Autonomous yolk protein synthesis in ovaries ofDrosophila cultured in vivo

Immature ovaries ofDrosophila mercatorum were injected into young larvae and into adult males ofD. mercatorum, D. melanogaster, D. hydei, D. virilis, andZaprionius vittiger. These homo- and heteroplastic transplantations allow normal vitellogenesis to occur in the donor ovary. By SDS gel electrophoresis, we identified the major species-specific yolk proteins of mature eggs (stage 14) which were exclusively of donor-specific origin. Other experiments withD. hydei andZ. vittiger showed that, when females were used as hosts, the host-specific yolk proteins became incorporated into the donor eggs. When two immature ovaries, one ofD. mercatorum and one ofD. hydei, were co-cultured in males, again only the donor-specific yolk proteins were found in the mature eggs implying that these yolk proteins were not released into the host hemolymph.A parthenogenetic strain ofD. mercatorum was used to demonstrate the ability of transplanted immature ovaries to produce viable eggs which can give rise to fertile adults.The role of the species-specific yolk proteins is discussed with respect to the dual origin of these proteins during normal vitellogenesis, i.e., an autonomous synthesis within the ovary itself in addition to the well-known production by the fat body. Further experiments with pupae as hosts indicate that even in the absence of juvenile hormone and in the presence of high doses of ecdysone, vitellogenesis can proceed within the donor ovary.Based on these experiments, a new hyopthesis on the hormonal control of vitellogenesis inDrosophila is presented. We propose that yolk proteins derived from the fat body are controlled by juvenile hormone, whereas the independent and autonomous vitellogenesis within the ovary itself is controlled by endogenously synthesized ecdysone.