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[
1979]
Recombinant DNA methods have been used to characterize the genome of Caenorhabditis elegans. To determine if DNA rearrangements occur during somatic differentiation, fifteen randomly cloned Bam H1 fragments of somatic DNA were hybridized to Bam H1 digests of germ and somatic DNA's on Southern filters. In this way, 50 fragments representing 0.3% of the genome were compared and no size differences were detected. The DNA's of two interbreeding strains of C. elegans were also compared to determine the degree of evolutionary divergence. Fifteen percent of the fragments differed between the two strains. However, no differences could be found between the rDNA's. The DNA's of C. elegans and C. briggsae were compared and very little homology could be detected even though these species are morphologically very similar. The fragments that differ in size between the two interbreeding strains are being genetically mapped. These experiments suggest that non-random segregation of chromosomes might be occurring in
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[
1987]
Each year thousands of new chemicals are developed but the potential societal benefits are often unrealized or delayed due to the lack of toxicological data. In the past, chemicals were introduced into the environment with little or no toxicological testing. This has resulted in many examples where adverse effects to humans were seen only after years of exposure (e.g., asbestos, benzene, vinyl chloride). Because few chemicals are used as pure substances, the toxicity of mixtures is another problem. However, these potential chemical interactions are seldom evaluated. All of the above have increased the need for toxicological testing.
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[
1987]
Ascaris and several other parasitic nematodes undergo chromatin diminution in the somatic cell precursors of the early embryo. In 1910 Boveri hypothesized that the chromatin lost might include genes essential to the function of the germ line. We have cloned a germ line-specific cDNA which codes for the major sperm protein. Using this clone as a probe we found that these genes show no loss or rearrangement of DNA in somatic cells which have undergone chromatin diminution. Actin and a-tubulin genes from Ascaris are also unchanged following diminution. Ascaris and the free-living nematode Caenorhabditis elegans differ substantially in the numbers of actin and major sperm protein genes, in spite of conservation of gene
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[
1996]
At fertilization, the calm of oogenesis is broken, and the egg abruptly begins a flurry of activity. Many crucial steps - decisions concerning when and where to divide, specification of cell fates, and establishment of body axes - rely on materials the egg contains at that moment. In many animals, the first few hours of life proceed with little or no transcription. As a result, developmental regulation at these early stages is dependent on maternal cytoplasm, rather than the zygotic nucleus. The regulatory molecules accumulated during oogenesis might, in principle, be of any type, including RNA and protein. It is now clear that messenger RNAs present in the egg before fertilization (so-called maternal mRNAs) have a prominent role in early decisions. Viewed from this perspective, it is not surprising that oocytes and early embryos display an impressive array of posttrancriptional regulatory mechanisms, controlling mRNA stability, localization, and translation.
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[
2000]
At fertilization, the calm of oogenesis ends and the egg abruptly begins a flurry of activity. Many crucial steps - decisions concerning when and where to divide, specification of cell fates, and establishment of body axes - rely on materials the egg contains at that moment. In many animals, the first few hours of life proceed with little or no transcription. As a result, developmental regulation at these early stages is dependent on maternal cytoplasm rather than the zygotic nucleus. The regulatory molecules accumulated during oogenesis might, in principle, be of any type, including RNA and protein. It is clear that mRNAs present in the egg before fertilization - so-called maternal mRNAs - play a particularly prominent role in early decisions. Viewed from this perspective, it is not surprising that oocytes and early embryos display an impressive array of posttranscriptional regulatory mechanisms, controlling mRNA stability, localization, and translation.
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[
WormBook,
2005]
This chapter reviews analytical tools currently in use for protein classification, and gives an overview of the C. elegans proteome. Computational analysis of proteins relies heavily on hidden Markov models of protein families. Proteins can also be classified by predicted secondary or tertiary structures, hydrophobic profiles, compositional biases, or size ranges. Strictly orthologous protein families remain difficult to identify, except by skilled human labor. The InterPro and NCBI KOG classifications encompass 79% of C. elegans protein-coding genes; in both classifications, a small number of protein families account for a disproportionately large number of genes. C. elegans protein-coding genes include at least ~12,000 orthologs of C. briggsae genes, and at least ~4,400 orthologs of non-nematode eukaryotic genes. Some metazoan proteins conserved in other nematodes are absent from C. elegans. Conversely, 9% of C. elegans protein-coding genes are conserved among all metazoa or eukaryotes, yet have no known functions.
