Measurement of annetocin gene expression: a new reproductive biomarker in earthworm ecotoxicology

The emergence of new technologies from the genomics revolution will transform the potential application of biomarkers to assess how pollutants impact people, animals, and ecosystems. Genetic databases provide a huge resource from which candidate molecular biomarkers can be identified and, subsequently, exploited to address these issues. However, a major challenge is to link these novel molecular indices to ecologically relevant whole-organism life-cycle traits (such as reproduction and growth). Such a functional link is provided by annetocin, previously characterized as a member of the vasopressin/oxytocin superfamily of neuropeptides. It is expressed in annelid worms within the neurons of the central nervous system and has been shown to be involved in the induction of egg-laying behavior. This paper outlines the validation of annetocin as a novel biomarker of reproductive fitness in the earthworm Eisenia fetida. The design of primer pairs targeted toward oligochaete annetocin has facilitated the isolation of a full-length annetocin cDNA from this species. Optimization of a real-time quantitative PCR procedure exploiting the fluorescent DNA-binding molecule, Sybr Green, has allowed the measurement of annetocin transcript levels over a range covering six orders of magnitude. Using this approach, gene expression was measured in earthworms exposed to soils polluted with high concentrations of zinc and lead. Traditional growth and reproductive indices, including cocoon production, were also recorded and related to the molecular parameter. The future use of annetocin as a molecular genetic biomarker in terrestrial ecotoxicology is discussed.