Previtellogenesis and Vitellogenesis

Early in the twentieth century, immunological techniques were used to pinpoint a specific antigen in the blood of gravid female fish during investigations on sex discrimination. The principal precursor of egg yolk protein, which is currently known as vitellogenin and is generated in the female liver before being secreted into the circulation and integrated into the egg, is currently identified as this particular antigen. The majority of the protein in yolk is made up of phosphoproteins and lipoprotein precursors. Vitellogenin serves as the wonderful provider and a component of the yolk, the key food to the developing embryos of egg layers (oviparous), including vertebrates and invertebrates. It transfers proteins and certain lipids from the liver through the blood to the maturing oocytes. Oocytes arrest in prophase I of the meiotic cell cycle, during which they expand as the building blocks for early embryonic development (vitellogenesis). In many vertebrates, fully grown postvitellogenic oocytes under prophase I arrest are unable to be fertilized until they mature. This current chapter focusses on a brief overview of previtellogenesis and vitellogenesis.