McHugh TD et al. (1994) J Helminthol "The migration and attrition of Strongyloides ratti in naive and sensitized rats."

McLaren DJ, Jenkins T, Greenwood R, McHugh TD

[J Helminthol, 1994]

Compressed organ autoradiography has been utilized to study the migration of the homogonic strain of Strongyloides ratti from the site of skin penetration to the gut. This transit is characterized by rapid disappearance of parasites from the cutaneous site of infection, followed by vascular dispersal throughout all organs investigated. For the first time, parasite migration in both naive and previously sensitized hosts is compared; the principal stations of migration are the same in the two groups although there is a quantitative difference in accumulation of parasites with time in these stations. Parasite attrition occurs in both groups of animals; however, in naive rats it is not manifest until day 20-25 post challenge, whereas in sensitized rats immune elimination occurs as early as 48 h post challenge.

McHugh TD et al. (1989) Parasitology "Strongyloides ratti: studies of cutaneous reactions elicited in naive and sensitized rats and of changes in surface antigenicity of skin-penetrating larvae."

McLaren DJ, McHugh TD, Jenkins T

[Parasitology, 1989]

This study provides the first quantitative assessment of the cutaneous reaction elicited in naive and sensitized rats by invading larvae of Strongyloides ratti. Parasites were identified in skin samples harvested from both naive and sensitized rats between 0.5 and 8 h following percutaneous infection, but were no longer visible at the site of invasion at 24 h. Mast cells, neutrophils, eosinophils and mononuclear cells recruited into the dermis in response to invading larvae were recorded and quantified. Cellular infiltrates were observed as early as 1 h post-invasion in naive/challenged skin, where total cell numbers were up to 3 times greater than in naive control tissue. Peak numbers of all cell types were recorded from 3 to 8 h in both naive/challenged and sensitized/challenged hosts. Interestingly, the reaction in sensitized/challenged rats was neither enhanced nor accelerated, a feature perhaps attributable to lack of recognition of parasite antigens by the host. This possibility was investigated by immunofluorescent labelling, which clearly demonstrated changes in the surface antigen profile of the parasite following penetration of the host skin both in vitro and in vivo. It is proposed that these changes in surface antigenicity constitute an evasive stratagem used by the parasite to deter the host from mounting a potentially lethal inflammatory response.

Bailey DC et al. (2017) Environ Toxicol Pharmacol "Chronic exposure to a glyphosate-containing pesticide leads to mitochondrial dysfunction and increased reactive oxygen species production in Caenorhabditis elegans."

Pressley AS, Denney RD, Snapp IB, Negga R, Burchfield SL, Traynor WL, Bailey DC, Fitsanakis VA, Todt CE

[Environ Toxicol Pharmacol, 2017]

Glyphosate-containing herbicides are among the most widely-used in the world. Although glyphosate itself is relatively non-toxic, growing evidence suggests that commercial herbicide formulations may lead to increased oxidative stress and mitochondrial inhibition. In order to assess these mechanisms in vivo, we chronically (24h) exposed Caenorhabditis elegans to various concentrations of the glyphosate-containing herbicide TouchDown (TD). Following TD exposure, we evaluated the function of specific mitochondrial electron transport chain complexes. Initial oxygen consumption studies demonstrated inhibition in mid- and high-TD concentration treatment groups compared to controls. Results from tetramethylrhodamine ethyl ester and ATP assays indicated reductions in the proton gradient and ATP levels, respectively. Additional studies were designed to determine whether TD exposure resulted in increased reactive oxygen species (ROS) production. Data from hydrogen peroxide, but not superoxide or hydroxyl radical, assays showed statistically significant increases in this specific ROS. Taken together, these data indicate that exposure of Caenorhabditis elegans to TD leads to mitochondrial inhibition and hydrogen peroxide production.

Negga R et al. (2011) Neurotoxicology "Exposure to Mn/Zn ethylene-bis-dithiocarbamate and glyphosate pesticides leads to neurodegeneration in Caenorhabditis elegans."

