The yolk proteins stored in Drosophila oocytes for utilisation during embryogenesis are an ideal system for studying the regulation of gene expression during development. The 3 major polypeptides found in yolk in D. melanogaster are synthesised in the fat body and ovarian follicle cells and selectively accumulated by the oocyte during vitellogenesis. In order to understand more about their regulation and the mechanism of uptake, studies on other species are necessary.
Three yolk polypeptides have previously been identified in the D. melanogaster sibling species (D. melanogaster, D. simulans, D. rnauritiana, D. erecta, D. teissieri, D. orena and D. yakuba). In D. melanogaster three genes located on the X chromosome are known to code for these yolk polypeptides. In this study genomic Southern transfers and in situ hybridisation experiments were carried out on the sibling species. Using the three cloned yolk protein genes from D. melanogaster, homologous sequences could be detected in the sibling species. It is suggested that three yolk protein genes occur in each of these species, all being located on the X chromosome, and that two of the genes are very closely linked in these same species. Yolk protein gene-homologous DNA sequences have also been identified in two more distantly related species D. funebris and D. virilis.