Early and late response of Nematostella vectensis transcriptome to heavy metals

Abstract

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 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 analyse N. vectensis molecular defence mechanisms against four heavy metals: Hg, Cu, Cd and Zn. Altogether, more than 4800 transcripts showed significant changes in gene expression. Hg had the greatest impact on up-regulating transcripts, followed by Cu, Zn and Cd. We identified, for the first time in Cnidaria, 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 transcription factor. We further characterized the 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 metallothioneins 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.

Regulation of AP-1 by MAPK Signaling in Metal-Stressed Sea Anemone

“…In Cnidaria, AP-1 was suggested to mediate stress responses such as upon elevation in seawater temperature and injury as well as exposure to heavy metals, which we previously showed to affect fos transcript [25, 26, 28, 54]. Here, we show the involvement of MAPKs in the regulation of AP-1 transcripts fos1 and jun1 in the presence of Hg.…”

“…RNA was extracted from Hg-treated and untreated anemones using Tri-reagent (Sigma-Aldrich) and purified as described previously [25]. qPCR was performed using the StepOnePlus Real-Time PCR System (Applied Biosystems) and β-actin was used as an internal control as described previously [25].…”

“…qPCR was performed using the StepOnePlus Real-Time PCR System (Applied Biosystems) and β-actin was used as an internal control as described previously [25]. For primers and GenBank accession numbers, (for all online suppl.…”

“…Nematostella tolerates a wide range of anthropogenic and environmental changes and, in recent years, it has become a valuable cnidarian model for molecular ecology and stress regulation studies [21-24]. To understand the molecular pathway by which the metal signal is transduced and induced oxidation stress in Cnidaria, we recently conducted a detailed transcriptomic analysis in Nematostella upon exposure to four metals [25]. Among our findings, we have identified rapid activation of several immediate-early response genes such as the transcription factors early growth response1 ( egr1 ) and fos .…”

Current directions and future perspectives from the third Nematostella research conference

“…Ron Elran and Maayan Raam (Lotan laboratory, University of Haifa, Israel) presented a study of the transcriptomic responses of Nematostella following exposure to mercury, cadmium, copper and zinc (Elran et al, 2014). Broadly, they found that only a few genes were differentially expressed in response to all four metals and that copper- and mercury-treated anemones exhibited expression patterns that were relatively similar to one another.…”