Hormonal and genetic regulation of vitellogenesis in Drosophila.

Morphological, genetic, and hormonal studies of the process of vitellogenesis, whereby yolk is accumulated in the developing oocytes, have been going on for many years in Drosophila. Recently there has been a resurgence of interest in vitellogenesis, for it provides a model system for investigating how eukaryotic genes are regulated. The proteins found in the yolk are regulated in a tissue-specific, stage-specific and sex-limited fashion. Molecular studies have identified the major proteins concerned and their genes have been cloned. This has facilitated a new approach to how this fascinating process is controlled. In this review current understanding of the factors required for normal vitellogenesis in Drosophila is analyzed. The nature of the proteins themselves, their sites of synthesis, and the organization and characterization of the genes and transcripts that code for them are emphasized. The manner in which the expression of these genes is regulated by the insect hormones, ecdysone and juvenile hormone, is described and, finally, an analysis is made of how various mutants that disrupt vitellogenesis can contribute further to our understanding of vitellogenesis regulation in Drosophila.