Microcystin-LR (MCLR) is the most toxic and most frequently encountered hepatotoxin in the aquatic environment. This study investigated the protein profiles of zebrafish (Danio rerio) livers chronically exposed to MCLR concentrations (2 or 20 μg/l) using the proteomic approach as well as cell ultrastructure, protein phosphatase (PP) activity, protein phosphatase 2A (PP2A) abundance, and toxin content analysis of the hepatic tissue. The results showed that, after 30-day exposure, the presence of MCLR strikingly enhanced toxin accumulation and the PP activity in zebrafish livers. However, the PP2A amounts were independent of toxin treatments. MCLR caused a noticeable damage to liver ultrastructure, a widespread swelling in the rough endoplasmatic reticulum and mitochondria was observed in the MCLR-exposed hepatocytes, and a honeycomb-like structure was formed in the treated nucleoli. Comparison of two-dimensional electrophoresis (2-DE) protein profiles of MCLR-exposed and nonexposed zebrafish livers revealed that the abundance of 22 proteins, measured by 2-DE, was remarkably altered in response to toxin exposure. These proteins were involved in cytoskeleton assembly, macromolecule metabolism, oxidative stress, and signal transduction, indicating that MCLR toxicity in fish liver is complex and diverse. Thus, proteomics provides a new insight into MCLR toxicity, that chronic toxicity of MCLR is different from acute toxicity, and we speculate that the reactive oxygen species pathway might be the main toxic pathway instead of the PP one. Moreover, even a low concentration of MCLR in water could significantly interrupt cellular processes, and more care should be taken in determining the criterion for MCLR content in drinking water.

The tropical green-lipped mussel Perna viridis is a common biomonitor throughout the Indo-Pacific region that is used for environmental monitoring and ecotoxicological investigations. However, there is limited molecular data available regarding this species. We sought to establish a global transcriptome database from the tissues of adductor muscle, gills and the hepatopancreas of P. viridis in an effort to advance our understanding of the molecular aspects involved during specific toxicity responses in this sentinel species. Illumina sequencing results yielded 544,272,542 high-quality filtered reads. After de novo assembly using Trinity, 233,257 contigs were generated with an average length of 1,264 bp and an N50 length of 2,868 bp; 192,879 assembled transcripts and 150,111 assembled unigenes were obtained after clustering. A total of 93,668 assembled transcripts (66,692 assembled genes) with putative functions for protein domains were predicted based on InterProScan analysis. Based on similarity searches, 44,713 assembled transcripts and 25,319 assembled unigenes were annotated with at least one BLAST hit. A total of 21,262 assembled transcripts (11,947 assembled genes) were annotated with at least one well-defined Gene Ontology (GO) and 5,131 assembled transcripts (3,181 assembled unigenes) were assigned to 329 Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways. The quantity of assembled unigenes and transcripts obtained from male and female mussels were similar but varied among the three studied tissues, with the highest numbers recorded in the gills, followed by the hepatopancreas, and then the adductor muscle. Multivariate analyses revealed strong tissue-specific patterns among the three different tissues, but not between sexes in terms of expression profiles for annotated genes in various GO terms, and genes associated with stress responses and degradation of xenobiotics. The expression profiles of certain selected genes in each tissue type were further validated using real-time quantitative polymerase chain reaction assays and a similar tissue-specific trend was seen. The extensive sequence data generated from this study will provide a valuable molecular resource for facilitating environmental studies with P. viridis, and highlight the importance of tissue-specific approaches in the future.