Early and late response of Nematostella vectensis transcriptome to heavy metals

Environmental contamination from heavy metals poses a global concern for the marine environment, as heavy metals are passed up the food chain and persist in the environment long after the pollution source is contained. Cnidarians, dating back to 700 million years ago, play an important role in shaping marine ecosystems, but environmental pollution profoundly affects their vitality. Among the cnidarians, the sea anemone Nematostella vectensis is an advantageous model for addressing questions in molecular ecology and toxicology as it tolerates extreme environments and its genome has been published. Here we employed a transcriptome-wide RNA-Seq approach to analyze N.vectensis molecular defense mechanisms against four heavy metals: Hg, Cu, Cd and Zn. Altogether, more than 5000 transcripts showed significant changes in gene expression, with Hg having the greatest impact on up-regulating transcripts, followed by Cu, Cd and Zn. We identified, for the first time, co-up-regulation of immediate-early transcription factors such as Egr1, AP1 and NF-κB. Time-course analysis of these genes revealed their early expression as rapidly as one hour after exposure to heavy metals, suggesting that they may complement or substitute for the roles of the metal mediating Mtf1 transcripton factor. We further characterized regulation of a large array of stress-response gene families including Hsp, ABC, CYP members and phytochelatin synthase that may regulate synthesis of the metal-binding phytochelatins instead of the methallothioneins that are absent from Cnidaria genome. This study provides mechanistic insight into heavy-metal toxicity in N.vectensis and sheds light on ancestral stress adaptations.