Induction and inhibition of oocyte maturation by EDCs in zebrafish

Toshinobu Tokumoto,Mika Tokumoto,Yoshitaka Nagahama

doi:10.1186/1477-7827-3-69

Abstract

BackgroundOocyte maturation in lower vertebrates is triggered by maturation-inducing hormone (MIH), which acts on unidentified receptors on the oocyte surface and induces the activation of maturation-promoting factor (MPF) in the oocyte cytoplasm. We previously described the induction of oocyte maturation in fish by an endocrine-disrupting chemical (EDC), diethylstilbestrol (DES), a nonsteroidal estrogen.MethodsIn this study, stimulatory and inhibitory effects of EDCs and natural steroids on oocyte maturation were examined in zebrafish. For effective agents, some details about the mechanism in induction or inhibition of maturation were examined. Possible groups of DES interacting with the MIH receptor are discussed based on relative potency of steroids to induce maturation.ResultsAmong agents tested, tamoxifen (TAM) and its metabolite 4-hydroxytamoxifen (4-OHT) showed stimulatory activity similar to DES. The time courses of the change in germinal vesicle breakdown and an intracellular molecular event (the synthesis of cyclin B) induced by TAM were indistinguishable from those induced by MIH. In contrast, pentachlorophenol (PCP) had a potent inhibitory effect on MIH-induced oocyte maturation. PCP inhibited not only MIH-induced maturation but also DES- and TAM-induced maturation. Methoxychlor also inhibited maturation when oocytes were pre-treated with this agent.ConclusionThese results suggest that EDCs act as agonists or antagonists in the induction of oocyte maturation in fish.

Highlights

Oocyte maturation in lower vertebrates is triggered by maturation-inducing hormone (MIH), which acts on unidentified receptors on the oocyte surface and induces the activation of maturation-promoting factor (MPF) in the oocyte cytoplasm
These results suggest that endocrine-disrupting chemical (EDC) act as agonists or antagonists in the induction of oocyte maturation in fish
Oocyte maturation in fish is triggered by MIH, which acts on receptors located on the oocyte membrane and induces the activation of MPF in the oocyte cytoplasm [2]

Summary

Introduction

Oocyte maturation in lower vertebrates is triggered by maturation-inducing hormone (MIH), which acts on unidentified receptors on the oocyte surface and induces the activation of maturation-promoting factor (MPF) in the oocyte cytoplasm. Several factors responsible for the regulation of meiotic maturation in fish oocytes have been identified. These include the isolation and characterization of a fish maturation-inducing hormone (MIH) and the components of maturation-promoting factor (MPF) (cdc, the catalytic subunit, and cyclin B, the regulatory subunit) [1]. Oocyte maturation in fish is triggered by MIH, which acts on receptors located on the oocyte membrane and induces the activation of MPF in the oocyte cytoplasm [2]. Two types of mPRs, α and β, were identified [8]. 17α, 20β-DHP has been shown to induce oocyte maturation by stimulating the de novo synthesis of cyclin B, a regulatory subunit of MPF [9]

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Discussion

Conclusion