The Paracentrotus lividus metallothionein gene family: structure and expression.

Metallothioneins are metal binding proteins that play a pivotal role in metal homeostasis and detoxification. Since their initial discovery, they have been extensively studied in a variety of organisms ranging from microbes to plants and animals. Organisms often possess multiple genes encoding metallothionein homologs with distinct properties, such as varying affinities for different metals, and in many cases different functions. Despite the plethora of available studies, very little information is known about sea urchin P. lividus MT (1, 2). We previously identified five Pl-MT embryonic cDNAs and we studied their induction after cadmium treatment (3). Now we studied their expression during embryo development by RT-qPCR. MT4 to MT6 are not expressed during normal development (very low levels of MT5 at pluteus stage), while MT7 mRNA level strikingly increases throughout embryonic development and MT8 rises until gastrula stage and decreases thereafter. Preliminary in situ hybridization experiment results indicate that both MT7 and MT8 are expressed in the archenteron at pluteus stage, but MT7 is expressed also in the oral ectoderm. We also isolated and sequenced the corresponding MT genes: all the Pl-MT genes have a similar structure (4 exons separated by 3 introns, the last intron into the 3'UTR) having introns in the same positions as S. purpuratus genes, but they are different from other deuterostomes. MT promoters were analyzed in silico: putative metal response elements (MRE), antioxidant response elements (ARE) were identified, but their copy number and positions are different between constitutive (MT7-8) and induced (MT4-5-6) genes. 1 Russo, R, et al. (2003) Cell Stress Chaperones, 8, 232-41 2 Russo, R, et al. (2013) Gene, 519, 305-10 3 Ragusa, MA, et al. (2013) Mol Biol Rep, 40, 2157-67