What is a Zona Pellucida?
The zona pellucida, formerly called the zona striata, is a membrane surrounding an oocyte, or egg cell, made of glycoprotein. It binds sperm and is essential to the acrosome reaction, which helps a sperm penetrate the egg cell during fertilization. The zona pellucida contains a special glycoprotein, ZP3, that is responsible for these biological functions. An egg cell, like all animal cells, is surrounded by a plasma membrane, which protects the intracellular components and regulates what materials go into or out of the cell. The zona pellucida is located just outside the egg cell’s plasma membrane and is an important part of it. It is composed of three glycoproteins, ZP1, ZP2, and ZP3. ZP3 allows for species specific sperm binding, preventing the sperm of a different species from fertilizing the egg. ZP3 is especially important for animals that have external fertilization, such as fish. ZP2 mediates sperm binding, and ZP1 is important for the structural integrity of the zona pellucida.
