ascarylose-and that two of these ascarosides (1 and 2) are roughly two orders of magnitude more potent at inducing dauer formation than a previously reported dauer pheromone component (3) and constitute a physiologically relevant signal. The identification of dauer pheromone components 1 and 2 will facilitate the identification of target receptors and downstream signaling proteins.

Public and private mechanisms of life extension in Caenorhabditis elegans

Model organisms have been widely used to study the ageing phenomenon in order to learn about human ageing. Although the phylogenetic diversity between vertebrates and some of the most commonly used model systems could hardly be greater, several mechanisms of life extension are public (common characteristic in divergent species) and likely share a common ancestry. Dietary restriction, reduced IGF-signaling and, seemingly, reduced ROS-induced damage are the best known mechanisms for extending longevity in a variety of organisms. In this review, we summarize the knowledge of ageing in the nematode Caenorhabditis elegans and compare the mechanisms of life extension with knowledge from other model organisms.

Endocrine disruption in nematodes: effects and mechanisms

This paper reviews the current knowledge on endocrine disruption in nematodes. These organisms have received little attention in the field of ecotoxicology, in spite of their important role in aquatic ecosystems. Research on endocrine regulation and disruption in nematodes, especially the more recent studies, concentrate mainly on one species, Caenorhabditis elegans. Although an endocrine system is not known in nematodes, there is evidence that many processes are regulated via hormonal pathways. As vertebrate hormones, such as steroids, may have endocrine functions in nematodes as well, endocrine disrupting chemicals (EDCs) defined for vertebrates may also be able to influence nematodes. The studies that are reviewed here, and own data showed that potential EDCs can affect nematodes on all organizational levels, from molecules to communities. It is concluded that nematodes, notably its prominent species C. elegans, are a promising organism group for the development of biomonitoring tools, provided that more mechanistic evidence is gathered on hormonal processes within these animals.

Embryo stability and vulnerability in an always changing world

Contrary to the view that embryos and larvae are the most fragile stages of life, development is stable under real-world conditions. Early cleavage embryos are prepared for environmental vagaries by having high levels of cellular defenses already present in the egg before fertilization. Later in development, adaptive responses to the environment either buffer stress or produce alternative developmental phenotypes. These buffers, defenses, and alternative pathways set physiological limits for development under expected conditions; teratology occurs when embryos encounter unexpected environmental changes and when stress exceeds these limits. Of concern is that rapid anthropogenic changes to the environment are beyond the range of these protective mechanisms.

Generation and modulation of chemosensory behaviors in C. elegans

C. elegans recognizes and discriminates among hundreds of chemical cues using a relatively compact chemosensory nervous system. Chemosensory behaviors are also modulated by prior experience and contextual cues. Because of the facile genetics and genomics possible in this organism, C. elegans provides an excellent system in which to explore the generation of chemosensory behaviors from the level of a single gene to the motor output. This review summarizes the current knowledge on the molecular and neuronal substrates of chemosensory behaviors and chemosensory behavioral plasticity in C. elegans.

Mechanisms and evolution of environmental responses in Caenorhabditis elegans

We review mechanistic and evolutionary aspects of interactions between the model organism Caenorhabditis elegans and its environment. In particular, we focus on environmental effects affecting developmental mechanisms. We describe natural and laboratory environments of C. elegans and provide an overview of the different environmental responses of this organism. We then show how two developmental processes respond to changes in the environment. First, we discuss the development of alternative juvenile stages, the dauer and non-dauer larva. This example illustrates how development responds to variation in the environment to generate complex phenotypic variation. Second, we discuss the development of the C. elegans vulva. This example illustrates how development responds to variation in the environment while generating an invariant final phenotype.

C. elegans feeding defective mutants have shorter body lengths and increased autophagy

BACKGROUND

Mutations that cause feeding defects in the nematode C. elegans are known to increase life span. Here we show that feeding defective mutants also have a second general trait in common, namely that they are small.

RESULTS

Our measurements of the body lengths of a variety of feeding defective mutants, or of a variety of double mutants affecting other pathways that regulate body length in C. elegans, i.e. the DBL-1/TGFbeta, TAX-6/calcineurin and the SMA-1/betaH-spectrin pathways, indicate that food uptake acts as a separate pathway regulating body length. In early stages, before eating begins, feeding defective worms have no defect in body length or, in some cases, have only slightly smaller body length compared to wild-type. A significant difference in body length is first noticeable at later larval stages, a difference that probably correlates with increasing starvation. We also show that autophagy is induced and that the quantity of fat is decreased in starved worms.

