Physiological, Diurnal and Stress-Related Variability of Cadmium-Metallothionein Gene Expression in Land Snails

Abstract

The terrestrial Roman snail Helix pomatia has successfully adapted to strongly fluctuating conditions in its natural soil habitat. Part of the snail’s stress defense strategy is its ability to express Metallothioneins (MTs). These are multifunctional, cysteine-rich proteins that bind and inactivate transition metal ions (Cd2+, Zn2+, Cu+) with high affinity. In Helix pomatia a Cadmium (Cd)-selective, inducible Metallothionein Isoform (CdMT) is mainly involved in detoxification of this harmful metal. In addition, the snail CdMT has been shown to also respond to certain physiological stressors. The aim of the present study was to investigate the physiological and diurnal variability of CdMT gene expression in snails exposed to Cd and non-metallic stressors such as desiccation and oxygen depletion. CdMT gene expression was upregulated by Cd exposure and desiccation, whereas no significant impact on the expression of CdMT was measured due to oxygen depletion. Overall, Cd was clearly more effective as an inducer of the CdMT gene expression compared to the applied non-metallic stressors. In unexposed snails, diurnal rhythmicity of CdMT gene expression was observed with higher mRNA concentrations at night compared to daytime. This rhythmicity was severely disrupted in Cd-exposed snails which exhibited highest CdMT gene transcription rates in the morning. Apart from diurnal rhythmicity, feeding activity also had a strong impact on CdMT gene expression. Although underlying mechanisms are not completely understood, it is clear that factors increasing MT expression variability have to be considered when using MT mRNA quantification as a biomarker for environmental stressors.

Exposure to Dichlorodiphenyldichloroethylene (DDE) and Metallothionein Levels in Rats Fed with Normocaloric or High-Fat Diet: A Review

“…Conversely, in kidneys, the cytoprotective antioxidant machinery involves the ROS scavenger function of MTs, leaving the MT genes responsive to oxidative stress injury. Considering that MTs are often used as a biomarker of cellular damage following environmental pollution [24,27,60,61], these findings also underlined the importance of focusing on the appropriate tissues during biomonitoring studies and knowing the effective content of constitutive MTs in the analyzed tissues to avoid collecting misleading reports.…”

Light- and clock-control of genes involved in detoxification

“…at night) (Zhang et al, 2009). Previous research has also found diurnal rhythmicity in phase II conjugating glutathione-S-transferases and phase III transporters, including ATP-binding cassette transporter (ABC transporters) and metallothionein, although daily patterns vary between protein families (Pedrini-Martha et al, 2016;Zhang et al, 2009). Phase II enzymes also include other transferases such as sulfotransferases and nonconjugation enzymes, i.e.…”

Assessment of metallothionein expression in Biomphalaria alexandrina snails and Oreochromis niloticus Fish as a biomarker for water pollution with heavy metals.

“…These findings consistent with Dallinger et al(2004) who found that there is a strong correlation between heavy metals, particularly Cd accumulation, and MT concentration. As well, Pedrini-Martha et al (2016) reported that, MT genes can be up regulated in response to exposure to the corresponding metal ion. In addition, Roch et al (1982), Olsson and Haux (1986), Sulaiman et al (1991) and Hylland et al (1992) evidenced that an elevated level of MT in fish indicates that the fish has been exposed to heavy metals Pb,Cu and Cd.…”