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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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[
Methods Cell Biol,
1995]
Both the localization and distribution of nucleic acid sequences in genomes and in cells can be visualized by hybridization of labeled probe DNAs to cytological preparations of chromosomes or tissues. With the introduction of nonisotopically labeled nucleotides that could be incorporated into cloned DNAs by enzymatic methods in vitro, it became possible to detect the site of hybridization quickly using antibodies that recognized the modifying group on the nucleotides incorporated into the probe DNA. More recently, nucleotides labeled with a fluorescent molecule have been incorporated into probes by invitro enzymatic reactions and the site of hybridization can then be visualized directly. As fluorescence in situ hybridization provides a rapid and high-resolution method for mapping genes, it is being sued increasingly for mapping cloned DNAs to chromosomes and for the ordering of clones in large-scale genome projects. On the other hand, physically mapped clones can also be used to label chromosomes for analysis of such biological processes as chromosome segregation, pairing in meiosis, and interphase nuclear order. Nonisotopic methods of hybridization are also ideally suited to visualization of mRNA distributions in tissues, because the signal can be detected in thick specimens, in contrast to isotopic methods that require thin specimens for detection by autoradiography...
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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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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.
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[
1994]
Nematodes have been cultured continuously in the laboratory since 1944 when Margaret Briggs Gochnauer isolated and cultured the free-living hermaphroditic species Caenorhabditis briggsae. Work with C. briggsae and other rhabditid nematodes, C. elegans, Rhabditis anomala, and R. pellio, demonstrated the relative ease with which they could be cultured. The culturing techniques described here were developed for C. elegans, but are generally suitable (to varying degrees) for other free-living nematodes. Whereas much of the early work involved axenic culturing, most of these techniques are no longer in common use and are not included here. In the 1970s C. elegans became the predominant research model due to work by Brenner and co-workers on the genetics and development of this species. An adult C. elegans is about 1.5 mm long, and under optimal laboratory conditions has a life cycle of approximately 3 days. There are two sexes, males and self-fertile hermaphrodites, that are readily distinguishable as adults. The animals are transparent throughout the life cycle, permitting observation of cell divisions in living animals using differential interference microscopy. The complete cell lineage and neural circuitry have been determined and a large collection of behavioral and anatomical mutants have been isolated. C. elegans has six developmental stages: egg, four larval stages (L1-L4), and adult. Under starvation conditions or specific manipulations of the culture conditions a developmentally arrested dispersal stage, the dauer larva, can be formed as an alternative third larval stage. Many of the protocols included here and other experimental protocols have been summarized in "The Nematode Caenorhabditis elegans". We also include a previously unpublished method for long-term chemostat cultures of C. elegans. General laboratory culture conditions for nematode parasites of animals have been described, but none of these nematodes can be cultured in the laboratory through more than one life cycle. Marine nematodes and some plant parasites have been cultured xenically or with fungi. Laboratory cultivation of several plant parasites on Arabidopsis thaliana seedlings in agar petri plates has also been reported.