Fitsanakis VA, Negga R, Fields AS, Davis NS, Rudd DA, Hatfield HE, Valente AL, Justice AN

[Neurotoxicology, 2011]

Epidemiological evidence suggests positive correlations between pesticide usage and the incidence of Parkinson's disease (PD). To further explore this relationship, we used wild type (N2) Caenorhabditis elegans (C. elegans) to test the following hypothesis: Exposure to a glyphosate-containing herbicide (TD) and/or a manganese/zinc ethylene-bis-dithiocarbamate-containing fungicide (MZ) may lead to neurotoxicity. We exposed N2 worms to varying concentrations of TD or MZ for 30 min (acute) or 24h (chronic). To replicate agricultural usage, a third population was exposed to TD (acute) followed by MZ (acute). For acute TD exposure, the LC(50)=8.0% (r(2)=0.6890), while the chronic LC(50)=5.7% (r(2)=0.9433). Acute MZ exposure led to an LC(50)=0.22% (r(2)=0.5093), and chronic LC(50)=0.50% (r(2)=0.9733). The combined treatment for TD+MZ yielded an LC(50)=12.5% (r(2)=0.6367). Further studies in NW1229 worms, a pan-neuronally green fluorescent protein (GFP) tagged strain, indicated a statistically significant (p<0.05) and dose-dependent reduction in green pixel number in neurons of treated worms following each paradigm. This reduction of pixel number was accompanied by visual neurodegeneration in photomicrographs. For the dual treatment, Bliss analysis suggested synergistic interactions. Taken together, these data suggest neuronal degeneration occurs in C. elegans following treatment with environmentally relevant concentrations of TD or MZ.

McVey KA et al. (2016) Neurotoxicol Teratol "Exposure of C. elegans eggs to a glyphosate-containing herbicide leads to abnormal neuronal morphology."

Johnson MB, McVey KA, Negga R, Snapp IB, Fitsanakis VA, Pressley AS

[Neurotoxicol Teratol, 2016]

Recent data demonstrate that chronic exposure of Caenorhabditis elegans (C. elegans) to a high-use glyphosate-containing herbicide, Touchdown (TD), potentially damages the adult nervous system. It is unknown, however, whether unhatched worms exposed to TD during the egg stage show abnormal neurodevelopment post-hatching. Therefore, we investigated whether early treatment with TD leads to aberrant neuronal or neurite development in C. elegans. Studies were completed in three different worm strains with green fluorescent protein (GFP)-tagged neurons to facilitate visual neuronal assessment. Initially, eggs from C. elegans with all neurons tagged with GFP were chronically exposed to TD. Visual inspection suggested decreased neurite projections associated with ventral nerve cord neurons. Data analysis showed a statistically significant decrease in overall green pixel numbers at the fourth larval (L4) stage (*p<0.05). We further investigated whether specific neuronal populations were preferentially vulnerable to TD by treating eggs from worms that had all dopaminergic (DAergic) or -aminobutyric acid (GABAergic) neurons tagged with GFP. As before, green pixel number associated with these discrete neuronal populations was analyzed at multiple larval stages. Data analysis indicated statistically significant decreases in pixel number associated with DAergic, but not GABAergic, neurons (***p<0.001) at all larval stages. Finally, statistically significant decreases (at the first larval stage, L1) or increases (at the fourth larval stage, L4) in superoxide levels, a developmental signaling molecule, were detected (*p<0.05). These data suggest that early exposure to TD may impair neuronal development, perhaps through superoxide perturbation. Since toxic insults during development may late render individuals more vulnerable to neurodegenerative diseases in adulthood, these studies provide some of the first evidence in this model organism that early exposure to TD may adversely affect the developing nervous system.

Becker, S.F. et al. (2019) International Worm Meeting "You are what you experience : The impact of environnment on transdifferentiation."

Morin, M. - C., Jarriault, S., Medina Sanchez, J.D., Becker, S.F.

