Physical Properties of the Zona Pellucida

The zona pellucida (ZP) is the extracellular coat that surrounds the mammalian oocyte. It forms a spherical shell of remarkably uniform thickness (5-10 mm in eutherian mammals) composed of three glycosylated proteins (ZP1, ZP2 and ZP3). Penetration of this shell by spermatozoa plays a crucial role in mammalian fertilization and any inability of spermatozoa to penetrate the ZP inevitably leads to infertility. The purpose of this work is to shed light to the three-dimensional structure of the ZP, its construction and its properties as a polymer. By means of the Atomic Force Microscopy (force-distance curves) we have determined for the first time several ZP structural properties (elasticity, plasticity, adhesion, etc.) during the ovulatory, periovulatory and fertilized phase. Moreover information about single polymers interactions has been obtained by means detachment experiments (pull-off curves).