Toxicogenomic analysis of Caenorhabditis elegans reveals novel genes and pathways involved in the resistance to cadmium toxicity

Global analysis of the transcriptional response to cadmium exposure in Caenorhabditis elegans reveals roles for genes involved in cellular trafficking, metabolic processes and proteolysis, and for the signaling protein KEL-8

Caenorhabditis elegans generates biologically relevant levels of genotoxic metabolites from aflatoxin B1 but not benzo[a]pyrene in vivo

Author Posting. © The Authors, 2010. This is the author's version of the work. It is posted here by permission of Oxford University Press for personal use, not for redistribution. The definitive version was published in Toxicological Sciences 118 (2010): 444-453, doi:10.1093/toxsci/kfq295.There is relatively little information regarding the critical xenobiotic-metabolizing cytochrome P450 (CYP) enzymes in Caenorhabditis elegans, despite this organism’s increasing use as a model in toxicology and pharmacology. We carried out experiments to elucidate the capacity of C. elegans to metabolically activate important promutagens via CYPs. Phylogenetic comparisons confirmed an earlier report indicating a lack of CYP1 family enzymes in C. elegans. Exposure to aflatoxin B1 (AFB1), which is metabolized in mammals by CYP1, CYP2, and CYP3 family enzymes, resulted in significant DNA damage in C. elegans. However, exposure to benzo[a]pyrene (BaP), which is metabolized in mammals by CYP1 family enzymes only, produced no detectable damage. To further test whether BaP exposure caused DNA damage, the toxicities of AFB1 and BaP were compared in nucleotide excision repair-deficient (xpa-1) and - proficient (N2) strains of C. elegans. Exposure to AFB1 inhibited growth more in xpa-1 than N2 nematodes, but the growth-inhibitory effects of BaP were indistinguishable in the two strains. Finally, a CYP-NADPH reductase- deficient strain (emb-8) of C. elegans was found to be more resistant to the growth inhibitory effect of AFB1 exposure than N2, confirming that the AFB1- mediated growth inhibition resulted from CYP-mediated metabolism. Together, these results indicate that C. elegans lacks biologically significant CYP1 family-mediated enzymatic metabolism of xenobiotics. Interestingly, we also found that xpa-1 nematodes were slightly more sensitive to chlorpyrifos than were wild-type. Our results highlight the importance of considering differences between xenobiotic metabolism in C. elegans and mammals when using this alternative model in pharmaceutical and toxicological research.This work was supported in part by NIH R21 NS065468 (JNM); the National Toxicology Program Z01ES102046 (WAB), the Intramural Research Program of the National Institute of Environmental Health Sciences Z01ES102045 (JHF). JVG was supported by NIH Grants to John Stegeman (R01-ES015912, and the Superfund Basic Research Program at Boston University 5- P42-ES007381)

Decline of nucleotide excision repair capacity in aging Caenorhabditis elegans

Repair of UVC-induced DNA damage in Caenorhabditis elegans is similar kinetically and genetically to repair in humans, and it slows significantly in aging C. elegans

A Discrete Time Model for the Analysis of Medium-Throughput C. elegans Growth Data

BACKGROUND: As part of a program to predict the toxicity of environmental agents on human health using alternative methods, several in vivo high- and medium-throughput assays are being developed that use C. elegans as a model organism. C. elegans-based toxicological assays utilize the COPAS Biosort flow sorting system that can rapidly measure size, extinction (EXT) and time-of-flight (TOF), of individual nematodes. The use of this technology requires the development of mathematical and statistical tools to properly analyze the large volumes of biological data. METHODOLOGY/PRINCIPAL FINDINGS: Findings A Markov model was developed that predicts the growth of populations of C. elegans. The model was developed using observations from a 60 h growth study in which five cohorts of 300 nematodes each were aspirated and measured every 12 h. Frequency distributions of log(EXT) measurements that were made when loading C. elegans L1 larvae into 96 well plates (t = 0 h) were used by the model to predict the frequency distributions of the same set of nematodes when measured at 12 h intervals. The model prediction coincided well with the biological observations confirming the validity of the model. The model was also applied to log(TOF) measurements following an adaptation. The adaptation accounted for variability in TOF measurements associated with potential curling or shortening of the nematodes as they passed through the flow cell of the Biosort. By providing accurate estimates of frequencies of EXT or TOF measurements following varying growth periods, the model was able to estimate growth rates. Best model fits showed that C. elegans did not grow at a constant exponential rate. Growth was best described with three different rates. Microscopic observations indicated that the points where the growth rates changed corresponded to specific developmental events: the L1/L2 molt and the start of oogenesis in young adult C. elegans. CONCLUSIONS: Quantitative analysis of COPAS Biosort measurements of C. elegans growth has been hampered by the lack of a mathematical model. In addition, extraneous matter and the inability to assign specific measurements to specific nematodes made it difficult to estimate growth rates. The present model addresses these problems through a population-based Markov model

Application of a Mathematical Model to Describe the Effects of Chlorpyrifos on Caenorhabditis elegans Development

