Ovarian gene transcription and effect of cadmium pre-exposure during artificial sexual maturation of the European eel (Anguilla anguilla)

Abstract

European eels are dangerously threatened with extinction. Recent advances tend to show that pollution could, in addition to other already identified factors, contribute to this drama. In a previous report, cadmium (Cd) pre-exposure was found to strongly stimulate the pituitary-liver-gonad axis of maturing female silver eels, leading, lastly, to oocytes atresia and eels mortality. The present work was performed to get more insights into the effects of Cd preexposure on eels' ovaries. The transcription levels of various genes involved in mitochondrial metabolism, in the cellular response to metal (metallothioneins, MTs) and oxidative stress (catalase, CAT) were investigated. Our results show that ovarian growth is associated with an up-regulation of mitochondrial genes. However, Cd pre-exposure was found to significantly impair this up-regulation. Such findings could explain, at least in part, why oocytes of Cd pre-contaminated eels could not reach final maturation. Concerning MTs, despite the end of the experiment was marked by a strong increase in their gene transcription levels in both eel groups, MTs protein content was found to increase only in the case of Cd pre-contaminated eels. Since this increase in MTs protein content was associated with a massive entry of Cd in gonads, our findings suggest that MTs mRNA, that are normally accumulated in oocytes to cope with the future needs, can be activated and translated in response to Cd exposure.