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Fish are commonly exposed to environmental pollutants, which in turns could induce an oxidative stress. So, it is important to understand the effects and the responses elicited by these toxicants in fish species, being fish cell lines important tools for this purpose. Thus, the aim of the present study was to compare the effects of copper and UV-B radiation exposure on zebrafish hepatocytes (ZFL lineage) in terms of reactive oxygen species (ROS) levels, sulfhydril groups content and mRNA levels of important genes related to cellular response to toxic agents. Exposure of ZFL cells to UV-B radiation (23.3 mJ/cm(2)) significantly increased levels of intracellular ROS and mRNA of both superoxide dismutase isoforms (sod1 and sod2), three glutathione S-transferase isoforms (gstα, gstµ and gstπ) and a heat shock protein (hsp70). However, no changes in nonprotein sulfhydryl groups (NP-SH) content, as well as in the mRNA levels of genes related to glutathione (GSH) synthesis and recycling, were observed. Contrary to this, copper exposure (20 mg/L) diminished NP-SH content and increased the levels of mRNA of genes related to GSH synthesis (gclc and gs). Moreover, copper exposure increases the mRNA levels of some genes related to antioxidant defenses (gpx and gstπ), biotransformation reactions (cyp1a1) and protein repair (hsp70). In conclusion, these results demonstrated that both toxicants could increase ROS levels in ZFL cell line, but the responses are different, which could be related to activation of different signaling pathways.

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The major role of the p53 gene family is related to the maintenance of genetic stability, protecting organisms from a wide range of stressors. Considering the importance of p53 in cancer development, this study aimed to analyze the expression of p53 isoforms in the mussel Mytilus edulis after lead exposure. We detected the p53 isoform both in the gills and in the digestive gland of mussels, but detected TAp63/73 and ∆Np63/73 isoforms only in the gills. Lead exposure induced upregulation of p53 mRNA levels in the digestive gland, without any effect in the gills. Conversely, mRNA levels of the TAp63/73 and ∆Np63/73 isoforms were downregulated in the gills after 1 d of exposure to lead. These results suggest that some similarities may exist between vertebrates and invertebrates and, specifically, that the balance between isoforms may represent a crucial step in cellular homeostasis. Moreover, the transcription of these cancer‐related genes seems to be regulated in a tissue‐ and time‐specific manner.