Trans-order yolk protein can stimulate endocytic activity in Drosophila oocytes

Vitellogenins (Vgs) and mature yolk from some non-Dipteran insects can be recognized by Drosophila melanogaster oocyte Vg receptors and incorporated via receptor-mediated endocytosis into nascent yolk spheres (NYS). It had previously been assumed that only Vgs of Drosophila or other Dipterans could be so endocytosed. Drosophila ovarian follicles from 4-day old females were incubated in the presence of physiological salt solution (PSS) containing some fluorescent TexasRed-Dextran (Dex-red) or PSS-Dex-red in which either female hemolymph, or vitellin (mature yolk) from lysed oocytes was present from any of the following: (1) Drosophila (Diptera); (2) Oncopeltus (milkweed bug, Hemiptera); (3) Acteaus (luna moth, Saturniidae Lepidoptera); (4) Papilio (swallowtail butterfly, Papilionidae Lepidoptera); or (5) Xylocopa (carpenter bee, Hymenoptera). Under incubation conditions, any NYS would become fluorescent due to non-specific fluid-phase uptake. Ovarian follicles incubated in PSS-DexRed alone or in PSS with hemolymph from males did not carry out endocytosis detectable by this technique, but all other treatments listed above did.