Early-Life Exposure to Methylmercury in Wildtype and pdr-1/parkin Knockout C. elegans

Abstract

We examined the impact of early-life exposure to methylmercury (MeHg) on Caenorhabditis elegans (C. elegans) pdr-1 mutants, addressing gene-environment interactions. We tested the hypothesis that early-life exposure to MeHg and knockout (KO) of pdr-1 (mammalian: parkin/PARK2) exacerbates MeHg toxicity and damage to the dopaminergic (DAergic) system. pdr-1KO worms showed increased lethality and decreased lifespan following MeHg exposure. Mercury (Hg) content, measured with Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) was increased in pdr-1KO worms compared to wildtype (N2) controls. 2′7′ dichlorodihydrofluorescein diacetate (H2DCF-DA) assay revealed a significant increase in reactive oxygen species (ROS) in both strains following MeHg exposure; however, while N2 worms showed an increase in skn-1 transcript levels following MeHg exposure, there was no difference in skn-1 induction in pdr-1KO worms. Dopamine-dependent behavioral analysis revealed an effect of MeHg on N2 wildtype worms, but no effect on pdr-1KO worms. Taken together, these results suggest that pdr-1KO worms are more sensitive to MeHg than wildtype worms, but MeHg does not exacerbate behavioral changes related to the absence of pdr-1.

Highly sensitive isotope-dilution liquid-chromatography–electrospray ionization–tandem-mass spectrometry approach to study the drug-mediated modulation of dopamine and serotonin levels in Caenorhabditis elegans

“…These mutants have an impaired DA biosynthesis and, likewise, the corresponding chromatogram lacks a clear DA signal. In fact, homogenates of cat-2 worms are not completely free of DA [33]. However, determined concentrations in our studies were between the LOD and LOQ.…”

“…After a five-minute acclimation period, the locomotion rate was assessed as the number of body-bends per 20 s, and data are presented as the change in body bends (body bends on food – body bends off food); analysis was carried out after coding of plates. Worms deficient in cat-2 were used as positive control since they are TH-deficient [33]. …”

Recent Advances in Mercury Research

“…Studies in Caenorhabditis elegans conducted by Martinez-Finley and colleagues have shown a latency period for neurodegeneration in combination with susceptibility of genetic background [41, 42]. The first study described the impact of early-life exposure to MeHg and knockdown of skn - 1 , the major stress-activated cytoprotective transcription factor, on dopaminergic (DAergic) neurodegeneration, mercury content, and stress reactivity in the nematode C. elegans .…”

“…Dopamine-dependent behavioral analysis revealed an effect of MeHg on N2 wild-type worms, but no effect on pdr - 1 KO worms. These results suggested that pdr - 1 KO worms were more sensitive to MeHg than wild-type worms, but MeHg did not exacerbate behavioral changes already present in pdr-1KOs, even after a period of latency [42]. …”

Early Exposure to Mercuric Chloride or Methylmercury Alters Zebrafish Embryo (Danio rerio) Development

“…Non-mammalian models that are used to study toxicity such as C. elegans (Martinez-Finley et al [25]) and Zebrafish (Danio rerio) (Carvalho et al [26]) are becoming more commonly used to study mechanisms of toxicity and as alternatives to mammalian animal testing. Some advantages of using zebrafish embryos (ZFEs) in toxicity assessment include: a transparent "shell" or chorion that encloses the developing ZFEs during early development; embryos whose tissues also are transparent early in development; rapid ex utero development; and the ability to directly and accurately deliver chemicals of interest to developing ZFEs [27][28][29].…”