Multiple piscine vitellogenins: biomarkers of fish exposure to estrogenic endocrine disruptors in aquatic environments

Vitellogenin (Vg), a major estrogen-inducible yolk precursor protein, has become an important biomarker for assessing the estrogenic potency of chemicals and the exposure of animals to estrogenic contaminants present in aquatic environments. These contaminants, which can disrupt functioning of the vertebrate neuroendocrine system, are known as endocrine disrupting chemicals (EDCs). In general, investigations of the significance of estrogenic EDCs have failed to keep pace with recent developments in our understanding of vitellogenesis in fishes. Recent gene cloning and immunobiochemical analyses have verified the general multiplicity of piscine Vg and led to exploration of the unique roles of yolk proteins derived from different forms of Vg in the processes of oogenesis and embryogenesis. The levels of circulating Vg proteins (or Vg gene transcripts) during oogenesis and their degree of induction by estrogens appear to vary among species and among different types of Vg within species. The kinetics of induction of distinct types of Vg by estrogens in fishes appears to depend on environmental factors (e.g., water temperature and photoperiod), life history stage, and the concentration and type of estrogenic compound. Consideration of these findings will contribute to development of Vg-based bioassays superior to those currently based on the outdated "single Vg" model.