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Can J Zool,
1982]
Dauerlarvae are reportedly adapted to withstand adverse environmental conditions. Current knowledge of the mechanisms underlying the unique characteristics of dauerlarvae is limited. This study characterizes superoxide dismutase (SODase) activity in several developmental stages of Caenorhabditis elegans (originally described by E. Maupas in 1900). Extracts of dauerlarvae have 17.1 units SODase per milligram protein, as compared with 4.3 and 3.8 units per milligram for obligate larvae and young adults, respectively. Since oxygen consumption in dauerlarvae is lower than that of young adults, the ratio of SODase to oxygen consumption is markedly higher in dauerlarvae than in young adults. The elevated SODase might contribute to an increased resistance to a variety of environmental stresses, including radiation. Furthermore, the elevation of this activity relative to metabolic rate could account for the long life-span of dauerlarvae.
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J Hered,
2010]
Caenorhabditis elegans is an androdioecious nematode with both hermaphrodites and males. Although males can potentially play an important role in avoiding inbreeding and facilitating adaptation, their existence is evolutionarily problematic because they do not directly generate offspring in the way that hermaphrodites do. This review explores how genetic, population genomic, and experimental evolution approaches are being used to address the role of males and outcrossing within C. elegans. Although theory suggests that inbreeding depression and male mating ability should be the primary determinants of male frequency, this has yet to be convincingly confirmed experimentally. Genomic analysis of natural populations finds that outcrossing occurs at low, but not negligible levels, and that observed patterns of linkage disequilibrium consistent with strong selfing may instead be generated by natural selection against outcrossed progeny. Recent experimental evolution studies suggest that males can be maintained at fairly high levels if populations are initiated with sufficient genetic variation and/or subjected to strong natural selection via a change in the environment. For example, as reported here, populations adapting to novel laboratory rearing and temperature regimes maintain males at frequencies from 5% to 40%. Laboratory and field results still await full reconciliation, which may be facilitated by identifying the loci underlying among-strain differences in mating system dynamics.
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J Exp Biol,
2007]
The preferred body temperature of ectotherms is typically inferred from the observed distribution of body temperatures in a laboratory thermal gradient. For very small organisms, however, that observed distribution might misrepresent true thermal preferences. Tiny ectotherms have limited thermal inertia, and so their body temperature and speed of movement will vary with their position along the gradient. In order to separate the direct effects of body temperature on movement from actual preference behaviour on a thermal gradient, we generate a null model (i.e. of non-thermoregulating individuals) of the spatial distribution of ectotherms on a thermal gradient and test the model using parameter values estimated from the movement of nematodes (Caenorhabditis elegans) at fixed temperatures and on a thermal gradient. We show that the standard lab strain N2, which is widely used in thermal gradient studies, avoids high temperature but otherwise does not exhibit a clear thermal preference, whereas the Hawaiian natural isolate CB4856 shows a clear preference for cool temperatures ( approximately 17 degrees C). These differences are not influenced substantially by changes in the starting position of worms in the gradient, the natal temperature of individuals or the presence and physiological state of bacterial food. These results demonstrate the value of an explicit null model of thermal effects and highlight problems in the standard model of C. elegans thermotaxis, showing the value of using natural isolates for tests of complex natural behaviours.
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J Vis Exp,
2018]
The number of new drugs identified by traditional, in vitro screens has waned, reducing the success of this approach in the search for new weapons to combat multiple drug resistance. This has led to the conclusion that researchers do not only need to find new drugs, but also need to develop new ways of finding them. Amongst the most promising candidate methods are whole-organism, in vivo assays that use high-throughput, phenotypic readouts and hosts that range from Caenorhabditis elegans to Danio rerio. These hosts have several powerful advantages, including dramatic reductions in false positive hits, as compounds that are toxic to the host and/or biounavailable are typically dropped in the initial screen, prior to costly follow up. Here we show how our assay has been used to interrogate host variation in the well-documented C. elegans-Pseudomonas aeruginosa liquid killing pathosystem. We also demonstrate several extensions of this well-worked out technique. For example, we are able to carry out high-throughput genetic screens using RNAi in 24- or 96-well plate formats to query host factors in this host-pathogen interaction. Using this assay, whole genome screens can be completed in only a few months, which can dramatically simplify the task of identifying drug targets, potentially without the need for laborious biochemical purification approaches. We also report here a variation of our method that substitutes the gram-positive bacterium Enterococcus faecalis for the gram-negative pathogen P. aeruginosa. Much as is the case for P. aeruginosa, killing by E. faecalis is time-dependent. Unlike previous C. elegans-E. faecalis assays, our assay for E. faecalis does not require preinfection, improving its safety profile and reducing the chances of contaminating liquid-handling equipment. The assay is highly robust, showing ~95% death rates 96 h post infection.
