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[
2017]
An organism's health depends on the integrity of molecular and biochemical networks responsible for ensuring homeostasis within its cells and tissues. However, upon aging, a progressive failure in the maintenance of this homeostatic balance occurs in response to various insults, allowing the accumulation of damage, the physiological decline of individual tissues, and susceptibility to diseases. Despite the complex nature of the aging process, simple genetic and environmental alterations can cause an increase in healthy lifespan or "healthspan" in laboratory model organisms. Genetic manipulations of model organisms including yeast, worms, flies, and mice have revealed signaling elements involved in DNA damage, stem cells maintenance, proteostasis, energy, and oxidative metabolism (Riera et al., 2016). However, one of the most intriguing discoveries made in these models resides in the ability of environmental factors to profoundly alter the aging process by remodeling some of the genetic programs mentioned above (Riera and Dillin, 2016). The first line of evidence that an external cue could powerfully regulate longevity was obtained by performing dietary restriction in rodents, a reduction in food intake without malnutrition. Dietary restriction is the most robust intervention to increase lifespan in model organisms including rodents and primates, and delays the emergence of age-related diseases (Mair and Dillin, 2008). How dietary restriction extends lifespan remains an open question, but decades of research are evidencing molecular pathways embedded in the response to reduce energy availability, resulting in the emergence of an altered metabolic state that promotes health and longevity. Nonetheless, the discovery of dietary restriction opened a new avenue of research in the aging field, and in particular in the understanding of how animals deal with fluctuating energy levels in their natural environment, and how their longevity is affected by such factors. This is particularly relevant for the nematode Caenorhabditis elegans, which survives in a changing environment and must be able to coordinate energy-demanding processes including basal cellular functions, growth, reproduction, and physical activity with available external resources. In order to sense their environment, C. elegans possess ciliated sensory neurons located primarily in sensory organs in the head and tail regions. Cilia function as sensory receptors, expressing many G protein-coupled receptors (GPCRs) and transient receptor potential (TRP) channels, and mutants with defective sensory cilia have impaired sensory perception (Bargmann, 2006). Cilia are membrane-bound microtubule-based structures and in C. elegans are only found at the dendritic endings of sensory neurons. Sensory neurons provide nematodes with a remarkable form of developmental plasticity, allowing them to assess food availability, temperature, and crowding information (worm density) in order to arrest their development if required, thus forming long-lived and stress-resistant dauer larvae (Bargmann, 2006; Golden and Riddle, 1982). When favorable times return, worms assess the same cues to recover and resume normal development. As the entry and exit of the dauer larval stage suggest, worm sensory neurons truly function as neuroendocrine organs, being implicated in many physiological functions in addition to their behavioral role (Bargmann, 2006). Much information on these neurons has been gathered from laser ablation experiments and analysis of mutants presenting defects in sensory cilia. A seminal discovery in the aging field was achieved when the laboratory of Cynthia Kenyon showed in 1999 that mutations that cause various defects in cilia formation, including the absence of cilia, deletion of middle and distal segments, or impair chemosensory signal transduction increase longevity profoundly (Apfeld and Kenyon, 1999). Later, this group also demonstrated that laser ablation of specific pairs of gustatory and olfactory chemosensory neurons was sufficient to extend lifespan (Alcedo and Kenyon, 2004). What is the role of TRP channels in modulating these neuroendocrine processes, and what kind of stimuli are these receptors detecting to control aging? This chapter summarizes relevant discoveries that clarify some of the roles of TRP channels in the aging process.
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[
1960]
For the purpose of the present chapter the noun 'cultivation' is to be taken as the maintenance, in the laboratory, of a population of organisms belonging to a desired species through successive generations and subcultures over a prolonged period of time (weeks, months, or years). This is a deliberate restriction of the term. The noun 'culture' is most aptly used for a population within a circumscribed vessel or container (test-tube, Petri dish, U.S. Bureau of Plant Industry watch glass, etc.); it is also used in a looser, more general way (as "in culture") to cover conditions of substantial growth whether or not leading to cultivation in the strict sense
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[
Methods Cell Biol,
1995]
Geneticists like to point out that the ultimate test of a proposed function for a gene and its encoded product (or products) in a living organism involves making a mutant and analyzing its phenotype. This is the goal of reverse genetics: a gene is cloned and sequenced, its transcripts and protein coding sequence are analyzed, and a function may be proposed; one must then introduce a mutation in the gene in a living organism to see what the functional consequences are. The analysis of genetic mosaics takes this philosophy a step further. In mosaics, some cells of an individual are genotypically mutant and other cells are genotypically wild type. One then asks what the phenotypic consequences are for the living organism. This is not the same as asking what cells transcribe the gene or in what cells the protein product of the gene is to be found, but rather it is asking in what cells the wild-type gene is needed for a given function...
