Genome-wide transcriptional responses to benzo[a]pyrene and clofibrate in the tunicate Oikopleura dioica

Animals have developed extensive mechanisms of response to xenobiotic chemical attacks. Although recent genome surveys have suggested a broad conservation of the chemical defensome across metazoans, global gene expression responses to xenobiotics are not known in most invertebrates. Here, using high density tiling arrays with over 2 million probes, we explored genome-wide gene expression in the tunicate Oikopleura dioica in response to two model xenobiotic chemicals – the carcinogenic polycyclic aromatic hydrocarbon benzo[a]pyrene (BaP) the pharmaceutical compound Clofibrate (Clo). The genotoxic compound BaP induced xenobiotic biotransformation and oxidative stress responsive genes, as in vertebrates. Notable exceptions were genes of the aryl hydrocarbon receptor (AhR) signaling pathway. Clo also affected the expression of many biotransformation genes and markedly repressed genes involved in energy metabolism and muscle contraction pathways. Oikopleura appears to have basic defensome toolkit consisting of phase I, phase II and phase III biotransformation genes. Exposure of about 130 four-days-old animals in 1L seawater in glass beakers. Pooled animals used, no replicates. DMSO Treatments: -Clofibrate (Clo) (Sigma-Aldrich, St. Louis, MO): 1 µM and 5 µM. -Benzo[a]pyrene (BaP (Sigma-Aldrich): 0.2 µM and 1 µM - Controls received 1 ml Dimethyl sulfoxide (DMSO). -The animals kept at room temperature and harvested after 10 hrs and frozen. -Total RNA was isolated from the pooled animals using the RNeasy Mini Kit according to manufacturer’s protocols (QIAGEN, Hilden, Germany). - 5 µg total RNA was converted to dscDNA using SuperScript Double-Stranded cDNA Synthesis Kit (Invitrogen, Carlsbad, CA), and dscDNA samples were submitted for microarray analysis. BaP and Clo treated samples were labeled using Cy3-coupled random nonamers and DMSO controls were labeled using Cy5-coupled random nonamers. Total 4 hybridizations for the 8 samples (single hybridization for each treatment and DMSO control pair), no replicates.