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[
1987]
Each year thousands of new chemicals are developed but the potential societal benefits are often unrealized or delayed due to the lack of toxicological data. In the past, chemicals were introduced into the environment with little or no toxicological testing. This has resulted in many examples where adverse effects to humans were seen only after years of exposure (e.g., asbestos, benzene, vinyl chloride). Because few chemicals are used as pure substances, the toxicity of mixtures is another problem. However, these potential chemical interactions are seldom evaluated. All of the above have increased the need for toxicological testing.
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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]
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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[
WormBook,
2005]
Mutations in many genes can result in a similar phenotype. Finding a number of mutants with the same phenotype tells you little about how many genes you are dealing with, and how mutable those genes are until you can assign those mutations to genetic loci. The genetic assay for gene assignment is called the complementation test. The simplicity and robustness of this test makes it a fundamental genetic tool for gene assignment. However, there are occasional unexpected outcomes from this test that bear explanation. This chapter reviews the complementation test and its various outcomes, highlighting relatively rare but nonetheless interesting exceptions such as intragenic complementation and non-allelic non-complementation.
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[
1999]
Caenorhabditis elegans is a free-living soil nematode that is commonly used as a biological model. Recently, much work has been done using the nematode as a toxicological model as well. Much of the work involving C. elegans has been performed in aquatic media, since it lives in the interstitial water of soil. However, testing in soil would be expected to more accurately reproduce the organism's normal environment and may take into consideration other factors not available in an aquatic test, i.e., toxicant availability effects due to sorption, various chemical interactions, etc. This study used a modification of a previous experimental protocol to determine 24h LC50 values for Cu in a Cecil series soil mixture, and examined the use of CuCl2 as a reference toxicant for soil toxicity testing with C. elegans. Three different methods of determining percent lethality were used, each dependent on how the number of worms missing after the recovery process was used in the lethality calculations. Only tests having >/= 80% worm recovery and >/= 90% control survival were used in determining the LC50S, by Probit analysis. The replicate LC50 values generated a control chart for each method of calculating percent lethality. The coefficient of variation (CV) for each of the three methods was </= 14%. The control charts and the protocol outlined in this study are intended to be used to assess test organism health and to monitor precision of future soil toxicity tests with C.
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[
1983]
The advantages of the free-living nematode Caenrohabditis elegans as a model for pharmacologic, toxicant and anthelmintic testing have become apparent to many companies, and the application of this organism as a primary screen for test compounds or toxic agents has expanded rapidly. It is appropriate to briefly summarize some of this nematode's qualities, to invoke an appreciation of this elegant system. As true of many invertebrate test organisms, C. elegans is small (about 1 mm X 40 u at maturity) and has a short life cycle: reproduction starts on day 3-4, ceases by day 14 and by day 25 it dies. Thus, for aging studies, all the symptoms of senescence are compressed into a short time period. In addition, this nematode has a small, fixed number of cells (about 830 at maturity) and differentiated organ systems: nervous, excretory, muscular, digestive and reproductive. The preceding characteristics are not unique in invertebrate model systems and their enumeration fails to explain the increasing popularity of C. elegans as a test organism. To understand this phenomenon several additional facts must be emphasized. First, the selection of C. elegans for detailed studies on the genetic control and regulation of behavior and developmental processes has fostered a wealth of knowledge on its neuroanatomy, cell lineages, biochemistry and behavior. There is now undoubtedly more accumulated knowledge on C. elegans than on any other multicellular creature. It is also the largest metazoan which can be continuously cultured on a chemically defined medium, and though most studies have proceeded on undefined media or in monoxenic culture (utilizing a bacterium as a food source), this property can be exploited for precise nutritional studies. In regard to aging studies, the question of relevance of aging in the nematode to that in mammals has been answered in respect to some parameters which characterize senescence in humans, and further study will define other features of aging which are common to all metazoa. In practical terms, this means that test which require 24-36 months to rear an aged rat for evaluation of a pharmaceutical, can potentially be accomplished in 21 days using the nematode. The paper emphasizes that the use of the C. elegans system as a primary screen for candidate compounds to intervene in the aging process can save time, effort and money, while
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[
2000]
There is growing interest in the use of bioindicators to assess metal toxicity in soil. The current ASTM Standard Guide for Conducting Laboratory Soil Toxicity Test with the lumbricid earthworm Eisenia fetida (E 1676-97) uses a common earthworm. The nematode Caenorhabditis elegans is a natural soil inhabitant with many characteristics that make an ideal alternate test organism. It has been used to assess metal toxicity in aquatic media, agar plates and in soil. Work is currently underway on the design of a C. elegans procedure for metals in soil. The objective of this study was to determine differences in LC50S between the chloride salt and the nitrate salt forms of cadmium, copper, lead, nickel, and zinc, in three types of soil: Cecil, Tifton, and ASTM artificial soil. Results indicated that the toxicological effect of the metallic salt varies and is dependent on the particular metal. For Cd and Pb the nitrate form is more toxic while Cu and Ni are more toxic in the chloride form. The composition of the soil also effected toxicity, with the metal being the least toxic in ASTM soil and more toxic in the Tifton soil. This strongly correlated with organic matter and clay content of the soil. It is important to determine the effects of carrier salt form and soil composition on metal toxicity, not only in order to standardize the protocol for C. elegans soil toxicity testing, but also in establishing acceptable exposure concentrations in the soil.
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[
1977]
Genetic tests for maternal effects have been performed on 25 temperature-sensitive zygote-defective mutants of the nematode Caenorhabditis elegans. For most of the genes defined by these mutants (22 out of 25), maternal expression is sufficient for zygote survival, even if the gene is not expressed in the zygote. Twelve of these 22 genes must be expressed in the mother for zygote survival (strict maternals). For the remaining ten, expression either in the mother or in the zygote is sufficient for survival. One mutant shows a paternal effect in which wild-type sperm cytoplasm appears to rescue mutant zygotes. Maternal effect tests on mutants that block as late as the second larval stage after hatching indicate that in 3 of 11 mutants maternal contributions still can rescue mutant progeny. Temperature shift experiments on the zygote-defective embryos show that all but one of the strict maternal mutants are temperature sensitive only before gastrulation. One of the mutants that can be rescued by gene expression in the zygote is temperature sensitive prior to gastrulation, suggesting that some zygote genes can function in early embryogenesis.
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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.