Morphodynamics of the contract plate in the course of oocyte maturation in the scyphozoan Aurelia aurita (Cnidaria: Semaeostomae)

摘要

The structure forming in the area of contact between the oocyte and the germinal epithelium in the course of oocyte maturation of the scyphozoan Aurelia aurita is termed the contact plate. This study traces the successive stages of contact plate formation in the course of oocyte maturation at the light microscopic and ultrastructural levels. At early stages of oocyte development, the appearance of granules is observed in the peripheral cytoplasm of the oocyte; these granules accumulate at the pole, which retains its connection with the germinal epithelium of the gonads. Two types of these granules are recognized: (1) granules with homogeneous content and (2) granules containing loose shapeless material in the form of thick cords. The transformation of type two granules into larger structures, as well as the consolidation of type one and type two granules at later stages of oocyte development, are probably the processes that lead to the formation of the characteristic structure and contact plate, visible in paraffin and semithin sections. It remains unclear where exactly the contact plate is localized at the moment of fertilization: inside or outside the oocyte. The content of granules and components of the plate specifically bind the antibodies (RA47) against mesoglein, the ZP domain-containing protein of the mesoglea of A. aurita. The contact plate, covering only the anomalous pole of the oocyte but detected by the presence of ZP domain-containing proteins, may prove to be the simplest egg membrane of the Zona Pellucida type.