Effects of heavy metals on the expression of a zinc-inducible metallothionein-III gene and antioxidant enzyme activities in Crassostrea gigas

Abstract

Sequestration by metallothioneins and antioxidant defense are two kinds of important defense mechanisms employed by mollusks to minimize adverse effects caused by heavy metal contaminants in marine environment. In the present study, a novel metallothionein gene, CgMT-III, was cloned from Crassostrea gigas, consisting of eighteen conserved cysteine residues and encoding a MT III-like protein with two tandem b domains. The expression level of CgMT-III transcript induced by zinc was much higher than that induced by cadmium exposure. It suggested that CgMT-III was perhaps mainly involved in homeostatic control of zinc metabolism, which was distinct from previously identified MTs in C. gigas. Among the tested antioxidant enzymes including superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), SOD and GPx showed varying up-regulations in a tissuespecific manner, while CAT activities were inhibited in both gill and hepatopancreas from C. gigas exposed to heavy metals. It can be inferred that CgMT-III was mainly involved in zinc homeostasis, and CgMT-III gene together with CAT enzyme could be potential biomarkers to indicate heavy metal, especially zinc pollution in marine organisms.

A Novel Metallothionein Gene from Mussel, Hyriopsis cumingii: Identification and Expression under Lanthanum Exposure

“…In mollusks, several MTFs and MREs were identified; for example, three MREs were found in CvMT‐I/II and CvMT‐IV (Jenny et al ), and two MTFs in oyster, Crassostrea gigas (Qiu et al ). These studies together with other reports revealed the diversity of metal inducibility and expression pattern in different mollusk MT isoforms (Amiard et al ; Jenny et al ; Cong et al ). To further understand the multiplicity of mollusk MT function and its regulating mechanisms, more gene sequence data are required.…”

“…Metallothionein (MT) is a low‐molecular‐weight, metal‐binding, and cysteine‐rich protein first isolated in renal cortical cells of Equus caballus (Margoshes and Vallee ). Since then, MT was identified in many organisms including aquatic invertebrate mollusks (Binz and Kägi ; Amiard et al ; Cong et al ). Based on structural relationships, MTs have been subdivided into three classes (Fowler et al ).…”

Diversification and domain evolution of molluskan metallothioneins: a mini review

“…The arrangement pattern of nine Cys is obviously similar with the β 2 -domain of the gastropod β 1 β 2 -MTs (Jenny et al 2006;Jenny et al 2016). The same β 2 β 2 -domain structure has also been found in C. gigas MT-III (JF781299); however unlikely in C. virginica, multiple MT-III subisoforms have not been characterized in C. gigas (Cong et al 2012). The C. gigas MT-III shows a series of substitutions of non-Cys aa from the C. virginica MT-III isoforms.…”

“…Further, C. virginica MT-III represented only a moderate responsiveness to heavy metal exposures in both larvae and adults (Jenny et al 2006). However, on the contrary, the C. gigas MT-III has been reported to be significantly induced by zinc (as a main regulator for zinc homeostasis), and it may be a participating member for cadmium detoxification in the adult tissues (Cong et al 2012). Thereby, it suggests the functional differentiation/divergence of MT-III isoforms during speciation events in the Crassostrea lineage.…”

Metallothionein 1 family profiling identifies MT1X as a tumor suppressor involved in the progression and metastastatic capacity of hepatocellular carcinoma

“…MT1s are involved in diverse functions, such as metal homeostasis, metal donation to different enzymes, angiogenesis, apoptosis, cell differentiation, radiation cell damage as well as carcinogenesis . Given their broad regulatory properties, MT1s have also been suggested to play important roles in cell senescence and various pathological processes, such as neurodegeneration, osteoarthritis, metabolic disorders, and certain immune processes . In recent years, some postulated pathophysiological effects of MT1s have been associated with distinct functional polymorphisms of MT1 genes …”