Abstract
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.
Highlights
The presence of a protein found in female blood serum during oocyte growth in fishes was first reported in 1914 by Uhlenhuth and Kodama [1] in a paper entitled ‘A study of sexual distinction reaction’
In the 1940s, using the Tiselius method of electrophoresis, Deutsch et al [3, 4] and Moore [5] analyzed the electrophoretic patterns of serum proteins from several fish species and reported species differences
In our study using salmonids, in which no second proteolysis was observed, we revealed that three types of egg yolk proteins (Lv, Pv and β′-c) were subjected to separate degradations after fertilization, and that the degradation of LvH to smaller products and dephosphorylation of Pv occurred after the eyed embryo stage, while β′-c remained intact throughout embryo development [43]
Summary
The presence of a protein found in female blood serum during oocyte growth in fishes was first reported in 1914 by Uhlenhuth and Kodama [1] in a paper entitled ‘A study of sexual distinction reaction’. The complete Vtg (VtgA and/or VtgB) and incomplete Vtg (VtgC) have been successfully isolated and purified as two different proteins with distinct molecular weights and antigenicity in various fish species, including tilapia (O. aureus [85] and O. mossambicus [86]), medaka [87], Japanese goby Acanthogobius flavimanus [88] and Sakhalin taimen [89].
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