Effects of estrogenic compounds on biomarker gene expression in the brain of female Atlantic cod (Gadus morhua).

Dear reader, my name is Gwenaëlle Noally, I’m a graduate student in environmental toxicology and this blog post is the tale of my adventure as part of the dCod 1.0 project.


Spraying Fields


What is chemical pollution ?

“A growing peril” and “potential catastrophic risk” to humanity and wild life are the words used by numerous scientists to describe chemical pollution. Chemical pollution is the release of toxic compounds in the environment due to agricultural and industrial activities. Chemical pollution is considered a major threat to the ecosystems as it has been studied to be “poorly reversible”. The function and effect of those compounds on wildlife if therefore one of today’s and tomorrow’s biggest challenges.

Among environmental chemicals, estrogen mimicking endocrine disrupting chemicals (EDCs), also known as xenoestrogens, have the potential to disturb reproductive functions. In fish as in most vertebrates, estrogens play a key role in a range of physiological and reproductive processes. The pesticides Dichlorodiphényltrichloroéthane (DDT) and methoxychlor (MXC) as well as  the plasticizer bisphenol A (BPA) and the pharmaceutical estrogen ethynylestradiol (EE2) are among known estrogenic EDCs present in the environment.


The aim of our project was to investigated the effects of EDCs on the expression of the target genes involved in reproductive processes in the brain of juvenile female Atlantic cod (Gadus morhua).

To do so, we exposed female Atlantic cod to three EDCs (MXC, BPA and EE2) at different concentrations and collected brain samples after three days of treatment. We then extracted RNA from the brain samples. The expression levels of the biomarker genes was determined using a quantitative polymerase chain reaction (qPCR). qPCR is a powerful technique that allows exponential amplification of DNA sequences in a sample. Statistical analysis was performed using a One -Way ANOVA test in R (Version 4.2.1). In total, five genes involved in the reproductive system of fish were analyzed.


Figure1: Quantification of the aromatase gene Cyp19a1b using real-time RT-PCR and LightCycler® 480 SYBR Green I Master mix technology. Cyp19a1b is involved in the estrogen synthesis. Excellent reproducibility is shown in the amplification curves.


Our observations demonstrate that endocrine disrupting chemicals were responsible for an upregulation of the biomarker genes in the brain of female Atlantic cod. This suggests the adverse effect of EDCs on reproductive functions of Atlantic Cod.  Moreover, variation in the target genes transcriptome may be responsible for a wild range of physical and metabolism changes in fish.  Karren A. Kidd study (Kidd 2007) showed a feminization of male fish in the exposed to EE2 at the Experimental Lakes Area (ELA) in northwestern Ontario, Canada.  Due to municipal wastewaters containing estrogen mimics, the sustainability of  those wild fish populations observed in Canadian freshwaters could be severely impacted. (Kidd 2007).

Impact on human reproductive system ?

EDCs became so prevalent in the environment that we can imagine being exposed to them on a regular basis, directly or indirectly. Yet, the sexual hormone estrogens is similar to all vertebrates which pushes us to think that those compounds could also impact our reproductive system. Several research associate exposure to endocrine disrupting chemicals (EDCs) with major human diseases. Though, due to the complexity of the method, no significant relationship between the disorders and the chemicals is yet to be found.


I wish to thank my supervisor, Fekadu Yadetie, for introducing me to not only methods, but also the excitement of findings assessment. I would also like to express my gratitude to every person involved in this project as well as the whole Toxicology research group at UiB for making me feel welcome.


Thank you for reading,


Gwenaëlle Noally

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