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[
2020]
Onchocerciasis, also known as the African river blindness, is the second most important cause of infectious blindness worldwide after trachoma. It is caused by the filarial nematode, <i>Onchocerca volvulus</i>, and transmitted by repeated bites of the vector, female black fly of the genus <i>Simulium damnosum</i>. The vector breeds in fast-flowing and oxygen-rich rivers in affected areas with transmission and disease prevalence usually stretching along these river basins and thereby the name river blindness.[1]Aside from blindness, onchocerciasis results in a troubling chronic dermatitis.[1]
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[
1977]
The workshop on nematodes presented current research from four laboratories on the development and physiology of C. elegans.
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Applications of, and investigations on lectins in nematology reflect the existing classification of nematodes according to their life-styles, i.e. free-living, plant-parasitic and animal-parasitic. In animal-parasitic nematodes, lectins have predominately been used to study the cuticle and its interaction between nematode and host. In plant-parasitic nematodes, investigations on the cuticle and amphid exudates have been predominant. Nematode-plant interactions on the other hand have attracted only minor attention. Ironically, however, the free-living nematodes in general, and the widely used model system Caenorhabditis elegans in particular, have been used very little for study of lectins, in spite of the many advantages offered by this organism as a genetic and an experimental model system.
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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.
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[
1990]
The free-living nematode Caenorhabditis elegans is a small and unpretentious organism. It may thrive unnoticed in the cabbage patch in your backyard or the flower pot on your balcony. In their natural habitat soil nematodes live in a thin film of water. In the laboratory C. elegans dwells on Petri dishes in the liquid film on the top of an agar layer, but can also be grown in liquid culture. As in other nematodes the liquid-filled body cavity (pseudocoelom) functions as a hydroskeleton. When the worm dries out, the hydroskeleton collapses and the animal inevitably dies. In a loose sense C. elegans may therefore be considered as a kind of aquatic animal. Because of this and because C. elegans is particularly well suited to the study of certain aspects of development, the following chapter is included in this book on Experimental Embryology of Aquatic Organisms. The intention of this contribution is to serve as an introduction and as a reference source rather than as a complete summary of present knowledge in the field. As indicated by the title, the review will focus on embryonic cell lineages, pattern formation in the embryo and the analysis of mutants affecting early
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[
2009]
This chapter focuses on the nematode (roundworm) Caenorhabditis elegans as an example of the phylum Nematoda. C. elegans provides a powerful genetic system for studying glycans during embryological development and in primitive organ systems.
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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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[
1984]
Developmental fates of blastomeres in early C. elegans embryos appear to be governed by internally segregating, cell-autonomous determinants. To ascertain whether previously described gut-lineage dterminants are nuclear or cytoplasmic, laser microsurgery was used to show that exposing the nucleus of a non-gut-precursor cell to gut-precursor cytoplasm can cause the progeny of the resulting hybrid cell to express gut-specific differentiation markers, supporting the view that the determinants are cytoplasmic. In attempts to obtain molecular probes for such determinants, a library of monoclonal antibodies to early embryonic antigens was generated and screened by immunofluorescence microscopy for antibodies reacting with lineage-specific components. Three of the antibodies react with cytoplasmic granules (P granules) that segregate specifically with the germ line in early cleavages and are found uniquely in germ-line cells throughout the life cycle. Experiments on unfertilized eggs, on mutant embryos with defects in early cleavage, and on normal embryos treated with various cytoskeletal inhibitors indicate that P-granule segregation depends upon fertilization and requires the function of actin microfilaments, but is independent of spindle and microtubule functions. Work on the biochemical nature and function of the P granules is in progress.
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[
1974]
The free-living nematode, Caenorhaditis briggsae, is being used in our laboratory to study the complex events associated with biological aging. Our approach to this problem involved first the defining of parameters characterizing senescence in this animal, and then evaluating the effects on these aging signs of a drug reported to have a modifying effect on some aspects of the aging processes. Reference in this report to this preparation, Gerovital H3 (2% procaine hydrochloride, 0.16% benzoic acid, 0.14% potassium metabisulfite, buffered to pH 3.3 from Rom-Amer Pharmaceuticals, Ltd., Beverly Hills, California) is by its active ingredient, "Procaine".
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Genetic analysis of C. elegans development has focused on developmental events that take place after hatching, during postembryonic development. After hatching with 558 cells, about 10% of these are blast cells that undergo further cell divisions (Fig. 1) to generate a total of 959 neurons, muscles, intestinal and hypodermal cells in the hermaphrodite and 1031 cells in the male. Like embryonic development (se Edgar, Chap. 19 this Vol.), the pattern of cell division and differentiation during C. elegans postembryonic development is nearly invariant and has been completely described. The cell lineage of wild-type, mutant, or laser-ablated animals can be determined by direct observation of development using Normarski optics. Because most cells during C. elegans postembryonic development generate unique patterns of descendents (though symmetries in the lineage exist), the cell lineage produced by a particular blast cell during development is a signature of that cell's identity. Any changes in cell identity, induce, for example, by laser ablation or neighboring cells or by mutation, can be recognized by a change in the lineage produced by that cell. By laser ablation, it has been shown that in many cases, that patterns of cell lineage executed by particular cells do not depend on their neighbors and instead reflect some intrinsic developmental program. On the other hand, the lineages of particular blast cells, for example, those that generate the hermaphrodite vulva, have been shown by laser ablation experiments to depend on interactions with their neighbors. Thus the pattern of cell divisions and differentiations that normally occur during C. elegans development depends on the ancestry of cells in some cases on their neighbors or positional signals in other cases. Two major goals of developmental genetic analysis in C. elegans have been to explain how genes couple cell lineage information to cell identity and to explain how genes control and mediate cell-cell interactions. As described below, this analysis has revealed molecular mechanisms for the generation of lineage asymmetry and for intercellular signaling that are general to perhaps all metazoans.