The chemical defensome of fish

Interspecies differences in sensitivity to chemical exposures pose a great challenge in toxicological risk assessments. How an organism copes with chemicals is largely determined by the genes and proteins that collectively function to defend against, detoxify and eliminate chemical stressors. This integrative network includes receptors and transcription factors, biotransformation enzymes, transporters, antioxidants, and metal- and heat-responsive genes, and is collectively known as the chemical defensome. Although the types of defensome genes are generally conserved in animals, there are important differences in the complement and function of specific genes between species. Being the largest group of vertebrate species, teleost fish can provide valuable insight into the evolution and functional diversity of defensome genes.

In this study, we compared the genes comprising the chemical defensome of five fish species that span the teleosteii evolutionary branch and are often used as model species in toxicological studies and environmental monitoring programs, including Zebrafish (Danio rerio), Atlantic cod (Gadus morhua), medaka (Oryzias latipes), Atlantic killifish (Fundulus heteroclitus) and stickleback (Gasterosteus aculeatus). Genome mining revealed evolved differences in the number and composition of defensome genes that can have implication for how the species sense and respond to environmental pollutants. Furthermore, we show that there are important differences in expression of chemical defense genes between stickleback and zebrafish during early development. The results indicate that the diversity and function of the defensome will be important for toxicological testing and risk assessments studies.