Juvenile Hormone Induction of the Insect Yolk Protein Precursor

Abstract

In Leucophaea maderae the female specific protein, or vitellogenin, is being synthesized and secreted exclusively by the adult female fat bodies. This specific protein, which is induced by thejuvenile hormones makes up approximately 90% of the total yolk proteins. It is a lipophosphoprotein of low phosphorus (0.14‰) content. The female specific protein is synthesized on polysomes bound to membranes of the ergastoplasmic reticulum (ER). Microsome vesicles obtained from active tissues are heavily studded with ribosomes and are considerably more dense than those from “inactive” tissues. The nascent polypeptide chains of the vitellogenin are secreted into the cisternae of the ER and can be released by Na deoxycholate digestion of the membranes. Similarly, the non-specific serum proteins are also secreted into the cisternae of the ER. All evidence points to the fact that microsomes may carry mixed populations of polysomes, those associated with specific and those associated with non-sex-specific protein synthesis. The significance of the polysomal association with membranes for the synthesis of exportable sex-specific protein is discussed.