Embryo Microinjection of Selenomethionine Reduces Hatchability and Modifies Oxidant Responsive Gene Expression in Zebrafish

J K Thomas,D M Janz

doi:10.1038/srep26520

Abstract

In previous studies we demonstrated that exposure to selenomethionine (SeMet) causes developmental toxicities in zebrafish (Danio rerio). The objectives of this study were to establish a dose-response relationship for developmental toxicities in zebrafish after embryo microinjection of Se (8, 16 or 32 μg/g dry mass of eggs) in the form of SeMet, and to investigate potential underlying mechanism(s) of SeMet-induced developmental toxicities. A dose-dependent increase in frequencies of mortality and total deformities, and reduced hatchability were observed in zebrafish exposed to excess Se via embryo microinjection. The egg Se concentration causing 20% mortality was then used to investigate transcript abundance of proteins involved in antioxidant protection and methylation. Excess Se exposure modified gene expression of oxidant-responsive transcription factors (nuclear factor erythroid 2-related factor nrf2a and nrf2b), and enzymes involved in cellular methylation (methionine adenosyltransferase mat1a and mat2ab) in zebrafish larvae. Notably, excess Se exposure up-regulated transcript abundance of aryl hydrocarbon receptor 2 (ahr2), a signalling pathway involved in the toxicity of dioxin-related compounds. Our findings suggest that oxidative stress or modification of methylation, or a combination of these mechanisms, might be responsible for Se-induced developmental toxicities in fishes.

Highlights

Sequence (5′–3′) F: CTTCAACGCTCAGGTCATCA R: CGGTCGATCTTCTCCTTGAG F: CTTCACCGAGAGCATCACAA R: GTTCGTCGGGTTGTTCATTT F: ACACACACCTGAAGCAGACG R: GGCATCATGAGATCAGTGGA F: CCTGCCCAACAGACTCTCTC R: CGTCTTTGTCCGACTGTTCA F: CCAGAGCCCTACACAAGCAT R: TCCTTAAGTGGACGGTTTGC F: GAAATACGTCCGTCCTGGAA R: CATAAGGGACACAGGGTCGT F: TGGTGCTTTGAAGATCATGC R: CTGAAACAGCACCAGGTCAC F: GGACTGGATGAAGGGTGACA R: GCCTCACAGTCGTTCTTTCC F: ATGCAGTTCTTGACGCACAC R: TGGTGTCTCGCACAATCTTC F: TGACCGTTCAGCTGCTTATG R: GGGACGGAGGTCAAAGTTCT F: TGCGACCAGATAAGTGATGC R: TCAAAGCCCTTGGTTGAGTC F: GATGCTCCCAATCCTTTGAA R: CAACCTTCTCCACCTCTCCA
Greater mortality was observed in early life stages of zebrafish from the 11.0, 18.7 and 29.3 μg Se/g d.m. treatment groups when compared to controls (p < 0.05; Fig. 1)
The present SeMet embryo microinjection study was conducted with the intention to mimic maternal Se exposure, and was used to explore mechanisms of Se-induced toxicities in early life stages of zebrafish

Summary

Introduction

Sequence (5′–3′) F: CTTCAACGCTCAGGTCATCA R: CGGTCGATCTTCTCCTTGAG F: CTTCACCGAGAGCATCACAA R: GTTCGTCGGGTTGTTCATTT F: ACACACACCTGAAGCAGACG R: GGCATCATGAGATCAGTGGA F: CCTGCCCAACAGACTCTCTC R: CGTCTTTGTCCGACTGTTCA F: CCAGAGCCCTACACAAGCAT R: TCCTTAAGTGGACGGTTTGC F: GAAATACGTCCGTCCTGGAA R: CATAAGGGACACAGGGTCGT F: TGGTGCTTTGAAGATCATGC R: CTGAAACAGCACCAGGTCAC F: GGACTGGATGAAGGGTGACA R: GCCTCACAGTCGTTCTTTCC F: ATGCAGTTCTTGACGCACAC R: TGGTGTCTCGCACAATCTTC F: TGACCGTTCAGCTGCTTATG R: GGGACGGAGGTCAAAGTTCT F: TGCGACCAGATAAGTGATGC R: TCAAAGCCCTTGGTTGAGTC F: GATGCTCCCAATCCTTTGAA R: CAACCTTCTCCACCTCTCCA. The first proposed mechanism of Se-induced developmental toxicities is altered protein function, which is due to non-specific insertion of SeMet in place of the essential amino acid methionine (Met) during protein synthesis[16,17,18]. Since both SeMet and Met have similar physico-chemical properties, SeMet is inserted into proteins in an unregulated, dose-dependent fashion[19]. Since vast information is available on the developmental biology and genome of zebrafish, both developmental and mechanistic toxicological studies can be carried out in this fish species[27,28]

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Conclusion