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Nat Prod Rep,
2017]
The nematode Caenorhabditis elegans produces tens, if not hundreds, of different ascarosides as pheromones to communicate with other members of its species. Overlapping mixtures of these pheromones affect the development of the worm and a variety of different behaviors. The ascarosides represent a unique tool for dissecting the neural circuitry that controls behavior and that connects to important signaling pathways, such as the insulin and TGF pathways, that lie at the nexus of development, metabolism, and lifespan in C. elegans. However, the exact physiological roles of many of the ascarosides are unclear, especially since many of these pheromones likely have multiple functions depending on their concentrations, the presence of other pheromones, and a variety of other factors. Determining these physiological roles will be facilitated by top-down approaches to characterize the pheromone receptors and their function, as well as bottom-up approaches to characterize the pheromone biosynthetic enzymes and their regulation.
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[
Nat Chem Biol,
2017]
The existence of small-molecule signals that influence development in Caenorhabditis elegans has been known for several decades, but only in recent years have the chemical structures of several of these signals been established. The identification of these signals has enabled connections to be made between these small molecules and fundamental signaling pathways in C. elegans that influence not only development but also metabolism, fertility, and lifespan. Spurred by these important discoveries and aided by recent advances in comparative metabolomics and NMR spectroscopy, the field of nematode chemistry has the potential to expand dramatically in the coming years. This Perspective will focus on small-molecule pheromones and hormones that influence developmental events in the nematode life cycle (ascarosides, dafachronic acids, and nemamides), will cover more recent work regarding the biosynthesis of these signals, and will explore how the discovery of these signals is transforming our understanding of nematode development and physiology.
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Proc Natl Acad Sci U S A,
2009]
To sense its population density and to trigger entry into the stress-resistant dauer larval stage, Caenorhabditis elegans uses the dauer pheromone, which consists of ascaroside derivatives with short, fatty acid-like side chains. Although the dauer pheromone has been studied for 25 years, its biosynthesis is completely uncharacterized. The
daf-22 mutant is the only known mutant defective in dauer pheromone production. Here, we show that
daf-22 encodes a homolog of human sterol carrier protein SCPx, which catalyzes the final step in peroxisomal fatty acid beta-oxidation. We also show that
dhs-28, which encodes a homolog of the human d-bifunctional protein that acts just upstream of SCPx, is also required for pheromone production. Long-term
daf-22 and
dhs-28 cultures develop dauer-inducing activity by accumulating less active, long-chain fatty acid ascaroside derivatives. Thus,
daf-22 and
dhs-28 are required for the biosynthesis of the short-chain fatty acid-derived side chains of the dauer pheromone and link dauer pheromone production to metabolic state.
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[
Nat Chem Biol,
2007]
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.
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Curr Opin Chem Biol,
2019]
The search for novel pheromones, hormones, and other types of natural products in the nematode Caenorhabditis elegans has accelerated over the last 10-15 years. Many of these natural products perturb fundamental processes such as developmental progression, metabolism, reproductive and somatic aging, and various behaviors and have thus become essential tools for probing these processes, which are difficult to study in higher organisms. Furthermore, given the similarity between C. elegans and parasitic nematodes, these natural products could potentially be used to manipulate the development and behavior of parasitic nematodes and target the infections caused by them.
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[
Org Lett,
2009]
In Caenorhabditis elegans, the dauer pheromone, which consists of a number of derivatives of the 3,6-dideoxysugar ascarylose, is the primary cue for entry into the stress-resistant, "nonaging" dauer larval stage. Here, using activity-guided fractionation and NMR-based structure elucidation, a structurally novel, indole-3-carboxyl-modified ascaroside is identified that promotes dauer formation at low nanomolar concentrations but inhibits dauer formation at higher concentrations.
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[
Proc Natl Acad Sci U S A,
2008]
In the model organism Caenorhabditis elegans, the dauer pheromone is the primary cue for entry into the developmentally arrested, dauer larval stage. The dauer is specialized for survival under harsh environmental conditions and is considered "nonaging" because larvae that exit dauer have a normal life span. C. elegans constitutively secretes the dauer pheromone into its environment, enabling it to sense its population density. Several components of the dauer pheromone have been identified as derivatives of the dideoxy sugar ascarylose, but additional unidentified components of the dauer pheromone contribute to its activity. Here, we show that an ascaroside with a 3-hydroxypropionate side chain is a highly potent component of the dauer pheromone that acts synergistically with previously identified components. Furthermore, we show that the active dauer pheromone components that are produced by C. elegans vary depending on cultivation conditions. Identifying the active components of the dauer pheromone, the conditions under which they are produced, and their mechanisms of action will greatly extend our understanding of how chemosensory cues from the environment can influence such fundamental processes as development, metabolism, and aging in nematodes and in higher organisms.
