Comparative developmental physiology and molecular cytology of the polytrophic ovarian follicles of the blowfly Sarcophaga bullata and the fruitfly Drosophila melanogaster.

1. The ovarian follicles of Sarcophaga and Drosophila consist of one oocyte and 15 nurse cells, the whole being surrounded by follicle cells. Although oocyte and nurse cells are genetically identical sibling cells, and although they are interconnected by cytoplasmic bridges, their physiology is very different. 2. The DNA content of the oocyte nucleus (germinal vesicle) never exceeds 4C, while values of polyploidisation up to 1024C have been measured in the nurse cells, this being dependent on their position within a follicle. 3. The nurse cell nuclei very actively synthesize RNA, while the germinal vesicle is almost completely inactive in this respect. 4. It has been possible to visualise the major cytoskeletal elements in the different ovarian cell types. Cellular markers of polarity and dorsoventral asymmetry have been described. 5. Electrophysiological measurements have been performed to find out whether or not the self-electrophoresis principle may be involved in polarised transport between nurse cells and oocyte. 6. Most of the vitellogenin is synthesized by the fat body but some follicle cells also synthesize small amounts. 7. The role of 20-OH ecdysone in the induction of vitellogenin synthesis in the fat body, as well as the presence of met-enkephalin like immunoreactivity in the gonads is well established in both species. Not so clear is the exact role of juvenile hormones and the nature of brain factors controlling ovarian development. 8. Drosophila has the advantage of its well documented genetics while the larger species Sarcophaga is preferable for the study of (electro-) physiological and cell biological mechanisms.