Effect of Polycyclic Aromatic Hydrocarbons on Development of the Ascidian

Polycyclic aromatic hydrocarbons (PAHs) are pollutants that exert harmful effects on marine invertebrates; however, the molecular mechanism underlying PAH action remains unclear. We investigated the effect of PAHs on the ascidian Ciona intestinalis type A (Ciona robusta). First, the influence of PAHs on early Ciona development was evaluated. PAHs such as dibenzothiophene, fluorene, and phenanthrene resulted in formation of abnormal larvae. PAH treatment of swimming larva induced malformation in the form of tail regression. Additionally, we observed the Ciona aryl hydrocarbon receptor (Ci-AhR) mRNA expression in swimming larva, mid body axis rotation, and early juvenile stages. The time correlation between PAH action and AhR mRNA expression suggested that Ci-AhR could be associated with PAH metabolism. Lastly, we analyzed Ci-AhR mRNA localization in Ciona juveniles. Ci-AhR mRNA was localized in the digestive tract, dorsal tubercle, ganglion, and papillae of the branchial sac, suggesting that Ci-AhR is a candidate for an environmental pollutant sensor and performs a neural function. Our results provide basic knowledge on the biological function of Ci-AhR and PAH activity in marine invertebrates.