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[
WormBook,
2005]
Genetic suppression has provided a very powerful tool for analyzing C. elegans. Suppression experiments are facilitated by the ability to handle very large numbers of individuals and to apply powerful selections. Because the animal grows as a self-fertilizing diploid, both dominant and recessive suppressors can be recovered. Many different kinds of suppression have been reported. These are discussed by category, with examples, together with discussion of how suppressors can be used to interpret the underlying biology, and to enable further experimentation. Suppression phenomena can be divided into intragenic and extragenic classes, depending on whether the suppressor lies in the same gene as the starting mutation, or in a different gene. Intragenic types include same-site replacement, compensatory mutation, alteration in splicing, and reversion of dominant mutations by cis- knockout. Extragenic suppression can occur by a variety of informational mechanisms, such as alterations in splicing, translation or nonsense-mediated decay. In addition, extragenic suppression can occur by bypass, dosage effects, product interaction, or removal of toxic products. Within signaling pathways, suppression can occur by modulating the strength of signal transmission, or by epistatic interactions that can reveal the underlying regulatory hierarchies. In C. elegans biology, the processes of muscle development, vulva formation and sex determination have provided remarkably rich arenas for the investigation and exploitation of suppression.
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[
WormBook,
2005]
The normal karyotype of Caenorhabditis elegans, with its five pairs of autosomes and single pair of X chromosomes, is described. General features of chromosomes and global differences between different chromosomal regions are discussed. Abnormal karyotypes, including duplications, deficiencies, inversions, translocations and chromosome fusions are reviewed. The effects of varying ploidy and of varying gene dosage are summarized. Dosage-sensitive genes seem to be rare in C. elegans, and the organism is able to tolerate substantial levels of aneuploidy. However, autosomal hemizygosity for more than about 3 % of the total genome may be incompatible with viability.
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[
1987]
Since the last review in this series [Johnson, 1985], many papers have appeared dealing directly with the aging process in both Caenorhabditis elegans and Turbatrix aceti. We will review this work and also briefly review other areas of C. elegans research that may impact on the study of aging. C. elegans has become a major biological model; four "News" articles in Science [Lewin, 1984a,b; Marx, 1984a,b] and inclusion as one of three developmental genetics models in a recent text [Wilkins, 1986] indicate its importance. Recent work has verified earlier results and has advanced progress toward new goals, such as routine molecular cloning. The aging studies reviewed here, together with new findings from other areas of C. elegans research, lay the groundwork for rapid advances in our understanding of aging in nematodes. Several areas of research in C. elegans have been reviewed recently: the genetic approach to understanding the cell lineage [Sternberg and Horvitz, 1984] and a brief summary of cell lineage mutants [Hedgecock, 1985]. The specification of neuronal development and neural connectivity has been a continuing theme in C. elegans research and reviews of these areas have also appeared [Chalfie, 1984; White, 1985]. A major genetic advance is the development of reliable, if not routine, mosaic analysis [Herman, 1984; Herman and Kari, 1985], which is useful for the genetic analysis of tissue-limited gene expression. Hodgkin [1985] reviews studies on a series of mutants involved in the specification of sex. These include her mutations that cause XO worms (normally males) to develop as hermaphrodites and tra mutations that change XX hermaphrodites into phenotypic males. The work on the structure and development of nematode muscle has been summarized by Waterston and Francis [1985]. A comprehensive review of aging research, containing useful reference material on potential biomarkers, has appeared [Johnson and Simpson, 1985], as well as a review including
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[
1977]
The soil nematode Caenorhabditis elegans was selected 11 years ago by Sydney Brenner as an experimental organism suitable for the isolation of many behavioral mutants and small enough for anatomical analysis of such mutants with the electron microscope. Two distinct goals motivated the initial studies of this organism: first, the hope that some of the mutants would have simple anatomical alterations that could be directly correlated with their behavioral defects, allowing the assignment of specific functions to specific neurons, and second, the hope that the detailed analysis of the kinds of alterations induced by individual mutations and the classes of cells affected by given mutations would reveal general features of the genetic program that specifies the development of the organism. Over the past 11 years the number of investigators working on C. elegans has increased to about 75 and is still growing. Nearly 3,000 different mutants have been isolated and different investigators are pursuing their effects on different cells. My own research is in the development of the nervous system. In particular, I would like to learn something about the workings of the complex black box that connects individual genes to the determination of the morphology of developing neurons. Are there gene products whose specific function is to determine the morphology of cells? If so, what are these gene products and how do they act in the developing cell? One would anticipate that mutations in such hypothetical genes would cause specific morphological alterations in cells. Because the morphology of a neuron determines its function, by selecting behavioral mutants altered in the function of the nervous system one might commonly find mutants that alter the morphology of neurons, and some of these might be in specific morphological genes. It is my hope that it will be possible to compare such mutants to the wild type in order to identify the defective gene products and thereby learn something about the role of normal gene products in determining the development of neurons. In this paper I will first summarize the results of several years' work on one specific class of mutants in the nematode, sensory mutants, work performed both in my laboratory and that of my colleagues Jim Lewis and Jonathan Hodgkin. Second, I will discuss frankly some of the difficulties and frustrations we have experienced in trying to interpret the effects of these specific mutants. Some of these difficulties illustrate problems endemic to genetic studies of development. Third, I will describe the more recent work performed in my labortory that is being directed toward genetic analysis of the structure and function of a
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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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[
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.