The nematode Caenorhabditis elegans is being assessed as an alternative model organism as part of an interagency effort to develop better means to test potentially toxic substances. As part of this effort, assays that use the COPAS Biosort flow sorting technology to record optical measurements (time of flight (TOF) and extinction (EXT)) of individual nematodes under various chemical exposure conditions are being developed. A mathematical model has been created that uses Biosort data to quantitatively and qualitatively describe C. elegans growth, and link changes in growth rates to biological events. Chlorpyrifos, an organophosphate pesticide known to cause developmental delays and malformations in mammals, was used as a model toxicant to test the applicability of the growth model for in vivo toxicological testing.L1 larval nematodes were exposed to a range of sub-lethal chlorpyrifos concentrations (0-75 microM) and measured every 12 h. In the absence of toxicant, C. elegans matured from L1s to gravid adults by 60 h. A mathematical model was used to estimate nematode size distributions at various times. Mathematical modeling of the distributions allowed the number of measured nematodes and log(EXT) and log(TOF) growth rates to be estimated. The model revealed three distinct growth phases. The points at which estimated growth rates changed (change points) were constant across the ten chlorpyrifos concentrations. Concentration response curves with respect to several model-estimated quantities (numbers of measured nematodes, mean log(TOF) and log(EXT), growth rates, and time to reach change points) showed a significant decrease in C. elegans growth with increasing chlorpyrifos concentration.Effects of chlorpyrifos on C. elegans growth and development were mathematically modeled. Statistical tests confirmed a significant concentration effect on several model endpoints. This confirmed that chlorpyrifos affects C. elegans development in a concentration dependent manner. The most noticeable effect on growth occurred during early larval stages: L2 and L3. This study supports the utility of the C. elegans growth assay and mathematical modeling in determining the effects of potentially toxic substances in an alternative model organism using high-throughput technologies

Race, circulation, and the city: the case of the Chicago city sticker controversy

The city sticker controversy began when an anonymous, openly racist blog accused a Latino boy of smuggling gang imagery into his contest-winning design for the 2012 Chicago vehicle sticker. It continued when mainstream media outlets repeatedly cited the blog’s accusations without acknowledging its racism. I argue that a form of circulation that contains bodies of color and promotes the mobility of other bodies helped to secure the credibility of the blog’s claims, consolidating the association of bodies of color with gang violence. I explore the relationships among the processes and practices of urban circulation, race, digital media, and mainstream media

A Rumble in the Tummy: The Overlap between Child Hunger and Obesity Rates

In the US, many studies have found evidence that increased obesity may be related to food insecurity – defined as “limited or uncertain availability of nutritionally adequate and safe foods or limited or uncertain ability to acquire acceptable foods in socially acceptable ways” (Franklin et al. 2012). This finding is often described as a paradox as food insecurity is due to inadequate resources to obtain food while obesity results from overconsumption (Dinour et al. 2007). While this relationship has been fairly constant among adult women in the U.S., associations among children and adolescents are much less consistent, for reasons which are unclear (Franklin et al. 2012). With the substantial and rising prevalence of both child obesity and food insecurity, a better understanding of the mechanisms and pathways underlying this relationship may influence the effectiveness of policies and programs designed to combat these issues. The aims of this policy brief are to: (1) Describe the links and possible mediators between food insecurity and child obesity; (2) Explore potential approaches to decrease food insecurity and child obesity; and (3) Identify policy implications and areas of future research to minimize the contribution of food insecurity on child obesity.Master of Public Healt

Effects of genetic mutations and chemical exposures on Caenorhabditis elegans feeding: evaluation of a novel, high-throughput screening assay.

Government agencies have defined a need to reduce, refine or replace current mammalian-based bioassays with testing methods that use alternative species. Invertebrate species, such as Caenorhabditis elegans, provide an attractive option because of their short life cycles, inexpensive maintenance, and high degree of evolutionary conservation with higher eukaryotes. The C. elegans pharynx is a favorable model for studying neuromuscular function, and the effects of chemicals on neuromuscular activity, i.e., feeding. Current feeding methodologies, however, are labor intensive and only semi-quantitative.Here a high-throughput assay is described that uses flow cytometry to measure C. elegans feeding by determining the size and intestinal fluorescence of hundreds of nematodes after exposure to fluorescent-labeled microspheres. This assay was validated by quantifying fluorescence in feeding-defective C. elegans (eat mutants), and by exposing wild-type nematodes to the neuroactive compounds, serotonin and arecoline. The eat mutations previously determined to cause slow pumping rates exhibited the lowest feeding levels with our assay. Concentration-dependent increases in feeding levels after serotonin exposures were dependent on food availability, while feeding levels decreased in arecoline-exposed nematodes regardless of the presence of food. The effects of the environmental contaminants, cadmium chloride and chlorpyrifos, on wild-type C. elegans feeding were then used to demonstrate an application of the feeding assay. Cadmium exposures above 200 microM led to a sharp drop in feeding levels. Feeding of chlorpyrifos-exposed nematodes decreased in a concentration-dependent fashion with an EC(50) of 2 microM.The C. elegans fluorescence microsphere feeding assay is a rapid, reliable method for the assessment of neurotoxic effects of pharmaceutical drugs, industrial chemicals or environmental agents. This assay may also be applicable to large scale genetic or RNAi screens used to identify genes that are necessary for the development or function of the pharynx or other neuromuscular systems