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[
WormBook,
2014]
C. elegans detect and respond to diverse mechanical stimuli using neuronal circuitry that has been defined by decades of work by C. elegans researchers. In this WormMethods chapter, we review and comment on the techniques currently used to assess mechanosensory response. This methods review is intended both as an introduction for those new to the field and a convenient compendium for the expert. A brief discussion of commonly used mechanosensory assays is provided, along with a discussion of the neural circuits involved, consideration of critical protocol details, and references to the primary literature.
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[
1980]
The practical use of free-living nematodes for aging studies must overcome two problems. Not only must cultures begin with organisms of a similar age, but also reproduction must be prevented, or synchrony will be lost and the aging cultures will become contaminated with newborn orrganisms and will eventually revert to typical "mixed" cultures. The problem of obtaining uniformly small organisms to start cultures has been solved by the use of screens for Turbatrix aceti and the hatching of isolated egg masses for Caenorhabditis elegans. Subsequent reproduction is prevented by the use of the DNA inhibitor fluorodeoxyuridine, or by culturing the organisms at elevated temperatures. Another practical method for aging of T. aceti is the use of a repeated screening process that periodically removes small (young) organisms from the aging cultures.
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[
M S-Medecine Sciences,
1997]
The molecular pathways specifying cell fates during development are identified in the nematode Caeno-rhabditis elegans by the combination of genetic and molecular methods. For example, the differentiation of vulval precursor cells is induced by a signal similar to mammalian EGF, sent by the anchor cell of the gonad. This signal is received by a tyrosine kinase receptor and transmitted to the transcription factors in the nucleus through a very conserved molecular cascade. In mammals many components of this cascade, like Ras, are proto-oncogenes. At the cellular level, the reproducibility of C. elegans development and the possibility to selectively kill cells with a laser, allow the description of development in terms of cell interactions land asymmetric divisions. These developmental mechanisms can be ,compared in other nematode species: whereas molecular cascades are very conserved (even as far as mammals), modes of cell specification vary extensively (among nematodes).
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[
M S-Medecine Sciences,
1994]
In French.
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[
Med Trop (Mars),
2005]
Initial clinical trials in 1980 showed that ivermectin was remarkably effective against Onchocerca volvulus. Some 25 years after more than 50 million people are treated annually with Mectizan mainly within the framework of the African Programme for Onchocerciasis Control (APOC). This success has been possible thanks to Merck Mectizan Donation Program and to distribution through a novel strategy based on the strong involvement of endemic communities. In the last few years Mectizan has been used in combination with albendazole to control lymphatic filariasis on a large-scale basis in African countries. More recently ivermectin (under the tradename Stromectol) received market approval in France for treatment of gastrointestinal strongyloidiasis and scabies. Clinical trials are under way to evaluate the activity of ivermectin on nematodes (Loa loa, Mansonella sp., intestinal nematodes, cutaneous and visceral larva migrans) and ectoparasites (Pediculus humanus capitis, Phtirius pubis, Tunga penetrans, myiases). Trials are also ongoing to explain the mechanisms underlying the severe adverse events sometimes observed in patients presenting high Loa loa microfilaraemia and to develop preventive measures. Fundamental research will provide a better understanding of the mode of action of ivermectin at the molecular and cellular level, evaluate the risk of resistance of human parasites, and to determine the extent to which ivermectin could be used in association with other agents for the treatment of nonparasitic diseases.
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[
WormBook,
2005]
Basement membranes are thin, specialized extracellular matrices surrounding most tissues in all metazoans. The compositions and functions of basement membranes have generally been well conserved throughout the subkingdom. Genetic analyses of basement membrane components in C. elegans have provided insights into their assembly and functions during development. Immuno- or GFP-tagged localization studies have shown that basement membranes on different tissues, or even sub-regions of tissues, contain different sets of proteins or alternatively spliced isoforms of them. Several components, including laminin, perlecan, type IV collagen and possibly osteonectin/SPARC, are essential for completion of embryogenesis, being necessary for tissue organization and structural integrity. In contrast, type XVIII collagen and nidogen are not required for viability but primarily influence organization of the nervous system. All of these proteins, with the exception of nidogen and the addition of fibulin, have roles of varying degree in morphogenesis of the gonad. A major family of cellular receptors for basement membrane proteins, the integrins, have also been characterized in C. elegans. As one might expect, integrins have been shown to function in many of the same processes as their potential ligands, the basement membrane components. While much remains to be explored, studies of basement membranes in C. elegans have been highly informative and hold great promise for improving our understanding of how these structures are assembled and how they function in development.
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[
WormBook,
2005]
The use of Wnt ligands for signaling between cells is a conserved feature of metazoan development. Activation of Wnt signal transduction pathways upon ligand binding can regulate diverse processes including cell proliferation, migration, polarity, differentiation and axon outgrowth. A ''canonical'' Wnt signaling pathway has been elucidated in vertebrate and invertebrate model systems. In the canonical pathway, Wnt binding leads to the stabilization of the transcription factor beta-catenin, which enters the nucleus to regulate Wnt pathway target genes. However, Wnt binding also acts through beta-catenin-independent, noncanonical pathways, such as the planar cell polarity (PCP) pathway and a pathway involving Ca 2+ signaling. This chapter examines our current understanding of Wnt signaling and Wnt-mediated processes in the nematode C. elegans. Like other species, the C. elegans genome encodes multiple genes for Wnt ligands (five) and Wnt receptors (four frizzleds, one Ryk/Derailed). Unlike vertebrates or Drosophila, the C. elegans genome encodes three beta-catenin genes, which appear to have distinct functions in Wnt signaling and cell adhesion. Canonical Wnt signaling clearly exists in C. elegans, utilizing the beta-catenin BAR-1 . However, a noncanonical pathway utilizing the beta-catenin WRM-1 also exists, and to date a similar pathway has not been described in other species. Evidence for beta-catenin independent noncanonical Wnt signaling is currently limited. The role of Wnt signaling in over a dozen C. elegans developmental processes, including the regulation of cell fate, polarity and migration, is described.
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[
Science,
2005]
After anaphase onset, animal cells build an actomyosin contractile ring that constricts the plasma membrane to generate two daughter cells connected by a cytoplasmic bridge. The bridge is ultimately severed to complete cytokinesis. Myriad techniques have been used to identify proteins that participate in cytokinesis in vertebrates, insects, and nematodes. A conserved core of about 20 proteins are individually involved with cytokinesis in most animal cells. These components are found in the contractile ring, on the central spindle, within the RhoA pathway, and on vesicles that expand the membrane and sever the bridge. Cytokinesis involves additional proteins, but they, or their requirement in cytokinesis, are not conserved among animal cells.
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[
WormBook,
2006]
The C. elegans genome contains sequences similar to a large number of mammalian genes implicated in the assembly, processing, and modification of glycans. In recent years, spectacular progress has been made in developing and refining tools to obtain structural information with small amounts of material, increasing our understanding of glycan structural complexity in this organism. These approaches have revealed novel N- and O-glycan structures in C. elegans, as well as a high degree of conservation in glycosaminoglycan structure. In parallel, studies in which glycan structure is perturbed by genetic manipulation have begun to reveal the roles of specific carbohydrate moieties in developmental and physiological processes. This review summarizes recent work elucidating the fine structure of complex carbohydrates in C. elegans as well as genetic studies that have uncovered novel roles for complex carbohydrates in developmental processes.
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[
Science,
1992]
Oncogene researchers and developmental geneticists used to inhabit separate territories, but work on cellular signal transduction pathways is bringing them closer together.