Effects of okadaic acid and phytoplankton ingestion on nr1j1, cyp, and abcb1 gene expression in Mytilus galloprovincialis

Four nr1j1 gene sequences were recently reported in the marine mussel Mytilus galloprovincialis. These genes are orthologs of the nuclear receptor family NR1I found in vertebrates, whose members like the pregnane x receptor (PXR) are known to play a major role in the regulation of xenobiotic metabolism. Building on recent evidence that these four genes encode functional proteins, this study aims to deepen our understanding of nr1j1 genes by analyzing their expression in adult mussels exposed to different diets consisting of microalgae and cyanobacteria, and to the biotoxin okadaic acid. In parallel, we analyzed the expression of several nr1j1 putative target genes, such as cyp3-like and abcb1. Our results showed that gene expression regulation may be organ-specific and time-dependent, and that diet and food intake can affect the expression of the genes studied. The highest nr1j1 and cyp3-like transcriptional activation was observed in mussels fed with Tetraselmis sp., while abcb1 genes showed higher expression in mussels fed with toxic cyanobacteria. In contrast, exposure to okadaic acid did not induce changes in the expression of the analyzed genes. This work demonstrates that xenobiotic metabolism responses in mussels can be modulated by diet and exposure to biotoxins, underscoring the importance of diet in the elimination of toxic substances in mussels. The exact mechanisms underlying the observed transcriptional activation of the nr1j1 genes remain unknown.