Ultrastructure of the Hamster Zona Pellucida Treated with Zona Precipitating Antibody

The ultrastructure of the zonae pellucidae of hamster ova after treatment with zona precipitating antibody (ZPA) was investigated. The hamster zona as viewed by transmission and scanning electron microscopy reveals an intricate network of interconnecting fibers. This network of interstitial zona fibers results in the formation of a porous outer zona region adjacent to a more compact but porous inner zina. The canaliculi bounded by these fibers provide viaducts by which processes of follicular cells may pass through the zona and interact with the vitelline surface. ZPA treatment of zonae results in the interaction of the specific immunoglobulins with the fibrous network of the outer region but does not occlude the interstitial pores. The pattern of ZPA-zona interaction greatly accentuates the substructure of the outer zona and resembles a layer or aggregations of fine to medium-course granules and/or electron dense particles which can be observed as a dense precipitate with the light microscope. Treatment of zonae with control media, preimmunization serum or ZPA absorbed with ovary, does not produce a zona precipitate. These zonae when viewed with the electron microscope lack the distinct, dense precipitate observed in ZPA-treated zonae. In view of the pattern of ZPA interaction with the fibrous components of the zona and the lack of pore occlusion, ZPA may in fact block or mask sperm receptors and/or enzyme substrate(s) during sperm penetration or mechanically inhibit zona dissolution during implantation.