Changes in Embryonic Zebrafish Cardiac Gene Expression Following Crude Oil Exposure

Crude oil and its degradation byproducts are known to have cardiotoxic effects on early life-stage fish including commercial species such as tuna and salmon. Exposed fish often exhibit pericardial edema and impaired heart function at very low exposure concentrations. This study examined the timed induction of several genes in response to crude oil exposure, including cytochrome P450 (cyp1a) and bone morphogenic protein 10 (bmp10) in embryonic zebrafish (Danio rerio), a model organism. Cyp1a is a widely studied gene involved in the metabolism of xenobiotic (foreign) substances. Bmp10 is a cardiac gene involved in Ca²⁺ signaling, and is a likely contributor to oil-induced cardiac abnormalities. However, the timing of cardiac gene induction after crude oil exposure is unknown in both zebrafish and commercially important fish species. In this study, zebrafish were continuously exposed to a crude oil water-associated fraction (WAF) starting at 24 hours post fertilization (hpf) with four replicates per treatment including water-only controls. Twenty embryos were sampled per replicate at seven timepoints between 24hpf and 48hpf. RNA was extracted from each sample and converted to cDNA. Using a comparative Ct method, expression changes in genes of interest were measured using real time quantitative polymerase chain reaction (rt-qPCR), and analyzed using various statistical tests in R. Statistically significant upregulation of calcium signaling genes support a decrease in fitness of early life-stage zebrafish after exposure to low concentrations of crude oil. Likewise, this study has direct implications to the health and viability of commercially important fish exposed to oil spills in marine environments.