A FAT-BODY DERIVED PROTEIN IS SELECTIVELY SULFATED IN THE STICK INSECT OVARY BY TRANSCYTOSIS THROUGH THE FOLLICULAR EPITHELIUM

With the onset of vitellogenesis, the follicular epithelium overlying the oocyte in stick insect ovarioles becomes highly polarized and pate nt by formation of wide intercellular spaces. The aim of the present s tudy was to provide experimental support to the notion that the follic ular epithelium in this insect species may be involved in transcytosis . Data demonstrate that the follicular epithelium carries out sulfo-co njugation of a 85 kDa fat body derived protein by allowing it to trans it from one cell pole to another. Along the basal end, follicle cells branch into a number of cytoplasmic fingerlike projections. At the opp osite end facing the oocyte they taper off into lance-head shapes. Dif ferent vesicular elements are evident at both these extremities. In vi vo exposure to horseradish peroxidase shows that the vesicular element s present along the apical end provide an endocytic entry. In contrast , those present along the basal end are labeled with sodium [S-35]-sul fate, suggesting that they may be exocytic vesicles containing a sulfo -conjugated secretory product. In vivo exposure to sodium [S-35]-sulfa te caused radioactivity to appear over the Golgi apparatus and some ne arby vesicles of the follicle cell cytoplasm, including the exocytic v esicles. The intracellular pathway of the follicle cells was also exam ined by immunogold labeling using a monoclonal antibody raised against a 85 kDa fat body derived protein. Under these conditions, gold parti cles were consistently detected over the Golgi apparatus and the vesic ular elements lying along both poles of the follicle cell membrane. Ba sed on this evidence, it is concluded that follicular cells in stick i nsect ovarioles are endowed with the ability to undergo transcytosis b y providing an endocytic entry along the apical end and by releasing e xocytically a sulfo-conjugated 85 kDa protein along the base-lateral d omain of the follicle cell membrane. ((C) Elsevier, Paris).