Characterization of proxiredoxins’ coding genes in Ciona intestinalis.

Ascidians represent an interesting model from an evolutionary and ecotoxicology point of view, because of their large distribution in temperate sea and their phylogenetic position of invertebrate chordates. Immune responses imply an increase in oxygen consumption with a consequent risk of oxidative stress. With the aim to study the components of the antioxidant defense system in the solitary ascidian Ciona intestinalis, we characterized gene sequences encoding peroxiredoxins (Prxs), non-selenium peroxidases that are able to reduce hydrogen peroxide, organic hydroperoxides and peroxynitrite. Thus they represent a class of important antioxidant enzymes, that protect cells against oxidative stress. In the GeneBank database five Prx sequences are present, Prx2, 3, 4, 6a and 6b. The multi-alignment analysis, conducted with orthologous sequences of vertebrates and invertebrates, showed that in Ciona’s Prxs the amino acids essential for their enzymatic activity are highly conserved, namely the catalytic tetrad consisting of proline, threonine, cysteine and arginine. Preliminary phylogenetic reconstruction indicates that Prx3 and 4 emerge as sister group of Prxs of the respective vertebrates groups (or isoforms), while Prx2, 6a and 6b have an uncertain position. A partial confirmation of phylogenetic results was obtained with the analysis of homology modeling, according to which Prx3 and 4 present a structure similar to that of two vertebrate proteins, Bos taurus Prx3 and Larimichthys crocea Prx4, respectively, while Prx2 and 6 six have a three dimensional structure similar to that of two invertebrate proteins, Ancylostoma ceylanicum Prx1 and Arenicola marina Prx6, respectively. The transcription of all these genes, measured by qRT-PCR, resulted variable in different organs (intestine, ovary, pharynx, stomach). In particular, the ovary is the organ that expresses the highest level of messenger for all Prxs. Preliminary data were also collected about the possible circadian expression of Prx.