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Published on: June 25, 2015
Tissue-restricted expression of Nrf2 and its target genes in zebrafish with gene-specific variations in the induction
Hitomi Nakajima1, Yaeko Nakajima-Takagi, Tadayuki Tsujita
1Institute of Basic Medical Sciences, Graduate School of Comprehensive Human Sciences, University of Tsukuba, Tsukuba, Japan.
Abstract:
The Keap1-Nrf2 system serves as a defense mechanism against oxidative stress and electrophilic toxicants by inducing more than one hundred cytoprotective proteins, including antioxidants and phase 2 detoxifying enzymes. Since induction profiles of Nrf2 target genes have been studied exclusively in cultured cells, and not in animal models, their tissue-specificity has not been well characterized. In this paper, we examined and compared the tissue-specific expression of several Nrf2 target genes in zebrafish larvae by whole-mount in situ hybridization (WISH). Seven zebrafish genes (gstp1, mgst3b, prdx1, frrs1c, fthl, gclc and hmox1a) suitable for WISH analysis were selected from candidates for Nrf2 targets identified by microarray analysis. Tissue-restricted induction was observed in the nose, gill, and/or liver for all seven genes in response to Nrf2-activating compounds, diethylmaleate (DEM) and sulforaphane. The Nrf2 gene itself was dominantly expressed in these three tissues, implying that tissue-restricted induction of Nrf2 target genes is defined by tissue-specific expression of Nrf2. Interestingly, the induction of frrs1c and gclc in liver and nose, respectively, was quite low and that of hmox1a was restricted in the liver. These results indicate the existence of gene-specific variations in the tissue specificity, which can be controlled by factors other than Nrf2.
Insights
The Keap1-Nrf2 system protects against oxidative stress. Zebrafish studies reveal Nrf2 target genes are tissue-specifically induced in the nose, gills, and liver, primarily driven by Nrf2 expression in these tissues.
Area of Science:
- Molecular Biology
- Toxicology
- Zebrafish Model Systems
Background:
- The Keap1-Nrf2 pathway is crucial for cellular defense against oxidative stress and toxicants.
- Nrf2 regulates over 100 cytoprotective proteins, including antioxidants and phase 2 detoxifying enzymes.
- Tissue-specific expression of Nrf2 target genes remains poorly understood due to limited studies in animal models.
Purpose of the Study:
- To investigate and compare the tissue-specific expression patterns of Nrf2 target genes in zebrafish larvae.
- To determine if tissue-specific induction is solely dependent on Nrf2 expression levels.
Main Methods:
- Whole-mount in situ hybridization (WISH) was employed to analyze gene expression in zebrafish larvae.
- Seven candidate Nrf2 target genes were selected based on microarray analysis.
- Zebrafish were treated with Nrf2-activating compounds: diethylmaleate (DEM) and sulforaphane.
Main Results:
- All seven selected Nrf2 target genes (gstp1, mgst3b, prdx1, frrs1c, fthl, gclc, hmox1a) showed tissue-restricted induction in the nose, gill, and/or liver.
- Nrf2 gene expression was predominantly observed in these same three tissues, suggesting Nrf2's role in tissue-specific induction.
- Specific genes exhibited unique induction patterns: low induction for frrs1c (liver) and gclc (nose), and liver-restricted induction for hmox1a.
- Gene-specific variations in tissue specificity were observed, indicating regulation by factors beyond Nrf2.
Conclusions:
- Nrf2 expression in specific tissues like the nose, gills, and liver dictates the tissue-restricted induction of its target genes.
- The study highlights gene-specific regulatory mechanisms that contribute to variations in tissue specificity for Nrf2 targets.
- These findings underscore the complexity of the Keap1-Nrf2 pathway's regulation in vivo.