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[
1990]
Induction of the C. elegans vulva is a simple example of pattern formation in which the combined action of two intercellular signals specifies three cell types in a precise spatial pattern. These two signals, a graded inductive signal and a short-range lateral signal, are each mediated by a distinct genetic pathway. To understand how these intercellular signals specify cell type, we are studying, by genetic analysis and molecular cloning, genes whose products are involved in the induction pathway.
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[
2000]
Computer tracking of Caenorhabditis elegans, a free-living soil nematode, is a promising tool to assess behavioral changes upon exposure to contaminants. A short life cycle, a known genetic make-up, thoroughly studied behavior, and a completely mapped nervous system make C. elegans an attractive soil test organism with many advantages over the commonly used earthworm. Although many toxicity tests have been performed with C. elegans, the majority focused on mortality, a much less sensitive endpoint than behavior. A computer tracking system has been developed to monitor behavioral changes using C. elegans. Because conditions unrelated to specific toxicant exposures, such as changes in temperature, developmental stage, and presence of adequate food sources, can affect behavior, there is a need to standardize tracking procedures. To this end, we have developed reference charts for control movement comparing the movement of four and five day-old adult nematodes. The use of K-medium versus deionized (DI) H2O for pre-tracking rinses was also investigated. A final reference chart compared the behavioral responses of nematodes at various food densities (i.e. bacterial concentrations).
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[
Methods Cell Biol,
1995]
The number of easily distinguishable mutant phenotypes in Caenorhabditis elegans is relatively small, and this constrains the number of factors that can be followed in standard genetic crosses. Consequently, a new mutation is mapped, first to a chromosome using two-factor data from one or more crosses, and then to a chromosomal subregion by successive three-factor crosses. Mapping would be more efficient if it were possible to score a large number of well-distributed markers in a single cross. The advent of the polymerase chain reaction makes this approach feasible by allowing polymorphic genomic regions to serve as genetic markers that are easily scored in DNA released from individual animals. The only "phenotype" is a band on a gel, so the segregation of many of these markers can be followed in a single cross. Following the terminology proposed by Olsen et al. (1989), we refer to polymorphisms that can be scored by appropriately designed polymerase chain reaction (PCR) assays as polymorphic seqeunce-tagged sites (STSs)...
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[
1985]
At first sight the inclusion of a chapter on Caenorhabditis elegans in a volume on cell biology may seem unusual. However this nematode has been a superb model system for a number of cell biology studies as well as a useful model of aging. This widespread interest in C. elegans is engendered in large part by its genetic system and its optical clarity in Nomarski phase-contrast optics. Nematodes have long been a system in wide use among experimental gerontologists, and with the introduction of C. elegans by Brenner in 1974, this species has become the nematode of choice for most aging studies. We concentrate primarily on C. elegans in this review although a number of other speices, including Caenorhabditis briggsae, Turbatrix aceti, and Panagrellus redivivus, have been used in aging studies also. Other reviews on aging in C. elegans have appeared recently, including a more detailed review in another volume of this series.
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[
Lecture Notes in Computer Science,
2008]
One of the most tractable organisms for the study of nervous systems is the nematode Caenorhabditis elegans, whose locomotion in particular has been the subject of a number of models. In this paper we present a first integrated neuro-mechanical model of forward locomotion. We find that a previous neural model is robust to the addition of a body with mechanical properties, and that the integrated model produces oscillations with a more realistic frequency and waveform than the neural model alone. We conclude that the body and environment are likely to be important components of the worms locomotion subsystem.
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[
WormBook,
2005]
Synaptogenesis is a process involving the formation of a neurotransmitter release site in the presynaptic neuron and a receptive field at the postsynaptic partners, and the precise alignment of pre- and post-synaptic specializations. In C. elegans synapses are found as en passant axonal swellings along the nerve processes. Genetic screens using a synaptic vesicle-associated GFP marker have identified key players in synaptic target recognition and organization of the presynaptic terminals. Importantly, the functions of most genes are evolutionarily conserved. Further studies using a combination of genetic modifier screens and reverse genetics have begun to reveal the underlying signaling pathways.
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[
Methods Mol Biol,
2013]
The principle of commonly used methods to create mutations in the nematode Caenorhabditis elegans (C. elegans) is straightforward. In general, worms are exposed to a dose of mutagen resulting in DNA damages and mutations. Screening the progeny of the mutagenized animals for a certain phenotype is the regular forward genetic approach in C. elegans. A mutant selected from such a population is stabilized to recover a pure homozygous strain. In this chapter, we categorize the protocol into mutagenesis, phenotype screen, and outcross and provide time-tested procedures for their implementation to create long-lived worm mutants.