Insect Vitellogenin: Identification, Biosynthesis, and Role in Vitellogenesis

Vitellogenins are defined as the predominant yolk protein precursors that are produced extraovarially and taken up by the growing oocytes against a concentration gradient. One of the most exciting aspects, and one that has attracted increasing attention during the last few years, is the mechanism of control of vitellogenin biosynthesis. This chapter focuses on the known control mechanisms that are amenable to experimental manipulation. The close analogy to the control mechanisms known for avian and amphibian vitellogenins makes research on insect vitellogenin even more rewarding. The chapter tabulates the identification of vitellogenin and vitellin according to the chronological documentation, the known species, grouped by orders, for which vitellogenins have been described. The very fact that only the female of the species contains a protein that is also the predominant yolk protein may allow speculating that ovaries transplanted into males may not incorporate yolk. However, as early as 1907 Meisenheimer found for the Lepidopteran Porthetria dispar that, larval ovaries transplanted into male larvae produced fully grown and chorionated eggs after metamorphosis. Contribution of non-specific proteins to protein yolk and uptake of haemolymph proteins by the oocytes have been discussed. The chapter discusses a model for endocrine controlled vitellogenin synthesis and vitellogenesis.