Induction and inhibition of oocyte maturation by EDCs in zebrafish.
BACKGROUND
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. We previously described the induction of oocyte maturation in fish by an endocrine-disrupting chemical (EDC), diethylstilbestrol (DES), a nonsteroidal estrogen.


METHODS
In 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.


RESULTS
Among 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.


CONCLUSIONS
These results suggest that EDCs act as agonists or antagonists in the induction of oocyte maturation in fish.
Tokumoto
Toshinobu
T
Department of Biology and Geosciences, Faculty of Science, National University Corporation Shizuoka University, Shizuoka 422-8529, Japan. sbttoku@ipc.shizuoka.ac.jp
Tokumoto
Mika
M
Nagahama
Yoshitaka
Y
D000818:Animals; D004054:Diethylstilbestrol / Q000737:chemistry / Q000494:pharmacology; D052244:Endocrine Disruptors / Q000737:chemistry / Q000494:pharmacology*; D005260:Female; D009865:Oocytes / Q000166:cytology / Q000187:drug effects* / Q000254:growth & development; D010416:Pentachlorophenol / Q000737:chemistry / Q000494:pharmacology; D011987:Receptors, Steroid / Q000378:metabolism; D013256:Steroids / Q000737:chemistry / Q000494:pharmacology; D013629:Tamoxifen / Q000737:chemistry / Q000494:pharmacology; D015027:Zebrafish / Q000502:physiology*
D052244:Endocrine Disruptors; D011987:Receptors, Steroid; D013256:Steroids; C109512:maturation-inducing steroid receptor; D013629:Tamoxifen; D004054:Diethylstilbestrol; D010416:Pentachlorophenol