Regulatory Plasticity of Earthworm wMT-2 Gene Expression

Abstract

Metallothioneins (MTs) are multifunctional proteins occurring throughout the animal kingdom. While the expression and transcriptional regulation of MTs is well-studied in vertebrates, the mechanism of MT activation is still unknown for most invertebrates. Therefore, we examined wMT-2 gene regulation and expression patterns in Lumbricus rubellus and L. terrestris. Transcription levels, the occupation of DNA binding sites, the expression of putative transcriptional regulators, and promotor DNA methylation were determined. We found that wMT-2 expression does not follow a circadian pattern. However, Cd-induced wMT-2 induction was observed, and was, interestingly, suppressed by physical injury. Moreover, the promotor region that is responsible for the wMT-2 gene regulation was elucidated. ATF, a putative transcriptional regulator, showed increased phosphorylation upon Cd exposure, suggesting that it plays a major role in wMT-2 gene activation. The promotor methylation of wMT-2, on the other hand, is probably not involved in transcriptional regulation. Elucidating the regulatory mechanism of the earthworm MT gene activation might provide insights into the molecular coordination of the environmental stress response in invertebrates, and might also reveal a link to wound repair and, in a broader sense, to immunity.

Effects of Cadmium Sulfate on the Brown Garden Snail Cornu aspersum: Implications for DNA Methylation

“…We also found that cadmium uptake via food had no effect on the methylation status of the Cd-MT gene 5 -region. Consistent with our findings, Drechsel et al observed no methylation in CG pairs of the Cd-inducible metallothionein gene wMT-2 promoter from the common earthworm, Lumbricus terrestris (Linnaeus, 1758), for both Cd-exposed and control individuals [45]. However, we cannot exclude a potential effect of Cd on the DNA methylation status of promoter or introns (non-coding regions) without examining in detail these regions of the Cd-MT gene.…”

High-level dietary cadmium exposure is associated with global DNA hypermethylation in the gastropod hepatopancreas

“…The Cd-MT gene contains CG sites [ 57 ], but there is no information available about their methylation status. In the common earthworm, Lumbricus terrestris (Linnaeus, 1758), a very recent study found no methylationin CG pairs of a selected promotor region of the Cd-inducible metallothionein gene wMT-2 even in the presence of cadmium exposure [ 58 ].However, the authors did not investigate the gene body region, which cannot eliminate a role of DNA methylation in the regulation of the wMT-2 gene or a potential effect of Cd on the methylation status of CG islands in the body of this gene. Such gene-based biomarkers may provide a reliable approach for detection of subtle effects of low-level Cd exposure, as has been already described in vertebrates [ 25 – 28 , 59 ].…”

Metallothioneins of the urochordateOikopleura dioicahave Cys-rich tandem repeats, large size and cadmium-binding preference

“…CREB, ATF-1, XBP1, E4BP4) might act also as activators of vertebrate MT genes, 69 and CRE binding sites have been identified in the promoter of earthworm MT genes. 70,71 Second, it has also been reported that transcription factors of the nuclear receptor family such as the steroid receptors, retinoid receptors and orphan receptors might be involved either directly (e.g. GR; 72 PPAR 56,57 ) or indirectly (e.g.…”