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[
Cell,
1998]
Many changes occur as an animal ages. To name a few, proteins become modified and cross-linked, somatic mutations accumulate, stress resistance decreases, and the probability of death increases. One reason for these changes is thought to be oxidative damage to macromolecules and lipid membranes, caused by superoxides and other free-radicals resulting from aerobic metabolism. In the somatic cells, this damage can be partially but never completely counteracted by mechanisms for elimination of free radicals as well as turnover and repair of macromolecules.
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[
Curr Biol,
1994]
Two genes that control dauer formation in the soil nematode Caenorhabditis elegans have direct effects on senescence.
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Trends Genet,
1994]
Recent studies reveal preliminary insights into the mechanisms of embryonic patterning in Caenorhabditis elegans. It appears that both embryonic axes and early blastomere fates are determined by a combination of segregating determinants and cell interactions, under the control of maternally expressed genes. Later in embryogenesis, some regional identities are specified by a group of homeotic selector genes homologous to the HOM-C clusters in other animals. Intervening stages of specification, which could link these two classes of genes in a regulatory hierarchy, are beginning to be investigated.
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[
Curr Biol,
1997]
Dosage compensation in Caenorhabditis elegans involves the sex-specific recruitment to the X chromosome of a protein complex, the nature of which suggests that there are mechanistic links between chromosome segregation and global transcriptional regulation.
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Front Genet,
2013]
Epigenetic regulatory mechanisms are increasingly appreciated as central to a diverse array of biological processes, including aging. An association between heterochromatic silencing and longevity has long been recognized in yeast, and in more recent years evidence has accumulated of age-related chromatin changes in Caenorhabditis elegans, Drosophila, and mouse model systems, as well as in the tissue culture-based replicative senescence model of cell aging. In addition, a number of studies have linked expression of transposable elements (TEs), as well as changes in the RNAi pathways that cells use to combat TEs, to the aging process. This review summarizes the recent evidence linking chromatin structure and function to aging, with a particular focus on the relationship of heterochromatin structure to organismal aging.
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[
Annual Review of Cell and Developmental Biology,
1997]
Most animal species exhibit left-right asymmetry in their body plans and show a strong bias for one handedness over the other. The mechanism of handedness choice, recognized as an intriguing problem over a century ago, is still a mystery. However, from recent advances in understanding when and how asymmetry arises in both invertebrates and vertebrates, developmental pathways for establishment and maintenance of left-right differences are beginning to take shape, and speculations can be made on the initial choice mechanism.
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[
Ciba Found Symp,
1991]
Embryos of the nematode Caenorhabditis elegans exhibit left-right asymmetry with an invariant handedness. The embryonic cell lineage is asymmetrical: although the animal is generally bilaterally symmetrical with only a few left-right asymmetries, many of its contralaterally analogous cells arise via different lineages on the two sides of the embryo. Larvae and adults also exhibit left-right asymmetries with a handedness that is normally invariant. The frequency of animals with opposite handedness was increased among the progeny of adults exposed to the mutagen ethyl methanesulphonate and among animals that developed from embryos treated in early cleavage with chitinase to destroy the egg shell. Reversal of embryonic handedness was accomplished directly by micromanipulation at the 6-cell stage, resulting in mirror-image but otherwise normal development into healthy, fertile animals with all the usual left-right asymmetries reversed. This demonstrates that (1) the handedness of cell positions in the 6-cell embryo dictates handedness throughout development; (2) at this stage the pair of anterior blastomeres on the right is equivalent to the pair on the left; and (3) the extensive differences in fates of lineally homologous cells on the two sides of the animal must be dictated by cellular interactions, most of which are likely to occur early in embryogenesis and appear to have been conserved in widely diverged nematode species.
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Results Probl Cell Differ,
1992]
Nematodes were first used to study embryogenesis more than 100 years ago, and this in part led to the concepts of cell-autonomous differentiation and localized cytoplasmic determinants. More recently, the techniques of genetics, experimental and descriptive embryology, and molecular biology have been combined to study the development of the small, free-living nematode Caenorhabditis elegans (Brenner 1974, 1988. This chapter focuses on embryonic development and is intended as a general overview of C. elegans embryogenesis, illustrating the experimental techniques available for this organism and the conclusions that can be drawn. Excellent reviews on postembryonic development (i.e. after hatching) in C. elegans and most other aspects of the worm's development, genetics and biology can be found in Wood (1988a). This book includes extensive appendices detailing techniques and anatomy and includes phenotypic descriptions of all mutants known at the time of publication. Other reviews of C. elegans embryogenesis can be found in Kemphues (1989), Wood (1988b), Schierenberg (1989) and Strome (1989).