Contents lists available at ScienceDirect Comparative Biochemistry and Physiology, Part C journal homepage: www.elsevier.com/locate/cbpc Molecular characterization and metal induced gene expression of the novel glutathione peroxidase 7 from the chordate invertebrate Ciona robusta Ferro D. a , Franchi N. b , Bakiu R. c , Ballarin L. b, ⁎ , Santovito G. b a Institute for Evolution and Biodiversity, Westfälische Wilhelms-Universität, Münster, Germany b Department of Biology, University of Padova, Padova, Italy c Department of Aquaculture and Fisheries, Agricultural University of Tirana, Tirana, Albania ARTICLE INFO Keywords: Antioxidant system Reactive oxygen species Metals Chordate invertebrate Ciona robusta Glutathione peroxidase ABSTRACT In the present study, we describe the identified and characterized the gene and the transcript of a novel glu- tathione peroxidase-7 (GPx7) from the solitary ascidian Ciona robusta, an invertebrate chordate widely dis- tributed in temperate shallow seawater. The putative nucleotide and amino acid sequences were compared with those of GPx7 from other metazoans and phylogenetic analysis suggests the presence of a high evolutionary pressure in the contest of neutral evolution. The mRNA of CrGPx7 is located in hemocytes and ovarian follicular cells, as revealed by in situ hybridization. The time course of CrGPx7 mRNA levels in the presence of Cd, Cu and Zn, showed upregulation in the final stages of the experiments, suggesting a role of GPx7 in late protection from oxidative stress. Our in silico analyses of the crgpx7 promoter region revealed putative consensus sequences similar to mammalian metal-responsive elements (MRE) and xenobiotic-responsive elements (XRE), suggesting that the transcription of these genes directly depends on metals. Cell-free extract from C. robusta tissues show the presence of selenium-independent GPx activity that is inhibited by the presence of metals. 1. Introduction The antioxidant system is one of the most important metabolic pathways of eukaryotic cells as the production of reactive oxygen species (ROS) is a shared feature of all aerobic organisms. In the mi- tochondria, indeed, electrons moving through the electronic transport chain reach the available oxygen and generate ROS (Halliwell and Gutteridge, 1984). ROS are produced also in other metabolic, immune, and toxicological processes such as aging, host-parasite interactions and xenobiotic exposure (Blagosklonny, 2008; Günther et al., 2012; Kohchi et al., 2009). However, ROS have negative effects on cell physiology promoting redox state unbalance that results in the oxidation of bio- molecules, leading, for instance, to membrane lipid or nucleic acid peroxidation, with deleterious consequences for cell vitality (He and Zuo, 2015). Syndromes such as Alzheimer's disease, Parkinson's disease and diabetes are only few examples from a long list of ROS-dependent human diseases (Brieger et al., 2012; Dumont and Beal, 2011; Fransen et al., 2012; Valko et al., 2007) and this confirms the importance of an effective antioxidant defense system. In order to prevent ROS-related tissue/organ damages, organisms set up a series of antioxidant systems based on the reducing activity of enzymes or thiol-rich molecules. Antioxidant enzymes such as superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), methionine sulfoxide reductase (Msr) and peroxiredoxin (Prdx), have a pivotal role in this homeostatic and detoxification system. These molecular components of the cell have been conserved throughout deep evolutionary time in all eukaryotic organisms, from yeast to vertebrates (Boldrin et al., 2008; Irato et al., 2007; Ricci et al., 2017; Santovito et al., 2002; Tolomeo et al., 2016). Oceans and seas harbor the great majority of animal biodiversity. However, despite the abundance of data on the antioxidant systems of marine vertebrates (Santovito et al., 2006; Sattin et al., 2015; Tolomeo et al., 2016), data for marine invertebrates are still limited and scat- tered (Bakiu and Santovito, 2015; Irato et al., 2003, 2007; Santovito et al., 2015, 2005). Members of the subphylum Urochordata are marine, filter-feeding organisms closely related to vertebrates (Delsuc et al., 2006). Given their peculiar phylogenetic position, elucidating the antioxidant sys- tems of these animals can be extremely interesting from an evolutionary point of view. C. robusta is a widely used model organism for com- parative and evolutionary studies. In our previous papers (Franchi et al., 2011, 2012, 2014; Ferro et al., 2013), it was called Ciona in- testinalis. However, what formerly known as C. intestinalis was recently recognized as two different species: C. intestinalis and C. robusta (Brunetti et al., 2015; Pennati et al., 2015). It results that our model https://doi.org/10.1016/j.cbpc.2017.12.002 Received 25 September 2017; Received in revised form 8 December 2017; Accepted 12 December 2017 ⁎ Corresponding author. E-mail address: loriano.ballarin@unipd.it (L. Ballarin). Comparative Biochemistry and Physiology, Part C 205 (2018) 1–7 Available online 16 December 2017 1532-0456/ © 2017 Elsevier Inc. All rights reserved. T