-
[
Stadler Genetics Symposium,
1977]
C. elegans is a roundworm, a free-living soil nematode. The dauer larva is a non-feeding, non-growing larval stage which is formed under conditions of starvation. It possesses a relatively impermeable cuticle and differs from all other larval stages in behavior and morphology. Dauer larva formation is a "developmental switch" in the life cycle which offers special advantages for genetic study. A partial genetic pathway for dauer larva formation has been established. Genetic characterization of additional mutants should reveal more details of this pathway. One class of mutants already characterized exhibits morphological alterations in sensory neurons, as determined by electron microscopy. Such mutants are useful for the study of nerve morphogenesis.
-
[
Curr Biol,
2005]
Despite low global diversity among natural populations of Caenorhabditis elegans, neighboring populations can be as genetically distinct as strains from different continents, probably owing to transient bottlenecks and ongoing dispersal as a dauer larva. Selfing predominates in the wild, but rare outcrossing may also play an important role.
-
[
IUBMB Life,
2009]
Dauer is a dormancy state that may occur at the end of developmental stage L1 or L2 of Caenorhabditis elegans when the environmental conditions are unfavorable (e.g., lack of food, high temperature, or overcrowding) for further growth. Dauer is a nonaging duration that does not affect the postdauer adult lifespan. Major molecular events would include the sensing of the environmental cues, the transduction of the signals into the cells, and the subsequent integration of the signals that result in the corresponding alteration of the metabolism and morphology of the organism. Genetics approach has been effectively used in identifying many of the so-called daf genes involved in dauer formation using C. elegans as the model. Nevertheless, biochemical studies at the protein and metabolic level has been lacking behind in understanding this important life phenomenon. This review focuses on the biochemical understanding so far achieved on dauer formation and dormancy in general, as well as important issues that need to be addressed in the future.
-
[
Autophagy,
2007]
Autophagy is a catabolic process in which long-lived proteins and organelles are degraded for recycling in the cytoplasm. In the nematode Caenorhabditis elegans autophagy is associated with formation of the dauer larva, an alternative developmental stage that worms can enter under poor growth conditions. We have shown that C. elegans mutants that experience caloric restriction because they are feeding-defective also exhibit elevated autophagy and decreased levels of fat deposits, as well as smaller cells and, consequently, a smaller body size. Our results suggest novel relationships between caloric restriction, longevity, body size and autophagy.
-
[
WormBook,
2013]
Cell isolation and culture are essential tools for the study of cell function. Isolated cells grown under controlled conditions can be manipulated and imaged at a level of resolution that is not possible in whole animals or even tissue explants. Recent advances have allowed for large-scale isolation and culture of primary C. elegans cells from both embryos and all four larval stages. Isolated cells can be used for single-cell profiling, electrophysiology, and high-resolution microscopy to assay cell autonomous development and behavior. This chapter describes protocols for the isolation and culture of C. elegans embryonic and larval stage cells. Our protocols describe isolation of embryonic and L1 stage cells from nematodes grown on high-density NA22 bacterial plates and isolation of L2 through L4 stage cells from nematodes grown in axenic liquid culture. Both embryonic and larval cells can be isolated from nematode populations within 3 hours and can be cultured for several days. A primer on sterile cell culture techniques is given in the appendices.
-
[
Bioessays,
1993]
The dauer larva is a specialized third-larval stage of Caenorhabditis elegans that is long-lived and resistant to environmental insult. The dauer larva is formed in response to a high external concentration of a constitutively secreted pheromone. Response to the dauer-inducing pheromone of C. elegans is a promising genetic model for metazoan chemosensory transduction. More than 20 genes have been identified that are required for normal pheromone response. The functions of these genes include production of the pheromone, exposure of sensory neuron endings to the environment, structural and functional integrity of those sensory endings, and the capacity of sensory neurons to make appropriate output. Genetic evidence suggests that two partially redundant sensory pathways act in concert to control dauer formation. At least two classes of chemosensory neurons, ADF and ASI, are implicated in the pheromone response. On the basis of on these findings, a speculative model for the pheromone response is proposed. In this model, the neurons ADF and ASI are pheromone sensors that repress dauer formation in the absence of pheromone and derepress dauer formation in response to pheromone. It is currently unclear whether or not the two genetically defined sensory pathways both act in ADF and ASI.
-
[
Curr Top Dev Biol,
2008]
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.
