The effect of methylmercury exposure on early central nervous system development in the zebrafish (Danio rerio) embryo

Abstract

Much attention is focused on environmental contamination by heavy metals. The heavy metal mercury is found worldwide and is ranked number 3 on the Comprehensive Environmental Response, Compensation and Liability Act substance list. We examined the effect of low-level methylmercury exposure on central nervous system development of wild-type zebrafish embryos (ZFEs) of the AB strain because methylmercury is the most common form of mercury to which humans are exposed in the environment. ZFEs were exposed to nine different concentrations of methylmercury [0 (negative control), 5, 10, 50, 80, 100, 200, 500 and 1000 parts per billion (μg l(-1) )] starting at 6 h post-fertilization, which is the time the neural tube is first beginning to form. ZFEs were exposed to 2% ethanol as positive controls (100% embryonic death). ZFEs were assessed at 30, 54, 72 and 96 h post-fertilization for changes in embryonic development, mortality, time of hatching and morphological deformities. No abnormalities were observed in ZFEs exposed to 5 μg l(-1) methylmercury. The time of hatching from the chorion was delayed in ZFEs exposed to methylmercury concentrations of 50 μg l(-1) or higher. Significantly more ZFEs exposed to 0, 5 or 10 μg l(-1) methylmercury successfully completed hatching compared with ZFEs exposed to 50 μg l(-1) or higher methylmercury. ZFEs exposed to more than 200 μg l(-1) methylmercury exhibited 100% embryonic mortality. The rate of cell proliferation within the neural tube was significantly decreased in embryos exposed to 10, 50 and 80 μg l(-1) methylmercury and there were no differences between these doses.

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

“…Previous studies of effects of methyl mercury from our lab support these observations [45,53]. Kimmel et al (1995) defined seven distinct periods of zebrafish development between fertilization (0 h post fertilization or hpf) and initiation of the early larval period.…”

“…These morphological changes have been described in greater detail in Hassan et al [45]. ZFEs exposed to 0, 10 and 50 µg/L methyl mercury all exhibited normal spontaneous movements at 30 hpf, but ZFEs exposed to 80 µg/L methyl mercury showed little to no spontaneous movement (data not shown).…”

“…We used an antibody to Proliferating Cell Nuclear Antigen (PCNA) to label proliferating neural tube cells in ZFEs exposed to mercuric chloride. This same procedure was performed previously in this lab for ZFEs exposed to methyl mercury [45].…”

“…Previous investigations in this laboratory examined the effects of different doses of methyl mercury on mortality, hatching, body length and eye area in ZFEs [45,53]. These investigations determined that the lethal concentration of methyl mercury is 200 µg/L and greater for ZFEs exposed for 24 h and exposure to concentrations of 50 µg/L methyl mercury and greater significantly delayed ZFEs from hatching out of their chorion.…”

Zebrafish as a Model for Developmental Neurotoxicity Assessment: The Application of the Zebrafish in Defining the Effects of Arsenic, Methylmercury, or Lead on Early Neurodevelopment

“…Hassan et al [193] observed a significant reduction of cellular proliferation occurring in the neural tube of zebrafish developmentally exposed to 10, 50, or 80 µg/L (≈0.4 µM) MeHg at 30 hpf using PCNA staining. Cuello et al [194] investigated the effects of MeHg exposure on zebrafish development at the protein level using iTRAQ (isobaric tags for relative and absolute quantification).…”