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J Biol Chem,
2022]
Virtually all age-related neurodegenerative diseases (NDs) can be characterized by the accumulation of proteins inside and outside the cell that are thought to significantly contribute to disease pathogenesis. One of the cell's primary systems for the degradation of misfolded/damaged proteins is the Ubiquitin Proteasome System (UPS), and its impairment is implicated in essentially all NDs. Thus, upregulating this system to combat NDs has garnered a great deal of interest in recent years. Various animal models have focused on stimulating 26S activity and increasing 20S proteasome levels, but thus far, none have targeted intrinsic activation of the 20S proteasome itself. Therefore, we constructed an animal model that endogenously expresses a hyperactive, open-gate proteasome in Caenorhabditis elegans (C. elegans). The gate-destabilizing mutation that we introduced into the nematode germline yielded a viable nematode population with enhanced proteasomal activity, including peptide, unstructured protein, and ubiquitin-dependent degradation activities. We determined these nematodes showed a significantly increased lifespan and substantial resistance to oxidative and proteotoxic stress but a significant decrease in fecundity. Our results show that introducing a constitutively active proteasome into a multicellular organism is feasible and suggests targeting the proteasome gating mechanism as a valid approach for future age-related disease research efforts in mammals.
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J Food Prot,
2003]
Free-living nematodes may harbor, protect, and disperse bacteria, including those ingested and passed in viable form in feces. These nematodes are potential vectors for human pathogens and may play a role in foodborne diseases associated with fruits and vegetables eaten raw. In this study, we evaluated the associations between a free-living soil nematode, Caenorhabditis elegans, and Escherichia coli, an avirulent strain of Salmonella Typhimurium, Listeria weshimeri, and Bacillus cereus. On agar medium, young adult worms quickly moved toward colonies of all four bacteria; over 90% of 3-day-old adult worms entered colonies within 16 min after inoculation. After 48 h, worms moved in and out of colonies of L. weshimeri and B. cereus but remained associated with E. coli and Salmonella Typhimurium colonies for at least 96 h. Young adult worms fed on cells of the four bacteria suspended in K medium. Worms survived and reproduced with the use of nutrients derived from all test bacteria, as determined for eggs laid by second-generation worms after culturing for 96 h. Development was slightly slower for worms fed gram-positive bacteria than for worms fed gram-negative bacteria. Worms that fed for 24 h on bacterial lawns formed on tryptic soy agar dispersed bacteria over a 3-h period when they were transferred to a bacteria-free agar surface. The results of the study suggest that C. elegans and perhaps other free-living nematodes are potential vectors for both gram-positive and gram-negative bacteria, including foodborne pathogens in soil.
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J Gerontol A Biol Sci Med Sci,
2011]
Many mutations that dramatically extend life span in model organisms come with substantial fitness costs. Although these genetic manipulations provide valuable insight into molecular modulators of life span, it is currently unclear whether life-span extension is unavoidably linked to fitness costs. To examine this relationship, we evolved a genetically heterogeneous population of Caenorhabditis elegans for 47 generations, selecting for early fecundity. We asked whether an increase in early fecundity would necessitate a decrease in longevity or late fecundity (antagonistic pleiotropy). Caenorhabditis elegans experimentally evolved for increased early reproduction and decreased late reproduction but suffered no total fitness or life-span costs. Given that antagonistic pleiotropy among these traits has been previously demonstrated in some cases, we conclude that the genetic constraint is not absolute, that is, it is possible to uncouple longevity from early fecundity using genetic variation segregating within and among natural populations.
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Development,
2021]
Swathi Arur is an Associate Professor for the Department of Genetics at the MD Anderson Cancer Center, USA, where she uses multidisciplinary approaches to understand female germline development and fertility. She has received numerous accolades, including the MD Anderson Distinguished Research Faculty Mentor Award in 2017. In 2020, she was elected to the American Association for the Advancement of Science (AAAS). Swathi joined the team at Development as an Academic Editor in 2020, and we met with her over Zoom to hear more about her life, her career and her love for <i>C. elegans</i>.