What is a description of the process of vitellogenesis?

Answer 1

Vitellogenesis(also known as yolk deposition)is the process of yolk formation via nutrients being deposited in the oocyte, or female germ cell involved in reproduction. It starts when the fat body stimulates the release of juvenile hormones and produces vitellogenin protein. It occurs in all animal groups lower than the mammals. In cockroaches, for example, vitellogenesis can be stimulated by injection of juvenile hormone into immature females and mature males. 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.