Vitellogenesis in Aquatic Animals

Vitellogenin (Vg) is the main precursor to egg yolk proteins (YPs) accumulated as nutrients for developing embryos of oviparous aquatic species. Recent gene cloning and immuno-biochemical analyses verified the presence of multiple Vgs in teleost fishes, similar to the case in chickens and Xenopus. These findings lead us to abandon the classical "single Vg model" and explore different functions of individual Vgs and their YP derivatives during teleost oocyte maturation and embryogenesis. The course of proteolysis of Vgs and their YP products appears to differ among species. Detailed characterization of the relevant proteolytic enzymes has been partly accomplished only for salmonid fishes. Investigations of the endocrine regulation of teleost Vg and YP proteolysis have only just begun. Over the past decade, much attention has been paid to Vg due to its promise as a biomarker of contaminants that mimic estrogen, which are present in the aquatic environment. Sensitive and specific assays for measuring Vg in male and juvenile fish have been and will be valuable tools for identifying environmental estrogens to which humans and wildlife are potentially exposed.