Metal distribution and metallothionein induction after cadmium exposure in the terrestrial snail Helix aspersa (Gastropoda, Pulmonata)

Abstract

The aim of the present work was to study the effect of Cd2+ exposure on metallothionein (MT) induction and on the distribution of metals (Cd, Cu, and Zn) in the terrestrial pulmonate Helix aspersa. In particular, the soluble and nonsoluble pools of the accumulated metals and their tissue distribution in uncontaminated and contaminated edible snails were investigated after a two-week exposure to Cd2+. In the soluble cytosolic pool of the midgut gland of H. aspersa, three metal-specific putative MT isoforms were separated following a fractionation protocol with diethylaminoethyl cellulose, size-exclusion chromatography, ultrafiltration, and reversed-phase high-performance liquid chromatography (RP-HPLC). Interestingly, one of the above isoforms seems to bind both Cd and Cu, which may in addition mobilize, after induction by Cd2+, some of the intracellular Cu and, thus, perhaps increase the Cu pool in the cytosolic fraction. The cDNA and its translated amino acid sequence of a Cd2+-binding MT isoform from the snail midgut gland was characterized and attributed to one of the putative MT isoforms obtained by RP-HPLC. The amino acid sequence of this Cd-MT isoform of H. aspersa differed from similar sequences described in other terrestrial pulmonates, such as Helix pomatia or Arianta arbustorum, by only a few amino acids (n = 4 and 8, respectively). That the identified Cd-MT from H. aspersa is inducible by Cd2+ also was shown, chromatographic evidence aside, by a specific polymerase chain reaction protocol on a cDNA basis, which included a noninducible housekeeping gene as a control.

Physiological relevance and contribution to metal balance of specific and non-specific Metallothionein isoforms in the garden snail, Cantareus aspersus

“…4c, d; Table 2). The nearly exclusive Cu content of this isoform, and its independence of the state of Cd accumulation in the snail, corroborates the view that CaCuMT may be involved in the homeostatic regulation of Cu, rather than being responsible for detoxification processes (Dallinger et al 2005;Hispard et al 2008). This is in concordance with the observation that the transcription of CaCuMT in the midgut gland of C. aspersus does not vary as a function of supra-physiological exposure to Cd or Cu.…”

“…1a), previously isolated and characterised from the midgut gland of H. pomatia (Dallinger et al 1993Berger et al 1997). The third MT isoform (CaCd/ CuMT), first identified in C. aspersus among all snail species Hispard et al 2008), exhibits a sequence with intermediate peculiarities between those of CaCuMT and CaCdMT (Fig. 1a) and is largely similar to the corresponding isoform in H. pomatia which occurs in two allelic variants (Fig.…”

“…During this time, metal accumulation and transcriptional activation of the three MT isoforms were assessed in the snail midgut gland, since this organ accounts for most of the short and long-term metal accumulation in pulmonate snails (Dallinger and Wieser 1984;Hispard et al 2008).…”

“…4d). In fact, due to this mixed metal-binding character, this isoform had been designated as CaCd/CuMT Hispard et al 2008). The quantitative analysis of its metal content showed that Cd and Cu were present at a molar ratio of about [1 Cu:0.5 Cd], with only traces of Zn (Table 2).…”

Effects of Date Palm (Phoenix dactylifera) Seed Extract on Heavy Metals Concentrations in Carp (Cyprinus carpio)

“…The metal binding domain of MTs consists of 20 cysteine residues juxtaposed with basic amino acids (lysine and arginine) arranged in two thiol-rich sites [34]. Based on their affi nity to metals these proteins are able to transport essential metals to a place of need or detoxify toxic metals to protect cells [35]. Two isoforms of MT, MT-1 and MT-2, are described in all vertebrates, including fi sh [36].…”