CONCLUSION

Our results indicate that the long-term starvation seen in feeding-defective C. elegans mutants activates autophagy, and leads to depletion of fat deposits, small cell size and small body size.

Pseudomonad cyclopentadecanone monooxygenase displaying an uncommon spectrum of Baeyer-Villiger oxidations of cyclic ketones

Baeyer-Villiger monooxygenases (BVMOs) are biocatalysts that offer the prospect of high chemo-, regio-, and enantioselectivity in the organic synthesis of lactones or esters from a variety of ketones. In this study, we have cloned, sequenced, and overexpressed in Escherichia coli a new BVMO, cyclopentadecanone monooxygenase (CpdB or CPDMO), originally derived from Pseudomonas sp. strain HI-70. The 601-residue primary structure of CpdB revealed only 29% to 50% sequence identity to those of known BVMOs. A new sequence motif, characterized by a cluster of charged residues, was identified in a subset of BVMO sequences that contain an N-terminal extension of approximately 60 to 147 amino acids. The 64-kDa CPDMO enzyme was purified to apparent homogeneity, providing a specific activity of 3.94 micromol/min/mg protein and a 20% yield. CPDMO is monomeric and NADPH dependent and contains approximately 1 mol flavin adenine dinucleotide per mole of protein. A deletion mutant suggested the importance of the N-terminal 54 amino acids to CPDMO activity. In addition, a Ser261Ala substitution in a Rossmann fold motif resulted in an improved stability and increased affinity of the enzyme towards NADPH compared to the wild-type enzyme (K(m) = 8 microM versus K(m) = 24 microM). Substrate profiling indicated that CPDMO is unusual among known BVMOs in being able to accommodate and oxidize both large and small ring substrates that include C(11) to C(15) ketones, methyl-substituted C(5) and C(6) ketones, and bicyclic ketones, such as decalone and beta-tetralone. CPDMO has the highest affinity (K(m) = 5.8 microM) and the highest catalytic efficiency (k(cat)/K(m) ratio of 7.2 x 10(5) M(-1) s(-1)) toward cyclopentadecanone, hence the Cpd designation. A number of whole-cell biotransformations were carried out, and as a result, CPDMO was found to have an excellent enantioselectivity (E > 200) as well as 99% S-selectivity toward 2-methylcyclohexanone for the production of 7-methyl-2-oxepanone, a potentially valuable chiral building block. Although showing a modest selectivity (E = 5.8), macrolactone formation of 15-hexadecanolide from the kinetic resolution of 2-methylcyclopentadecanone using CPDMO was also demonstrated.

Activation of nicotinic receptors uncouples a developmental timer from the molting timer inC. elegans

C. elegans develops through four larval stages (L1 to L4)separated by molts. The identity of larval stages is mostly determined by stage-specific expression of heterochronic genes, which constitute an intrinsic genetic timer. However, extrinsic cues such as food availability or population density also modulate the developmental timing of C. elegans by mechanisms that remain largely unknown. To investigate a potential role of the nervous system in the temporal regulation of C. elegans development, we pharmacologically manipulated nicotinic neurotransmission, which represents a prominent signaling component in C. elegans nervous system. Exposure to the nicotinic agonist DMPP during post-embryonic development is lethal at the L2/L3 molt. Specifically, it delays cell divisions and differentiation during the L2 stage but does not affect the timing of the molt cycle, hence causing exposure of a defective L3 cuticle to the environment after the L2/L3 molt. Forcing development through a previously uncharacterized L2 diapause resynchronizes these events and suppresses DMPP-induced lethality. Nicotinic acetylcholine receptors (nAChRs)containing the UNC-63 subunit are required, probably in neurons, to trigger the action of DMPP. Using a forward genetic screen, we further demonstrated that the nuclear hormone receptor (NHR) DAF-12 is necessary to implement the developmental effects of DMPP. Therefore, a novel neuroendocrine pathway involving nAChRs and the NHR DAF-12 can control the speed of stage-specific developmental events in C. elegans. Activation of DMPP-sensitive nAChRs during the second larval stage uncouples a molting timer and a developmental timer, thus causing a heterochronic phenotype that is lethal at the subsequent molt.

