Fertilization: a sperm’s journey to and interaction with the oocyte
Masahito Ikawa, Naokazu Inoue, Adam M. Benham, Masaru Okabe
Masahito Ikawa, Naokazu Inoue, Adam M. Benham, Masaru Okabe
View: Text | PDF
Review Series

Fertilization: a sperm’s journey to and interaction with the oocyte

Abstract

Mammalian fertilization comprises sperm migration through the female reproductive tract, biochemical and morphological changes to sperm, and sperm-egg interaction in the oviduct. Recent gene knockout approaches in mice have revealed that many factors previously considered important for fertilization are largely dispensable, or if they are essential, they have an unexpected function. These results indicate that what has been observed in in vitro fertilization (IVF) differs significantly from what occurs during “physiological” fertilization. This Review focuses on the advantages of studying fertilization using gene-manipulated animals and highlights an emerging molecular mechanism of mammalian fertilization.

Authors

Masahito Ikawa, Naokazu Inoue, Adam M. Benham, Masaru Okabe

×

Figure 4

Potential mechanism of sperm-egg fusion.

Options: View larger image (or click on image) Download as PowerPoint
Potential mechanism of sperm-egg fusion. Sperm Izumo1 and egg Cd9 are es...
Sperm Izumo1 and egg Cd9 are essential factors for sperm-egg fusion (13, 16). GPI-anchored proteins on the egg surface are also essential (114), but none of the individual proteins have been identified. (A) Izumo1 is an acrosomal membrane protein that is not exposed before the acrosome reaction is complete. Acrosome-reacted sperm can be classified into three major groups by their Izumo1 staining pattern: acrosomal cap (B), equatorial (C), and whole head (D). (E and F) Cd9 is localized on the cilia distributed across the surface of unfertilized eggs, except the cilia at the metaphase plate. (G) Cd9-containing vesicles (asterisks) secreted from the oocyte are able to translocate onto the sperm surface and may play a role in sperm-egg fusion. G is reproduced with permission from Proceedings of the National Academy of Sciences of the United States of America (115).