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Changes in the molecular structure of mouse fetal astrocyte nucleosomes produced in vitro by methylmercuric chloride
Abstract:
The fluorescent probe N-(3-pyrene)maleimide, which specifically labels the cysteine residues of histone H3 within the nucleosome, was used to monitor changes in the nucleosomal structure of mouse fetal astrocytes exposed to varying concentrations of methylmercuric chloride. Methylmercuric chloride treatment (10 microM) for 6 hr produced a significant decrease in the degree of fluorescence of the probe. The decrease was much smaller following a 4-hr incubation period. These results correlate with recent observations showing that significant changes in the thymidine labeling index occur following 4-6 hr of exposure to methylmercury (MeHg). It is hypothesized that MeHg enters the cells during the growth phase and attaches to the protein moiety of the nucleosome in or near the cysteine groups of histone H3, thus diminishing the binding capacity of the fluorescent probe. Addition of a detergent (sodium dodecyl sulfate) resulted in only a small increase in the degree of fluorescence of the treated nucleosomes as compared to controls, showing that the interaction of MeHg with the nuclear proteins was not dissociated by detergent. In view of the strong interaction between DNA and the histone dimer H3-H4 and the potential importance of the latter in gene regulation, these results suggest an additional means by which MeHg may exert its toxic effects.
Insights
Methylmercury (MeHg) alters nucleosome structure by binding to histone H3 cysteine residues in mouse astrocytes. This binding reduces fluorescent probe signals, indicating MeHg
Area of Science:
- Toxicology
- Cell Biology
- Biochemistry
Background:
- Methylmercury (MeHg) is a potent neurotoxin.
- Nucleosomes are fundamental units of DNA packaging, influencing gene regulation.
- Histone H3 contains cysteine residues crucial for nucleosome structure and function.
Purpose of the Study:
- To investigate the effects of methylmercuric chloride on nucleosome structure in mouse fetal astrocytes.
- To understand the mechanism by which methylmercury interacts with nucleosomes.
Main Methods:
- Utilized the fluorescent probe N-(3-pyrene)maleimide to label histone H3 cysteine residues.
- Exposed mouse fetal astrocytes to varying concentrations of methylmercuric chloride.
- Monitored changes in fluorescence intensity to assess nucleosome structural alterations.
- Assessed the effect of sodium dodecyl sulfate on methylmercury-nucleosome interactions.
Main Results:
- Methylmercuric chloride treatment significantly decreased probe fluorescence, indicating structural changes in nucleosomes.
- The decrease in fluorescence was time-dependent, becoming more pronounced with longer exposure.
- Detergent treatment showed limited dissociation of methylmercury from nuclear proteins, suggesting strong binding.
Conclusions:
- Methylmercury binds to cysteine residues in histone H3 within nucleosomes.
- This interaction alters nucleosome structure and may interfere with gene regulation.
- The findings suggest a novel mechanism for methylmercury toxicity impacting nuclear processes.