Vitellogenesis in the stick insect Carausius morosus (Br.) has been studied with the goal of identifying vitellogenin in various tissues. Following exposure to in vivo to radioactive amino acids, oocytes in the medium size range are labelled with a minimum delay of 6 h after the time of injection. Incorporation of radioactivity under these conditions is shown to depend upon accumulation of proteins rather than on a differential rate of protein synthesis in succeeding stages of oogenesis. By immunochemical analyses, it is shown that at least two antigens are common to both haemolymph and ovary and that one of these is also present in the fat body. Both antigens are labelled during exposure to radioactive amino acids. When analysed by the SDS polyacrylamide gel electrophoresis, extracts from both haemolymph and ovary appear to share a number of protein fractions which range in molecular weight from 40 000 to 200 000 Daltons. The labelling pattern exhibited by these fractions is clearly indicative of a protein transfer from the fat body to the oocyte. Fat body cultured in vivo for up to 4 h releases a major macromolecular complex in the external medium. The latter has been identified as vitellogenin by both immuno-precipitation assay and SDS polyacrylamide gel electrophoresis. The protein which is synthesized and secreted under these conditions results from the processing of a protein complex of higher molecular weight.
A Fat Body-Derived Protein Is Selectively Sulfated during Transit to Ovarian Follicles in the Stick Insect Carausius morosus