[International Worm Meeting, 2019]

Purpose: The balance between cellular identity maintenance and cellular plasticity (as the potential to change identity on a functional and morphological level) is a major challenge for organismal tissues. Uncontrolled cell fate changes can cause dysfunctional cellular behaviors such as cancer. Unraveling the mechanisms behind cell type conversion will further help to develop a safe environment for regenerative medicine. Here, we describe how chromatin remodeling as well as several external factors impacts on cellular identity and increase a cell's plasticity potential. Methods: We use a natural cell identity conversion in the worm to determine how a cell can change or maintain its identity. C. elegans rectal to neuronal Y-to-PDA transition is a bona fide robust transdifferentiation (Td) event: During L2 larval stage the rectal identity of the Y cell is erased completely, followed by redifferentiation into a fully functional motoneuron, named PDA. Results: We previously described a subset of essential factors driving Td initiation. We identified two novel positive regulators of Td: lin-15A and lin-56. In null mutants for these genes, PDA neurons are not made and Y cells remain epithelial. Genetic interactions suggest that these two genes act in a parallel pathway to the previously described "drivers" during Td initiation and that they antagonize a SynMuvB-based identity maintenance mechanism to "license" Td in the Y cell. Our data suggest that this brake is represented by a defined chromatin state, and genetic alterations of chromatin architecture are able to suppress lin-15A phenotype. Excitingly, we found that this suppression is phenocopied under different environmental conditions: in particular, starvation and caloric restriction decrease PDA defects. Our data point to a food signal mediated by IIS and TOR pathways impacting cellular plasticity. Conclusion: Our data suggest that Td initiation requires not only drivers TF but also "licensers" such as lin-15A and lin-56 that allow Td to occur by removing negative regulators and enabling chromatin remodelling, whereas several environmental conditions can bypass the need for the licensers, and thus, increase plasticity and allow transdifferentiation to occur.

Burchfield SL et al. (2018) Environ Toxicol Pharmacol "Acute exposure to a glyphosate-containing herbicide formulation inhibits Complex II and increases hydrogen peroxide in the model organism Caenorhabditis elegans."

Fitsanakis VA, Todt CE, Burchfield SL, Denney RD, Negga R, Bailey DC

[Environ Toxicol Pharmacol, 2018]

Glyphosate-based herbicides, such as Touchdown (TD) and Roundup, are among the most heavily-used herbicides in the world. While the active ingredient is generally considered non-toxic, the toxicity resulting from exposure to commercially-sold formulations is less clear. In many cases, cell cultures or various model organisms exposed to glyphosate formulations show toxicity and, in some cases, lethality. Using Caenorhabditis elegans, we assessed potential toxic mechanisms through which a highly-concentrated commercial formulation of TD promotes neurodegeneration. Following a 30-min treatment, we assayed mitochondrial electron transport chain function and reactive oxygen species (ROS) production. Initial oxygen consumption studies indicated general mitochondrial inhibition compared to controls (^*p<0.05). When Complex II activity was further assessed, inhibition was observed in all TD-treated groups (^*p<0.05). Complex IV activity, however, was not adversely affected by TD. This electron transport chain inhibition also resulted in reduced ATP levels (^*p<0.05). Furthermore, hydrogen peroxide levels, but not other ROS, were increased (^*p<0.05). Taken together, these data indicate that commercially-available formulations of TD may exert neurotoxicity through Complex II (succinate dehydrogenase) inhibition, decreased ATP levels, and increased hydrogen peroxide production.

Kriegeskorte A et al. (2014) MBio "Inactivation of thyA in Staphylococcus aureus attenuates virulence and has a strong impact on metabolism and virulence gene expression."