-
[
Vet Parasitol,
1999]
Nematode parasites of warm-blooded hosts use chemical and thermal signals in host-finding and in the subsequent resumption of development. The free-living nematode Caenorhabditis elegans is a useful model for investigating the chemo- and thermosensory neurons of such parasites, because the functions of its amphidial neurons are well known from laser microbeam ablation studies. The neurons found in the amphidial channel detect aqueous chemoattractants and repellants; the wing cells-flattened amphidial neurons-detect volatile odorants. The finger cells-digitiform amphidial neurons-are the primary thermoreceptors. Two neuron classes, named ADF and ASI, control entry into the environmentally resistant resting and dispersal dauer larval stage, while the paired ASJ neurons control exit from this stage. Skin-penetrating nematode parasites, i.e. the dog hookworm Ancylostoma caninum, and the threadworm, Strongyloides stercoralis, use thermal and chemical signals for host-finding, while the passively ingested sheep stomach worm, Haemonchus contortus, uses environmental signals to position itself for ingestion. Amphidial neurons presumably recognize these signals. In all species, resumption of development, on entering a host, is probably triggered by host signals also perceived by amphidial neurons. In the amphids of the A. caninum infective larva, there are wing- and finger-cell neurons, as well as neurons ending in cilia-like dendritic processes, some of which presumably recognize a sequence of signals that stimulate these larvae to attach to suitable hosts. The functions of these neurons can be postulated, based on the known functions of their homologs in C. elegans. The threadworm, S. stercoralis, has a complex life cycle. After leaving the host, soil-dwelling larvae may develop either to infective larvae (the life-stage equivalent of dauer larvae) or to free-living adults. As with the dauer larva of C. elegans, two neuron classes control this developmental switch. Amphidial neurons control chemotaxis to a skin extract, and a highly modified amphidial neuron, the lamellar cell, appears to be the primary thermoreceptor, in addition to having chemosensory function. The stomach worm, Haemonchus contortus, depends on ingestion by a grazing host. Once ingested, the infective larva is exposed to profound environmental changes in the rumen. These changes stimulate resumption of development in this species. We hypothesize that resumption of development is under the control of the ASJ neuronal pair. Identification of the neurons that control the infective process could provide the basis for entirely new approaches to parasite control involving interference with development at the time and place of initial host-contact.
-
[
Int J Parasitol,
2002]
The signal transduction pathways involved in regulating developmental arrest in the free-living nematode, Caenorhabditis elegans, are fairly well characterised. However, much less is known about how these processes may influence the developmental timing and maturation in helminth parasites. Here, we provide an overview of two signalling pathways implicated in the regulation of dauer larva formation in C. elegans, the insulin-like signalling pathway and the transforming growth factor-beta pathway, and explore what is known about these signalling pathways in a variety of parasitic helminths. Understanding the differences about how these pathways are affected by environmental cues in free-living versus parasitic species of helminths may provide insights into novel mechanisms for the control or prevention of helminth-induced disease.
-
[
Planta,
2015]
MAIN CONCLUSION: The hypometabolic, stress-resistant dauer larva of Caenorhabditis elegans serves as an excellent model to study the molecular mechanisms of desiccation tolerance, such as maintenance of membrane organization, protein folding, xenobiotic and ROS detoxification in the dry state. Many organisms from diverse taxa of life have the remarkable ability to survive extreme desiccation in the nature by entering an ametabolic state known as anhydrobiosis (life without water). The hallmark of the anhydrobiotic state is the achievement and maintenance of an exceedingly low metabolic rate, as well as preservation of the structural integrity of the cell. Although described more than three centuries ago, the biochemical and biophysical mechanisms underlying this phenomenon are still not fully comprehended. This is mainly due to the fact that anhydrobiosis in animals was studied using non-model organisms, which are very difficult, if not impossible, to manipulate at the molecular level. Recently, we introduced the roundworm (nematode) Caenorhabditis elegans as a model for anhydrobiosis. Taking advantage of powerful genetic, biochemical and biophysical tools, we investigated several aspects of anhydrobiosis in a particular developmental stage (the dauer larva) of this organism. First, our studies allowed confirming the previously suggested role of the disaccharide trehalose in the preservation of lipid membranes. Moreover, in addition to known pathways such as reactive oxygen species defense, heat-shock and intrinsically disordered protein expression, evidence for some novel strategies of anhydrobiosis has been obtained. These are increased glyoxalase activity, polyamine and polyunsaturated fatty acid biosynthesis. All these pathways may constitute a generic toolbox of anhydrobiosis, which is possibly conserved between animals and plants.