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The International Microgravity Laboratory #1 Spacelab mission was launched on 22-Jan-1992 for an 8-day mission. The Radiat experiment was one of 17 investigations which used the ESA Biorack on IML-1 and it had two objectives. The first objective was to isolate and characterize mutations induced by cosmic rays; the second was to assess the fidelity of development in 0-gravity over two consecutive generations. Two strategies were used to isolate mutations in a set of essential genes or a specific gene and to correlate the genetic events with the passage of charged particles. The results were isolation of 60 lethal mutations whose phenotypes are related to the local pattern of energy deposition. 12 mutations in the
unc-22 gene include large deletions as characterized by DNA hybridization studies. Development of nematodes proceeded through two consecutive generations with no obvious defects. Cytoplasmic determinants in embryos, nuclear location and symmetry of cellular anatomy were normal as were Mendelian segregation and recombination of
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[
1987]
Work in our laboratory over the past several years has focused on the nature of early determinative decisions in embryos of the free-living nematode Caenorhabditis elegans. Two of these decisions regard determination of sex and determination of the level of X-chromosome expression. C. elegans has two sexes, self-fertilizing hermaphrodites and males. Hermaphrodites normally have two X chromosomes, and males have only one (there is no Y chromosome). Genetic and molecular evidence suggest that C. elegans compensates for this difference in X dosage, not by X inactivation as in mammals, but rather by global regulation of the X chromosome as in Drosophila; that is, X-linked genes are expressed at a higher level per chromosome in 1X than 2X animals, so that levels of X expression are similar in the two sexes. Also as in Drosophila, the primary signal that dictates both sex determination and level of X expression in C. elegans is the ration of the number of X chromosomes to the number of sets of autosomes (X/A ratio) rather than the absolute number of X chromosomes.|
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[
1990]
Nematodes have been used as biological models of aging for some twenty years, and a large number of reviews have appeared both as a chapter in the previous edition of this handbook and in other sources. Major advantages and disadvantages in the use of nematodes as model organisms have been well reviewed. It is clear that for some purposes, such as the identification of genetic variants in length of life, which will be reviewed here, nematodes are an invaluable model. Genetic variants of Caenorhabditis elegans have recently been isolated that have life span extensions of more than 70%; these strains offer an exceptional new avenue for the dissection of aging processes. With the exception of dietary restriction and selectively bred long-lived strains of Drosophila melanogaster, there are no other techniques for lengthening life, thereby allowing the study of associated changes in other physiological systems. This chapter will concentrate on C. elegans and will review the genetic techniques used to study againg as well as methodological advances in other areas of C. elegans genetics. The possibilities for the study of physiological alterations associated with aging through the use of such genetic variants are not yet being widely exploited, leaving open a wide variety of potential research areas.
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[
1992]
In vertebrates, acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) are polymorphic enzymes presenting both globular and asymmetric forms. In invertebrates, only AChE has been characterized so far that presents a reduced molecular diversity. In insects for example the major molecular form of AChE is an amphiphilic dimeric form attached to the membrane through a glycolipid covalently linked at the C-terminus of each catalytic subunit. This AChE has a substrate specificity intermediate to those of mammalina AChE and BChE. A glycoplipid-anchored 7.5S from has also been observed in the trematode Schistosoma mansoni. Asymmetric forms have never been convincingly reported in invertebrates except in the more evolved animals such as Amphioxius. In the latter case also there is no BChE but AChE presents catalytic properties intermediate to those of vertebrate AChE and BChE. We are now interested in nematode AChE(s) for the following reasons: -several species are agricultural pest and it is important to get further informations on the target of potential nematicides; -it has been shown that at least three different genes code for AChE in Caenorhabditis elegans. It is therefore interesting to see whether the presence of multiple genes results in an increased molecular diversity, to define what are the structural characteristics of each gene product and finally to clone and sequence thee three genes for evolutionary relationships with the other members of the cholinesterase