An Insight into the Roles of Zona Pellucida in Growth and Development of Mammalian Ocytes and Embryos: Changes of Age-related and Cryopreservation: A Review

The zona pellucida (ZP) is a extracellular transparent coat surrounding the oocyte and preimplantation embryo in mammals. The ZP separates between the surrounding cumulus cells and oocyte. It plays a pivotal role in oocyte growth and fertilization and early embryo development. Zona pellucida formation and glycoproteins, roles of ZP on female fertility and infertility, ZP micromanipulation on embryo development and changes of ZP upon vitrification of oocytes is discussed. Zona pellucida is formed of glycoproteins during ovarian follicle growth and development. It protects the oocyte from physical or chemical damage, initiates fertilization, prevents polyspermy and supports early embryonic development. The ZP is responsible for recognition between oocytes and sperm. Mutations in glycoproteins cause female infertility characterized by empty follicle syndrome and oocyte degeneration. The ZP removal is detrimental for embryo implantation. Furthermore, there is a biophysical role of ZP during vitrification of oocytes. Hence, the current review article was designed to collect, discuss and highlight the characters of zona pellucida, roles in female fertility and infertility, ZP micromanipulation on embryo development and changes of ZP upon vitrification.