Cadmium exposure affects the expression of genes involved in skeletogenesis and stress response in gilthead sea bream larvae

Gilthead sea bream larvae (Sparus aurata) aged 47 days post hatching (dph) (11.6-12.8 mg in wet weight) were exposed to several sublethal concentrations of Cd2+ (0.1, 5 and 10 mg/L) during 6 days in order to investigate the effects of this heavy metal on the expression of selected genes involved in detoxification (metallothionein-mt, glutathione peroxidase 1-gpx1), stress response (heat shock protein 70-hsp70, tumour necrosis factor alpha-tnf alpha) and ossification (osteocalcin-oc) processes. For this purpose, specimens of 47 dph were exposed first for 72 h from 0.1 to 20 mg/L of Cd2+ in order to evaluate the median lethal concentration (LC50) for this metal, which was determined at 15.32 mg/L. Considering the results regarding the relative transcript levels of gpx1 and hsp70, Cd2+ at any of the tested levels (0.1, 5 and 10 mg/L) did not induce oxidative stress in gilthead sea bream larvae, whereas relative transcript levels of mt were increased at 5 and 10 mg/L of Cd2+ probably to detoxify this metal excess. Relative transcript levels of tnf alpha were not level dependent and were down-regulated in larvae exposed to 5 and 10 mg/L of Cd2+. At those concentrations, transcript levels of oc were down-regulated suggesting a disruption in bone mineralization. Results from this study provided insights in some molecular mechanisms underlying Cd2+-induced toxicity in fish at early stages of development. This is the first study to show that cadmium contamination can depress oc expression in teleosts.