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[
1987]
We describe the use of a nonspecific carboxylesterase as a biochemical marker for intestinal differentiation in the nematode C. elegans. In particular, we describe how esterase expression responds to inhibition of embryonic DNA synthesis by aphidicolin. Esterase expression requires a short period of DNA synthesis immediattely after the gut lineage is clonally established. However, the subsequent 2-3 rounds of DNA synthesis, which normally occur before esterase gene transcription, can be inhibited without effect. Thus esterase expression depends neither on reaching the normal DNA:cytoplasmic ration nor on counting the normal number of replication rounds.
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[
1990]
The biological processes collectively called aging are being dissected in our laboratory using classic genetic analyses akin to those used in the dissection of other fundamental biological processes, e.g., development or metabolism. Many pitfalls are inherent in the genetic analysis of components of fitness; many result from effects of inbreeding. These inbreeding effects have been avoided by the use of the small free-living nematode Caenorhabditis elegans. The hermaphroditic life-style of this animal facilitates the analysis of life span and senescence by permitting the direct isolation and genetic analysis of long-lived mutants and recombinant inbred (RI) lines without complications resulting from inbreeding problems. Both approaches to obtaining long-lived genotypes have been used effectively in the analysis of the aging processes of C. elegans and the reader will find a brief summary of
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[
1998]
The use of antibodies to visualize the distribution and subcellular localization of gene products powerfully complements genetic and molecular analysis of gene function in C. elegans. The challenge to immunolabeling C. elegans is finding the fixation and permeabilization methods that effectively make antigens accessible without destroying the tissue morphology or the antigen. Embryos are surrounded by a chitinous eggshell and larvae and adults are surrounded by a collagenous cuticle, each of which must be permeabilized to allow penetration of antibodies. In addition, antigens and antibodies are sensitive to different fixing and permeabilizing conditions. For example, some antibodies do not work well on paraformaldehyde-fixed samples, and others are sensitive to incubation in acetone. There are many protocols used in the C. elegans field; additional protocols are summarized in Miller and Shakes (1994) and on the C. elegans World
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[
1997]
Caenorhabditis elegans aquatic toxicity assays were standardized with five common reference toxicants: CdCl2, NaCl, KCl, sodium lauryl sulfate (SLS), and sodium pentachlorophenate (PCP). Aquatic toxicity testing was conducted in 3 media: a standard C. elegans medium; EPA moderately hard reconstituted water; and EPA moderately hard mineral water. Test duration in each medium was 24h without a food source, and 24h and 48h with Escherichia coli strain OP50 as a food source. Each test was replicated three times with each replicate having 6 wells per concentration, 10 worms per well. LC50 values were calculated using probit analysis. The average LC50s for each set of replicants were compared to assess sensitivity and reproducibility of the data, identifying expected variation between replicate tests. These reference toxicants increase the database for C. elegans and provide a benchmark for further application.
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[
1998]
The use of antibodies to visualize the distribution and subcellular localization of gene products powerfully complements genetic and molecular analysis of gene function in C. elegans. The challenge to immunolabeling C. elegans is finding the fixation and permeabilization methods that effectively make antigens accessible without destroying the tissue morphology or the antigen. Embryos are surrounded by a chitinous eggshell and larvae and adults are surrounded by a collagenous cuticle, each of which must be permeabilized to allow penetration of antibodies. In addition, antigens and antibodies are sensitive to different fixing and permeabilizing conditions. For example, some antibodies do not work well on paraformaldehydefixed samples, and others are sensitive to incubation in acetone. There are many protocols used in the C. elegans field; additional protocols are summarized in Miller and Shakes (1994) and on the C. elegans World Wide Web page
(http://elegans.swmed.edu/). -
[
1998]
In this study initial data were generated to develop laboratory control charts for aquatic toxicity testing using the nematode Caenorhabditis elegans. Tests were performed using two reference toxicants: CdCl2 and CuCl2. All tests were performed for 24 h without a food source and for 48 h with a food source in a commonly used nematode aquatic medium. Each test was replicated 6 times with each replicate having 6 wells per concentration with 10 +/- 1 worms per well. Probit analysis was used to estimate LC50 values for each test. The data were used to construct a mean laboratory control chart for each reference toxicant. The coefficient of variation (CV) for three of the four reference toxicant tests was less than 20%, which demonstrates an excellent degree of reproducibility. These CV values are well within suggested standards for determination of organism sensitivity and overall test system credibility. A standardized procedure for performing 24 h and 48 h aquatic toxicity studies with C. elegans is
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[
2012]
Genetic divergence appears to be high among nematodes, while morphological variation is low. To better understand how this fits together and to trace the evolution of development in this phylum we started a comprehensive comparative survey of embryogenesis comprising all branches of the phylogenetic tree. We find considerable differences, in particular between basal and more derived species. This review focuses on cellular pattern formation and cell fate assignment during early development. Our data indicate that evolution of nematodes went from indeterminate early cleavage without initial polarity to invariant cell lineages with establishment of polarity before first division. Different ways to establish this polarity and the variety of taxon-specific spatial arrangements of cells require modifications with respect to cell specification processes and the underlying molecular mechanisms. We conclude that the standard pattern as found in the model system C. elegans constitutes only one of the many ways to construct a nematode and discuss the adaptive value of the observed developmental variations.