Kahl BC, Becker K, Lore NI, Baum C, Seggewiss J, Peters G, Neumann C, Hertel P, Liebau E, Drescher M, Block D, Bragonzi A, Proctor RA, Windmuller N, Kriegeskorte A, Mellmann A

[MBio, 2014]

Staphylococcus aureus thymidine-dependent small-colony variants (TD-SCVs) are frequently isolated from patients with chronic S. aureus infections after long-term treatment with trimethoprim-sulfamethoxazole (TMP-SMX). While it has been shown that TD-SCVs were associated with mutations in thymidylate synthase (TS; thyA), the impact of such mutations on protein function is lacking. In this study, we showed that mutations in thyA were leading to inactivity of TS proteins, and TS inactivity led to tremendous impact on S. aureus physiology and virulence. Whole DNA microarray analysis of the constructed thyA mutant identified severe alterations compared to the wild type. Important virulence regulators (agr, arlRS, sarA) and major virulence determinants (hla, hlb, sspAB, and geh) were downregulated, while genes important for colonization (fnbA, fnbB, spa, clfB, sdrC, and sdrD) were upregulated. The expression of genes involved in pyrimidine and purine metabolism and nucleotide interconversion changed significantly. NupC was identified as a major nucleoside transporter, which supported growth of the mutant during TMP-SMX exposure by uptake of extracellular thymidine. The thyA mutant was strongly attenuated in virulence models, including a Caenorhabditis elegans killing model and an acute pneumonia mouse model. This study identified inactivation of TS as the molecular basis of clinical TD-SCV and showed that thyA activity has a major role for S. aureus virulence and physiology. Importance: Thymidine-dependent small-colony variants (TD-SCVs) of Staphylococcus aureus carry mutations in the thymidylate synthase (TS) gene (thyA) responsible for de novo synthesis of thymidylate, which is essential for DNA synthesis. TD-SCVs have been isolated from patients treated for long periods with trimethoprim-sulfamethoxazole (TMP-SMX) and are associated with chronic and recurrent infections. In the era of community-associated methicillin-resistant S. aureus, the therapeutic use of TMP-SMX is increasing. Today, the emergence of TD-SCVs is still underestimated due to misidentification in the diagnostic laboratory. This study showed for the first time that mutational inactivation of TS is the molecular basis for the TD-SCV phenotype and that TS inactivation has a strong impact on S. aureus virulence and physiology. Our study helps to understand the clinical nature of TD-SCVs, which emerge frequently once patients are treated with TMP-SMX.

Zuryn S et al. (2014) Science "Transdifferentiation. Sequential histone-modifying activities determine the robustness of transdifferentiation."

White ER, Margueron R, Zuryn S, Morin MC, Jarriault S, Ahier A, Portoso M

[Science, 2014]

Natural interconversions between distinct somatic cell types have been reported in species as diverse as jellyfish and mice. The efficiency and reproducibility of some reprogramming events represent unexploited avenues in which to probe mechanisms that ensure robust cell conversion. We report that a conserved H3K27me3/me2 demethylase, JMJD-3.1, and the H3K4 methyltransferase Set1 complex cooperate to ensure invariant transdifferentiation (Td) of postmitotic Caenorhabditis elegans hindgut cells into motor neurons. At single-cell resolution, robust conversion requires stepwise histone-modifying activities, functionally partitioned into discrete phases of Td through nuclear degradation of JMJD-3.1 and phase-specific interactions with transcription factors that have conserved roles in cell plasticity and terminal fate selection. Our results draw parallels between epigenetic mechanisms underlying robust Td in nature and efficient cell reprogramming in vitro.

Biswas SN et al. (1996) Res Commun Mol Pathol Pharmacol "A phenomenological model describing pharyngeal pulsing in the nematode Caenorhabditis elegans anesthetized by alcohol."

Okada H, Shingai R, Biswas SN, Ebina Y

[Res Commun Mol Pathol Pharmacol, 1996]

The recovery process of the suppressed pharyngeal pulsation in the nematode has been investigated for several concentrations of a homologous primary alcohol series (CnH2n-1OH, n = 1,2,3). A mathematical model describing the time course of the recovery process is phenomenologically constructed by using two time constants of delay time tD and recovery time tau. The values of tD and tau are obtained by fitting the equation to experimental data. The obtained values increase with increasing alcohol concentration. To observe the characteristics of tD and tau against the alcohol of order n, the inverse of these time constants are computed at 25 v/v% concentration and plotted on a semi-logarithmic scale. The plot curves decrease non-linearly and are dissimilar to the well-known curves illustrating the importance of lipid solubility in the cell membrane in anesthetic phenomena.