Immediate and delayed effects of methylmercury exposure on behavior and gene expression of mangrove rivulus fish (Kryptolebias marmoratus)

Details

Supervisors

Valentine Chapelle ; Frédéric Silvestre

Faculty

Faculté des sciences

Degree label

Master [120] en biologie des organismes et écologie, à finalité approfondie

Abstract

Methylmercury (MeHg) is a pollutant recognized for its neurological effects impacting neuromotor activities. Early life stages are known to be sensitive to environmental stress and pollutant exposure, particularly during the central nervous system formation. In the present study, we aimed to highlight MeHg effects on neuromotor activities and its underlying mechanisms by focusing on immediate and delayed effects, as well as its impacts on related gene expression. To reach this goal, newly hatched larvae of the mangrove rivulus fish, Kryptolebias marmoratus, were exposed to two sub-lethal concentrations of MeHg (90 μg/L and 135 µg/L) for 7 days. This fish naturally produces isogenic lineages due to its self-fertilizing reproduction, which is unique among vertebrates. It thus provides genetic characteristics that allow to study how environment variation influence organism phenotype while minimizing genetic variability. In this study, behavioral tests were done on both 7 dph (days post-hatching) larvae and 90 dph adults to assess fish activity, foraging efficiency and thigmotaxis. A significant decrease was observed in larvae activity in both exposed groups. Furthermore, larvae exposed to 135µg/L of MeHg significantly expressed bolder behavior and tried to catch less prey than the control ones. On the opposite, none of those effects were observed for the adults in different exposition groups. Larvae whole bodies and adult brains of Kryptolebias marmoratus were also used for molecular analysis to determine the immediate and delayed effects of MeHg on gene expression using RTqPCR. For larvae we observed significant reduction of gene expression for NipBL, MeCP2, MAOA, DNMT3a and GSS in both exposed groups. On the opposite, no significant difference in gene expression was obtained between different exposure groups of adults. Our results confirm the impairment of larvae activity, thigmotaxis and foraging efficiency as well as the modification in gene expression by the MeHg exposure. We were not able to confirm those effects on adults. Further studies have to be done in order to evaluate the impact MeHg has on the epigenetic and how it could influence the behavior and genes expressions .