Journal
JOURNAL OF EXPERIMENTAL ZOOLOGY PART A-ECOLOGICAL AND INTEGRATIVE PHYSIOLOGY
Volume 311A, Issue 10, Pages 776-787Publisher
WILEY
DOI: 10.1002/jez.564
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Funding
- Austrian Fonds zur Forderung der wissenschaftlichen Forschung [P19782-B02]
- French ANR (Agence Nationale de la Recherche) [ANR-05-ECCO-004]
- ADEME (Agence de l'Environnement et de la Maitrise de l'Energie) [0572C0058]
- Conseil Regional de Franche-Comte
- French program STARTT
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Gastropods are able to withstand fluctuating availabilities of nonessential trace elements such as cadmium by induction of Cd-specific metallothionein isoform. (Cd-MT) expression. As in other species, the induction mechanism involves the binding of metal-regulatory transcription factors (MTF-1 or MTF-2) to metal responsive elements (MREs) in the MT promoter regions. Cd-dependent transcription of Cd-MT genes was assessed by quantitative real time PCR in two helicid gastropods, Helix pomatia and Cantareus aspersus, over a period of eight days. The promoter regions of the Cd-MT genes of the two species were sequenced and compared regarding the position of MREs and other relevant potential transcription factor binding sites (TFBs). Cd-MT gene transcription is induced after Cd exposure in Helix pomatia and Cantareus aspersus, showing a transient peak in Helix pomatia, contrasting with a persistent induction rate in Cantareus aspersus. Since the existence of MTF-2 was verified in both species, differing transcription patterns of Cd-MT genes must be due to functional differences in their metal-responsive promoter regions. Both promoters contain a proximal cluster of three MREs overlapping with TFBs for the transcriptional regulator Sp1. In contrast to Cantareus aspersus, however, the Cd-MT gene of Helix pomatia hosts an additional distal MRE overlapping with a Sp1 binding site and a CACCC box. Inhibitory effects of MRE overlapping Sp1 binding sites were observed in other MT genes. We therefore suggest that transient Cd-MT transcription upon Cd2+ exposure in Helix pomatia may be the result of an inhibitory action of the distal MRE cluster. J. Exp. Zool. 311A:776-787, 2009. (C) 2009 Wiley-Liss, Inc.
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