Vitellogenesis and choriogenesis in fishes

In studies of sex discrimination in fish in the early 1900s, a specific antigen in the blood of gravid females was identified using immunological methods. At present, this specific antigen is known as vitellogenin, the major precursor of egg yolk protein that is synthesized in the female liver and is secreted into the blood to be incorporated into the egg. Recently, protein and gene analyses have revealed the presence of several vitellogenin variants. In addition, in the 1980s, choriogenin was identified as a novel precursor of egg envelope proteins that is secreted into the blood in response to stimulation by estrogen, similarly to vitellogenin. These two proteins not only play key roles in the process of oogenesis, but they are also used as effective biomarkers for assessing the impact of estrogen-like endocrine-disrupting chemicals (environmental hormones) in aquatic ecosystems.