The Relationship Between Reproductive Status and Metallothionein mRNA Expression in the Common Killifish, Fundulus heteroclitus

Abstract

Metallothionein (MT), a ubiquitously distributed cysteine-rich metal binding protein, is considered to play an essential role in the regulation of intracellular metals and may serve as a defense mechanism as well as a biomarker of environmental exposure to toxic metals. In this study, basal expression of MT mRNA was characterized in male and female killifish Fundulus heteroclitus during non-spawning and spawning seasons. Hepatic, gill, and intestinal MT mRNA (copy number per μg total RNA) was assessed by reverse-transcriptase polymerase chain reaction (RT-PCR) and electrochemiluminescence (ECL). There were no observed differences in MT mRNA expression between male and female killifish during either season. The median MT copy numbers for both non-spawning and spawning killifish decreased in the order of liver>intestine>gill. In addition, there were no significant differences in liver, gill and intestine tissue MT mRNA copy numbers within each season. However, a significant increase in gill and intestine MT mRNA induction was observed in spawning compared to non-spawning killifish (p<0.05). While these results indicate a reproductive seasonal difference in Fundulus basal MT expression, this difference was irrespective of sex. The results of this study demonstrate the variability of basal MT mRNA expression in three killifish tissues and confirm the need for further research prior to the use of MT mRNA as a biomarker of xenobiotic exposure in Fundulus heteroclitus.