Vitellogenin and Vitellin in Insects

Vitellogenin is the generic name for a unique group of proteins that are synthesized extraovarially and become the major egg yolk protein, vitellin. Similar proteins are found in all animals with yolky eggs. Because of their high concentration in the egg, and the relative ease with which they can be purified, these proteins are excellent material for the study of the regulation of their synthesis from the molecular, developmental, and physiological points of view. This review covers the synthesis, uptake, and physical and chemical properties of vitellogenins and vitellins in insects. The term vitellogenin was derived from vitellogenesis (102), the period of rapid oocyte growth during which yolk is deposited. Once inside the oocyte these proteins are known as vitellins, because in some cases the molecules are changed during uptake. The definition of vitellogenins has traditionally included the following criteria: (a) They usually comprise 60-90% of the soluble egg yolk proteins (13, 69); (b) they are not made the oocyte, the fat body being the site of synthesis (22, 69, 102); (c) are present in large amounts only in females and thus have been called female-specific proteins (11, 102), although rigorous techniques have revealed small amounts in males (83, 119) and so this definition is not exclusive; and (d) they are selectively taken up by the oocyte during vitellogenesis (120). Because of the dynamics of the uptake mechanism (112,