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International Worm Meeting,
2017]
Many animal species change their behavior according to their stage of development. Although such behavioral changes are thought to be important for their fitness, neural modifications that underlie the changes are not fully understood. Caenorhabditis elegans changes their olfactory preferences during development. Larvae exhibit a weak chemotactic response to a food-associated odor diacetyl, whereas adults exhibit a strong response. Previously, we showed that germline proliferation is required for the olfactory changes. The adult worms lacking germline cells failed to exhibit a strong response to diacetyl. In addition to that, we recently found that pheromone sensation is also required for the regulation. The adult worms which have defects either in pheromone synthesis or in a pair of pheromone-sensing neurons, ASK, failed to exhibit strong chemotactic response to diacetyl at adult regardless of whether their germline cells proliferates normally. Here, we have tested the possibility that germline proliferation might principally affect pheromone sensitivity, and the enhanced perception of pheromones subsequently cause the enhanced chemotaxis to diacetyl. By utilizing a Ca2+ indicator, YC3.60, we observed the neuronal responses of ASK sensory neurons to pheromone stimuli consisting of ascaroside C3, C6, C9. Contrary to our expectations, the responses to pheromones of adult worms lacking germline cells were indistinguishable from those of the adult animals with an intact germline. Thus, it seems that germline proliferation and pheromone sensation may act in parallel to regulate chemotaxis. Now we are planning to observe the neuronal activities in the olfactory circuit of pheromone-synthesis defective animals under diacetyl stimuli. Further analyses will reveal how the animals change their behavior by integrating their internal states and environmental inputs.
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[
International Worm Meeting,
2009]
In the nematode Caenorhabditis elegans the endogenously produced ascarosides differentially regulate development and behaviour. At low concentrations, ascarosides act as mating signal (Srinivasan, 2008), whereas at higher concentrations, they induce developmental arrest at the dauer stage (Butcher, 2007, Butcher 2008). Here we report that the ascarosides ascr#2 and ascr#3 influence adult lifespan and stress tolerance of C. elegans. Combinations of ascr#2 and ascr#3 increased lifespan of wild type animals by 30 % and increased thermotolerance up to 70%. Thermotolerance and ageing assays in different mutant background revealed complex regulatory networks for the activity of ascr#2 and 3. Notably, only ascr#3-, but not ascr#2-, mediated heat stress and tolerance and longevity are abolished in reduced insulin signalling background indicating that ascr#2 and ascr#3 act through different pathways. Ascr#2 and ascr#3-mediated increases in ageing and thermotolerance are dependent on the histone deacetylases SIR2.1 and SIR2.3, which also mediate caloric restriction-dependent increases in lifespan. These studies provide the first examples for endogenous small molecules that strongly increase lifespan and thermotolerance.
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Dar, A.R., Basso, K.B., Feng, L., Gordon, M.T., Liu, Y., Butcher, R.A.
[
International Worm Meeting,
2019]
The nemamides are the only assembly-line polyketide-nonribosomal peptides known to be produced by an animal system. These natural products are biosynthesized by two megaenzymes, PKS-1 and NRPS-1, in the canal-associated (CAN) neurons and promote survival during starvation-induced larval arrest in C. elegans. Here, we use CRISPR-Cas9 to sequentially inactivate enzymatic domains in PKS-1 and NRPS-1 in order to trap biosynthetic intermediates and map the assembly-line process that leads to the nemamides. We identify seven additional enzymes, including a methyltransferase and a CoA ligase, that function in trans in nemamide biosynthesis. We show that a surprisingly high percentage of genes that are expressed in the CAN neurons are devoted to nemamide production. By analyzing the biosynthetic intermediates that accumulate in mutant strains lacking these enzymes, we show how these enzymes integrate into the assembly-line process of nemamide biosynthesis. Furthermore, we verify the enzymatic role of these enzymes using in vitro activity assays. Our work reveals a number of noncanonical features to nemamide biosynthesis and provides new insights into the trafficking and role of polyketide-nonribosomal peptides the context of an animal system.