Abstract
Mammalian oocytes are surrounded by an extracellular coat called the zona pellucida (ZP), which, from an evolutionary point of view, is the most ancient of the coats that envelope vertebrate oocytes and conceptuses. This matrix separates the oocyte from cumulus cells and is responsible for species-specific recognition between gametes, preventing polyspermy and protecting the preimplantation embryo. The ZP is a dynamic structure that shows different properties before and after fertilization. Until very recently, mammalian ZP was believed to be composed of only three glycoproteins, ZP1, ZP2 and ZP3, as first described in mouse. However, studies have revealed that this composition is not necessarily applicable to other mammals. Such differences can be explained by an analysis of the molecular evolution of the ZP gene family, during which ZP genes have suffered pseudogenization and duplication events that have resulted in differing models of ZP protein composition. The many discoveries made in recent years related to ZP composition and evolution suggest that a compilation would be useful. Moreover, this review analyses ZP biosynthesis, the role of each ZP protein in different mammalian species and how these proteins may interact among themselves and with other proteins present in the oviductal lumen.
Highlights
The zona pellucida (ZP) is an extracellular matrix that is synthesized during follicular development and surrounds the plasma membrane of the oocyte and preimplantation embryo of mammals
This review outlines some of the progress that has been made in our understanding of the ZP during the last quarter of a century
What is the ZP structure like in species other than mouse, and is the sperm receptor the same in all species? Identification of the ZP protein responsible for binding to spermatozoa could be very useful in the development of fertility assays
Summary
The zona pellucida (ZP) is an extracellular matrix that is synthesized during follicular development and surrounds the plasma membrane of the oocyte and preimplantation embryo of mammals. The inner and outer layers presented a higher degree of birefringence than the intermediate region, which showed no birefringence. Bind to In sperm are the inner and outer layers presented a higher degree of birefringence than the intermediate still unknown. ZP inner regionregion was closer to the degree of birefringence followed by the outer region, whereas the intermediate region contrast, the most porous ZP region was in contact with the cells of the cumulus oophorus, showed little or no birefringence (Figure 1). Lectin histochemistry was used in the identification and characterization of the carbohydrates present in ovarian follicles, as well as in pre- and post-fertilized oocytes in a wide range of species Using this technique combined with enzymatic digestion and different chemical treatments, many authors suggested a heterogeneous glycoconjugate composition for the ZP [27,28].
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