Small molecule signaling in Caenorhabditis elegans

Whereas the C. elegans genome was sequenced many years ago, the role of small molecule signals in its biology is still poorly understood. A recent publication reports the identification of two steroidal signaling molecules that regulate C. elegans reproductive development and dauer diapause via the nuclear receptor DAF-12. The two compounds, named dafachronic acids, represent the first endogenous ligands identified for any of the 284 nuclear receptors in C. elegans.

Thioredoxin is related to life span regulation and oxidative stress response in Caenorhabditis elegans

Thioredoxin, an oxidoreductase, is a multifunction protein. The thioredoxin system is composed of NADPH, thioredoxin reductase and thioredoxin. This enzyme is highly conserved from bacteria to humans. We have characterized TRX-1, a thioredoxin homolog in C. elegans, which has about 36% identity in amino acid sequence with human thioredoxin. By gfp reporter system, trx-1 has been shown to be restrictedly expressed in ASI and ASJ neurons and in intestine. Immunostaining confirmed the intestinal expression. Full-length cDNA of trx-1 has been isolated by cDNA library PCR and subsequently cloned and sequenced. We have shown that the encoded protein functions as a reductase in the insulin reducing assay. Moreover, we have isolated a deletion mutant by PCR-based TMP-UV mutagenesis method. Mutant animals have reduced life span and are sensitive to oxidative stress. Reintroduction of trx-1 into mutant worms fully restored the wild-type phenotype. Our results suggest that trx-1 has important functions in life span regulation and oxidative stress response in C. elegans.

Parastrongyloides trichosuri, a nematode parasite of mammals that is uniquely suited to genetic analysis

Commonly studied nematode parasites have not proven amenable to simple genetic analyses and this has significantly reduced the available research options. We introduce here a nematode parasite of mammals, Parastrongyloides trichosuri, which has features uniquely suited for genetic analysis. This parasite has the capacity to undergo multiple reproductive cycles as a free-living worm and thereby amplify the numbers of its infective L3s in faeces. Culture conditions are presented that permit facile laboratory maintenance of this worm for >90 free-living life cycles (to date) without the need for re-entry into a permissive host. Even after long maintenance as a free-living worm, culture conditions can be manipulated to favour development of infective L3 worms, which remain able to successfully infect their marsupial hosts. The switch to infective L3 development is triggered by a secreted factor contained in culture medium conditioned by multiple generations of free-living worm culture. It is simple to perform single pair crosses with P. trichosuri to carry out Mendelian genetics in the laboratory and this has been done multiple times with sibling pairs to generate highly inbred lines. Lines of worms can readily be cryopreserved and recovered. Over 7000 expressed sequence tags have been produced from cDNAs at different life cycle stages and used to identify single nucleotide polymorphisms and microsatellites as genetic markers. Free-living worms live only a few days on average while the patency of parasitic infections can last for several months. Since we show this is not the result of re-infection, we conclude that parasitic worms have a lifespan capacity at least 20-30 times longer than their free-living counterparts. We discuss how it should be possible to exploit these unique features of P. trichosuri as a model for future studies that explore the genetic basis of longevity and parasitism.

Alternate metabolism during the dauer stage of the nematode Caenorhabditis elegans

When environmental conditions are unsuitable to support nematode reproduction, Caenorhabditis elegans arrests development before the onset of sexual maturity and specialised 'dauer' larvae, adapted for dispersal, and extended diapause are formed. Dauer larvae do not feed and their metabolism is dependent on internal food reserves. Adult worms which express defects in the insulin/insulin-like growth factor receptor DAF-2 also display enhanced longevity. Whole genome mRNA expression profiling has demonstrated that C. elegans dauer larvae and daf-2 adults have similar transcription profiles for a cohort of longevity genes. Important components of this enhanced longevity system are the alpha-crystallin family of small heat shock proteins, anti-ROS defence systems, increased activity of cellular detoxification processes and possibly also increased chromatin stability and decreased protein turnover. Anaerobic fermentation pathways are upregulated in dauer larvae, while long-lived daf-2 adults appear to have normal oxidative metabolism. Anabolic pathways are down regulated in dauer larvae (and possibly in daf-2 adults as well), and energy consumption appears to be diverted to enhanced cellular maintenance and detoxification processes in both systems.

The prepared mind of the worm

In C. elegans, dauer pheromone is an indicator of population density and influences pathways that regulate metabolism, development, and aging. In a recent publication in Nature, Paik and coworkers (Jeong at al., 2005) show the purified substance to be a pyran ring conjugated to heptanoic acid, setting the stage for dissecting downstream signaling pathways.