Transcriptomic and Network Analyses Reveals Mechanistic-Based Biomarkers of Endocrine Disruption in the Marine Mussel, Mytilus edulis

Coastal monitoring in the 21st century faces challenges as measuring exposure using traditional toxicity approaches is not practical or financially feasible for the numerous contaminants entering oceans. Transcriptomics, high-throughput assays, and adverse outcome pathways (AOP) have been one approach to overcome these obstacles but development of these methods is challenging for non-model organisms and contaminants with unknown mechanisms. Endocrine Disrupting Compounds (EDCs) have been found to cause reproductive impairments such as intersex in bivalves, however, the mechanism linked to this adverse outcome (AO) is unknown as the estrogen receptor (ER) has been identified to be unresponsive to EDCs. To develop mechanism-based biomarkers that may be linked through an AOP we exposed Mytilus edulis to 17-alpha-ethinylestradiol (5 and 50ng/L) and 4-nonylphenol (1 and 100μg/L), and performed gene expression analysis on digestive gland tissue using a M. edulis microarray. Through network and targeted analyses, we identified the non-genomic estrogen signaling pathway and steroidogenesis pathway as the likely mechanism of action and identified biomarkers and potential key events (KE) for an AOP of endocrine disruption in marine mussels. The mechanism-based biomarkers were validated in the laboratory, tested in the field, and were responsive in areas known to be contaminated with EDCs. 40 samples total were analyzed. 4 replicates were examined for males and female Mytilus edulis in control, 5 and 50ng/L 17-alpha-ethinylestradiol (EE2) and 1 and 100μg/L 4-nonylphenol (4NP). Each male and female replicate came from separate experimental tanks.