Vitellin and Formation of Yolk Spheres in Vitellogenic Follicles of the Moth, Plodia in ferpunctella

Vitellin (Vt) was found not to be critical to the formation or structure of yolk spheres in oocytes of the moth, Plodia interpunctella (Hubner). Vitellogenic activities of the follicular tissues were determined by visualizing the immunocytolocalization of Vt subunits (YP1 and YP3) and of a follicular epithelium yollc protein (FEYP) subunit (YP2) in ultrathin sections or in whole-mounted tissues. Vitellogenin was detectable in the inter-follicular epithelial cell (FC) spaces of patent, vitellogenic follicles of normal females. When the follicles entered terminal growth phase, the inter-FC spaces closed equatorially around the follicle which excluded vitellogenin from that region. The closure of the spaces spread towards the poles in more mature follicles. Vt was immunolocalized to yolk spheres of vitellogenic and terminal growth phase oocytes. To examine the role of Vt in formation of yolk spheres, ovaries were transplanted into males. Vt was not detected in the inter-FC spaces, vitelline membrane, or yolk spheres of follicles from transplanted ovaries developing in males. However, the FEYP subunit YP2 was detected in the Golgi apparatus and secretory vesicles of columnar FC and in the yolk spheres of the oocytes from transplanted ovaries. During the late vitellogenic period, late yolk spheres appeared in the cortical region of the oocytes. In addition, YP2 was detected in the electron-translucent vitelline membrane of terminal growth phase follicles. We conclude that Vt is not required for the formation of yolk spheres or the electron-translucent layer of vitelline !membrane.