Zona pellucida in the process of fertilization and mammal embryonal development

In mammals, oocytes, fertilized eggs and pre-implantation embryos are surrounded by an acellular zona pellucida (zona pellucida – ZP). This structure has a fibro-spongy character but it undergoes constant modifications throughout its existence depending on many internal and external factors. ZP consists of glycoproteins marked as ZP1, ZP2, ZP3 and ZP4, the presence of which is species different. ZP1 and probably ZP4 molecules stabilize the fibrillary skeleton of the zona pellucida formed of ZP2 and ZP3 protein polymers which are ligands for specific spermatozoid receptors. The oligosaccharide chains of ZP3 are responsible for the primary attachment of the male gamete which induces the acrosomal reaction. ZP2 enhances this connection by secondary binding to an acrosome-free spermatozoid. Additionally, oviductal specific glycoprotein 1 which plays a role in interspecific oocyte-sperm interactions, appears around the postovulatory oocyte surrounded by ZP. In addition, this protein modifies the resistance of ZP to the action of proteases released as a result of the cortical reaction during polyspermia block. After fertilization, ZP not only protects the egg and then the embryo until implantation, but also has an embryotrophic effect. Understanding the molecular basics of the structure and properties of ZP can significantly improve animal fertility as well as reproductive rates.