Regulation of Sperm-Egg Fusion at the Plasma Membrane
In fertilization, two types of gametes—sperm and egg—unite in a stepwise approach to create a single fertilized cell, which is capable of naturally developing into a new individual. Notably, membrane fusion occurring intercellularly between a sperm and an egg is essential for fertilization. In mammals, two integral membrane proteins, Izumo1 on the sperm plasma membrane and Cd9 on the egg plasma membrane, regulate sperm-egg fusion, and a new study has found a novel Izumo1 receptor, Juno, on the egg plasma membrane. Besides germ cells, Cd9 is expressed in a wide variety of cells, implying a close relationship between general fusion-related phenomena and sperm-egg fusion in particular. In invertebrate animals and in plants, Gcs1 plays an essential role in sperm-egg fusion. Considerable efforts are being devoted to understanding the molecular basis of cell-cell fusion; however, the exact mechanism(s) of the fusion process remain unclear. In this chapter we highlight the functions of some major molecules involved in the sperm-egg fusion and also discuss a possible molecular mechanism underlying this fusion.
KeywordsMembrane fusion Cd9 Izumo1 Juno Gcs1 Microvilli Tetraspanin Microexosome
This review was supported by a grant from The Ministry of Health, Labor and Welfare, and a grant-in-aid for Scientific Research, The Ministry of Education, Culture, Sports, and Technology of Japan. We have no conflict of interest.
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