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Caenorhabditis elegans is a free-living soil nematode, about 1 mm in length, that is found around the world. It is currently a common laboratory model for many aspects of cellular, developmental, and molecular biology. Its popularity comes from its transparency (allowing all nuclei to be followed in living animals at all stages of development), its anatomical simplicity (1000 cells), its small genome (100 Mbp), an invariant somatic cell lineage, ease of laboratory culture, rapid generation time, and a mode of reproduction which facilitates classical genetic analysis. An interested beginner needs only a petri plate, some Escherichia coli, and a stereo dissecting microscope to begin study of this fascinating creature.
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[
1993]
In the past 10 years, the remarkable discovery has been made that molecular mechanisms of development are conserved among all animals, and that many of the same molecular components appear in signal transduction pathways of all eukaryotes from yeast to man. This mechanistic conservation means that molecules can be studied in the organism in which their properties are most transparent; general principles or specific predictions made from work in one organism can subsequently be explored in other organisms. This chapter reviews aspects of nervous system development that have been studied using genetic approaches in two simple invertebrates, the fruit fly Drosophila melanogaster (herein referred to as Drosophila) and the soil nematode worm Caenorhabditis elegans (C. elegans). The nervous systems of both of these organisms are extremely simple compared to those of mammals....
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Programmed cell death is a common cell fate in most if not all multicellular organisms. Apoptosis, which will be used as a synonym for programmed cell death throughout this chapter, occurs extensively during development as well as during later life. The development of the nematode worm Caenorhabditis elegans provides a good example of the extensive use of programmed cell death.
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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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[
1987]
Vitellogenins of many insects, vertebrates, nematodes and sea urchins are very similar in size and amino acid composition. We have determined the nucleotide sequences of the genes that encode vitellogenins in nematodes (C. elegans) and sea urchins (S. purpuratus), and compared the deduced amino acid sequences to the published sequences of two vertebrate vitellogenins (X. laevis and G. gallus). This comparison demonstrated unequivocally that the nematode and vertebrate proteins are encoded by distant members of a single gene family. The less extensive sequence data available for the sea urchin gene indicates that this, too, may be a member of this family of genes, as may the vitellogenin genes of locust. On the other hand, we were unable to detect any similarity between these genes and the D. melanogaster yolk protein genes. Thus it appears that while nematodes, vertebrates, sea urchins and at least some insects utilize the same family of genes to encode vitellogenins, Drosophila uses a different gene family. All of the vitellogenin genes are regulated in a tissue-specific manner. They are expressed in the intestine in nematodes, in the liver in vertebrates, in the fat body in insects, and in the intestine and gonad in sea urchins. Their production is limited to adult females in all species except sea urchins, in which they are expressed by adults of both sexes. In nematodes we have identified two heptameric sequence elements repeated multiple times in all eleven of the vitellogenin genes sequenced. One of these elements is also present in the vertebrate promoters and has recently been shown to be required for transcriptional activation. All of the 5' ends of the vitellogenin mRNAs of nematodes, vertebrates and locust can be folded into potentially-stable secondary structures. We present evidence that these structures have been strongly selected for and presumably perform some function in regulation of vitellogenin production.
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[
1982]
Caenorhabditis elegans is a free-living, nonparasitic nematode. It is a self-fertilizing hermaphrodite. Males arise spontaneously by nondisjunction of X-chromosomes. Of all eukaryotic organisms C. elegans has probably been most extensively studied at the cellular level. Within 12 hours the fertilized egg develops into a young larva with 558 nuclei (560 in the male). During postembryonic development the animal proceeds through four larval stages increasing its number of nuclei to 959 (1,031 in the male) plus some 2,000 germ cells (about 1,000 in the male). The cell lineages from fertilization to adulthood have been completely analyzed in living embryos and animals. This and its well-established genetics (more than 300 genes have been mapped on the six linkage groups) make it a suitable model organism to study problems of gene action and development. Various techniques have been used to interfere with normal development (including laser-induced cell ablations) and to analyze development on the subcellular level (including recombinant DNA technology). The characteristic features of rigidly determined development, the low cell number, and the knowledge of cellular events should make it possible to identify molecular action in situ and relate it to the structure and
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[
1989]
Sperm motility usually refers to swimming motion propelled by a beating flagellum. In fact, the abundance and availability of flagellated sperm, particularly from sea urchins, have made these cells valuable models for studying all aspects of microtubule-based motility. There are, however, other types of sperm that lack flagella and must use alternative methods to reach oocytes. Among these are the amoeboid sperm of nematodes...
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[
WormBook,
2007]
Because of their free-living life cycle alternatives, Strongyloides and related nematode parasites may represent the best models for translating C. elegans science to the study of nematode parasitism. S. stercoralis, a significant pathogen of humans, can be maintained in laboratory dogs and gerbils. Biosafety precautions necessary for work with S. stercoralis, though unfamiliar to many C. elegans researchers, are straightforward and easily accomplished. Although specialized methods are necessary for large-scale culture of the free-living stages of S. stercoralis, small-scale cultures for experimental purposes may be undertaken using minor modifications of standard C. elegans methods. Similarly, the morphological similarities between C. elegans and the free-living stages of S. stercoralis allow investigational methods such as laser cell ablation and DNA transformation by gonadal microinjection to be easily adapted from C. elegans to S. stercoralis. Comparative studies employing these methods have yielded new insights into the neuronal control of the infective process in parasites and its similarity to regulation of dauer development in C. elegans. Furthermore, we have developed a practical method for transient transformation of S. stercoralis with vector constructs having various tissue- and cell-specific expression patterns and have assembled these into a modular vector kit for distribution to the community.
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[
WormBook,
2005]
C. elegans has emerged as a powerful genetic model organism in which to study synaptic function. Most synaptic proteins in the C. elegans genome are highly conserved and mutants can be readily generated by forward and reverse genetics. Most C. elegans synaptic protein mutants are viable affording an opportunity to study the functional consequences in vivo. Recent advances in electrophysiological approaches permit functional analysis of mutant synapses in situ. This has contributed to an already powerful arsenal of techniques available to study synaptic function in C. elegans. This review highlights C. elegans mutants affecting specific stages of the synaptic vesicle cycle, with emphasis on studies conducted at the neuromuscular junction.
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[
WormBook,
2007]
Acetylcholine is the major excitatory neurotransmitter at nematode neuromuscular junctions, and more than a third of the cells in the C. elegans nervous system release acetylcholine. Through a combination of forward genetics, drug-resistance selections, and genomic analysis, mutants have been identified for all of the steps specifically required for cholinergic function. These include two enzymes, two transporters, and a bewildering assortment of receptors. Cholinergic transmission is involved, directly or indirectly, in many C. elegans behaviors, including locomotion, egg laying, feeding, and male mating.