Stress induced Metallothionein transcription and regulation in earthworms

A variety of environmental stressors induce the expression of Metallothioneins (MTs), which mainly act as radical scavengers in oxidative stress response and detoxification of heavy metals. Earthworm MTs are widely used as biomarkers for metal pollution, however, the mechanism of MT gene activation is, however, largely unknown in most invertebrate species. Therefore, the present study aims to characterize the MT induction behavior upon Cd exposure and physical injury in two earthworm species (Lumbricus rubellus and L. terrestris). A basal MT transcription with no circadian pattern could be detected and a significant increase of MT gene expression was observed upon Cd exposure in a dose and time dependent manner. Interestingly, tip-cut earthworms did not show any MT transcription in controls or Cd exposed individuals. MT promoter studies revealed a member of the CRE binding protein family as putative transcriptional MT activator most likely in both controls and in heavy metal exposed earthworms. Additionally, MRE binding sites have been suggested to play a role in MT gene activation, although the typical MRE binding protein, MTF-1, is lacking in earthworms. The present study discloses novel information on MT gene transcription and its putative activation mechanisms. Moreover, we hypothesize that there might be a link between detoxification- and tissue repair mechanisms in earthworms.