Abstract
Terrestrial snails (Gastropoda) possess Cd-selective metallothioneins (CdMTs) that inactivate Cd2+ with high affinity. Most of these MTs are small Cysteine-rich proteins that bind 6 Cd2+ equivalents within two distinct metal-binding domains, with a binding stoichiometry of 3 Cd2+ ions per domain. Recently, unusually large, so-called multi-domain MTs (md-MTs) were discovered in the terrestrial door snail Alinda biplicata (A.b.). The aim of this study is to evaluate the ability of A.b. to cope with Cd stress and the potential involvement of md-MTs in its detoxification. Snails were exposed to increasing Cd concentrations, and Cd-tissue concentrations were quantified. The gene structure of two md-MTs (9md-MT and 10md-MT) was characterized, and the impact of Cd exposure on MT gene transcription was quantified via qRT PCR. A.b. efficiently accumulates Cd at moderately elevated concentrations in the feed, but avoids food uptake at excessively high Cd levels. The structure and expression of the long md-MT genes of A.b. were characterized. Although both genes are intronless, they are still transcribed, being significantly upregulated upon Cd exposure. Overall, our results contribute new knowledge regarding the metal handling of Alinda biplicata in particular, and the potential role of md-MTs in Cd detoxification of terrestrial snails, in general.
Highlights
Gastropods represent the most species-rich class within the phylum of Mollusca
The aim of this study is to evaluate the ability of A.b. to cope with Cd stress and the potential involvement of multi-domain MTs (md-MTs) in its detoxification
Following the findings of increased Cd-binding capacities in the three-domain MTs of Littorina littorea and Pomatias elegans, we suggest that the additional multiplication of N-terminal metal-binding domains in the MTs of Marisa cornuarietis and A. biplicata might increase their metal ion stoichiometry and their metal-binding capacity to a correspondingly high level
Summary
Gastropods represent the most species-rich class within the phylum of Mollusca. Throughout evolution, some gastropod lineages left their marine realms and colonized limnic and terrestrial habitats. A. biplicata is widely distributed in central Europe and can be found in forests, between rocks in urban areas (e.g., parks) or at riverside banks [1] It is one of the rare ovoviviparous snail species in which the whole embryonic development takes place inside the egg within the reproductive tract of the adult individual [2]. A proven strategy to overcome potentially stressful periods is its ability to switch to a state of inactivity, the so-called aestivation [3,4] Another protective feature of terrestrial snails is their ability to highly accumulate and inactivate toxic metal ions such as Cadmium (Cd) in their digestive organs and cells [5,6]
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