There is no author summary for this article yet. Authors can add summaries to their articles on ScienceOpen to make them more accessible to a non-specialist audience.
Abstract
Representing the 60 trillion cells that build a human body, a sperm and an egg meet,
recognize each other, and fuse to form a new generation of life. The factors involved
in this important membrane fusion event, fertilization, have been sought for a long
time. Recently, CD9 on the egg membrane was found to be essential for fusion, but
sperm-related fusion factors remain unknown. Here, by using a fusion-inhibiting monoclonal
antibody and gene cloning, we identify a mouse sperm fusion-related antigen and show
that the antigen is a novel immunoglobulin superfamily protein. We have termed the
gene Izumo and produced a gene-disrupted mouse line. Izumo-/- mice were healthy but
males were sterile. They produced normal-looking sperm that bound to and penetrated
the zona pellucida but were incapable of fusing with eggs. Human sperm also contain
Izumo and addition of the antibody against human Izumo left the sperm unable to fuse
with zona-free hamster eggs.