Abstract
BackgroundAnimals 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 have not been well investigated in most invertebrates. Here, we performed genome survey for key defensome genes in Oikopleura dioica genome, and explored genome-wide gene expression using high density tiling arrays with over 2 million probes, in response to two model xenobiotic chemicals - the carcinogenic polycyclic aromatic hydrocarbon benzo[a]pyrene (BaP) the pharmaceutical compound Clofibrate (Clo).ResultsOikopleura genome surveys for key genes of the chemical defensome suggested a reduced repertoire. Not more than 23 cytochrome P450 (CYP) genes could be identified, and neither CYP1 family genes nor their transcriptional activator AhR was detected. These two genes were present in deuterostome ancestors. As in vertebrates, the genotoxic compound BaP induced xenobiotic biotransformation and oxidative stress responsive genes. 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.ConclusionsOikopleura has the smallest number of CYP genes among sequenced animal genomes and lacks the AhR signaling pathway. However it appears to have basic xenobiotic inducible biotransformation genes such as a conserved genotoxic stress response gene set. Our genome survey and expression study does not support a role of AhR signaling pathway in the chemical defense of metazoans prior to the emergence of vertebrates.
Highlights
Animals have developed extensive mechanisms of response to xenobiotic chemical attacks
Small cytochrome P450 (CYP) complement and no detectable CYP1-like gene BLAST Searches using CYP1 family protein sequences from various vertebrates and the invertebrates did not result in CYP- like sequences in O. dioica geneome
Phylogenetic analysis shows that none of the Oikopleura CYPs cluster with CYP1 family proteins from other organisms (Figure 1)
Summary
Animals have developed extensive mechanisms of response to xenobiotic chemical attacks. Recent genome surveys have suggested a broad conservation of the chemical defensome across metazoans, global gene expression responses to xenobiotics have not been well investigated in most invertebrates. We performed genome survey for key defensome genes in Oikopleura dioica genome, and explored genome-wide gene expression using high density tiling arrays with over 2 million probes, in response to two model xenobiotic chemicals - the carcinogenic polycyclic aromatic hydrocarbon benzo[a]pyrene (BaP) the pharmaceutical compound Clofibrate (Clo). Oikopleura dioica belongs to larvacean tunicates that have considerable importance in the marine ecosystem and for the vertical flux of carbon in the to explore the genome for selected defensome genes and initiate investigations of Oikopleura responses to chemical stressors, for comparisons with invertebrate and vertebrate model systems. AhR is a major xenobioticsensing receptor that is activated by environmental pollutants such as dioxin and PAHs including benzo[a]pyrene (BaP) [16,17]
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