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[
WormBook,
2005]
A wide variety of bacterial pathogens, as well as several fungi, kill C. elegans or produce non-lethal disease symptoms. This allows the nematode to be used as a simple, tractable model host for infectious disease. Human pathogens that affect C. elegans include Gram-negative bacteria of genera Burkholderia, Pseudomonas, Salmonella, Serratia and Yersinia; Gram-positive bacteria Enterococcus, Staphylococcus and Streptococcus; and the fungus Cryptococcus neoformans. Microbes that are not pathogenic to mammals, such as the insect pathogen Bacillus thuringiensis and the nematode-specific Microbacterium nematophilum, are also studied with C. elegans. Many of the pathogens investigated colonize the C. elegans intestine, and pathology is usually quantified as decreased lifespan of the nematode. A few microbes adhere to the nematode cuticle, while others produce toxins that kill C. elegans without a requirement for whole, live pathogen cells to contact the worm. The rapid growth and short generation time of C. elegans permit extensive screens for mutant pathogens with diminished killing, and some of the factors identified in these screens have been shown to play roles in mammalian infections. Genetic screens for toxin-resistant C. elegans mutants have identified host pathways exploited by bacterial toxins.
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[
WormBook,
2005]
Ion channels are the "transistors" (electronic switches) of the brain that generate and propagate electrical signals in the aqueous environment of the brain and nervous system. Potassium channels are particularly important because, not only do they shape dynamic electrical signaling, they also set the resting potentials of almost all animal cells. Without them, animal life as we know it would not exist, much less higher brain function. Until the completion of the C. elegans genome sequencing project the size and diversity of the potassium channel extended gene family was not fully appreciated. Sequence data eventually revealed a total of approximately 70 genes encoding potassium channels out of the more than 19,000 genes in the genome. This seemed to be an unexpectedly high number of genes encoding potassium channels for an animal with a small nervous system of only 302 neurons. However, it became clear that potassium channels are expressed in all cell types, not only neurons, and that many cells express a complex palette of multiple potassium channels. All types of potassium channels found in C. elegans are conserved in mammals. Clearly, C. elegans is "simple" only in having a limited number of cells dedicated to each organ system; it is certainly not simple with respect to its biochemistry and cell physiology.
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[
1996]
In recent years it has come to be appreciated that cells do not die only as a consequence of injury or disease-they can also be genetically directed to undergo death during the normal course of development and homeostasis. Disease states can result if cell death is inappropriately timed, as observed in degenerative disorders, or if cells do not die when they should, as in the case of various malignancies and cancers. Without question, an understanding of the mechanisms of cell death is of key significance to human health. Studies of cell death in both invertebrate and vertebrate systems have revealed that the genetic instructions for the regulation and execution of normal programmed cell death, also referred to as apoptotic death, have been remarkably conserved. Analyses in the simple nematode Caenorhabditis elegans have provided significant insight into the mechanism of programmed cell death. Less is clear about the mechanisms of inappropriate or pathological cell death, but a detailed molecular model of one inherited neurodegenerative condition identified in the nematode is being elaborated that may provide a means of identifying the genetic requirements for pathological cell death. Here we review molecular and genetic characterization of programmed and pathological cell death in C. elegans and consider how similar mechanisms of cell death may influence health and aging of higher organisms.