title: The immunoglobulin superfamily protein Izumo is required for sperm to fuse with eggs.
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.
authors.affiliation: Genome Information Research Center, Osaka University, Yamadaoka 3-1, Suita, Osaka 565-0871, Japan.
authors.forename: Naokazu
authors.initials: N
authors.lastname: Inoue
authors.forename: Masahito
authors.initials: M
authors.lastname: Ikawa
authors.forename: Ayako
authors.initials: A
authors.lastname: Isotani
authors.forename: Masaru
authors.initials: M
authors.lastname: Okabe
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D006224:Cricetinae; D003433:Crosses, Genetic; D005260:Female; D017353:Gene Deletion; D006579:Heterozygote; D006720:Homozygote; D006801:Humans; D007136:Immunoglobulins / Q000737:chemistry* / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D007248:Infertility, Male / Q000235:genetics; D008297:Male; D008565:Membrane Proteins / Q000737:chemistry* / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D008969:Molecular Sequence Data; D010063:Ovum / Q000502:physiology*; D020554:Sperm Injections, Intracytoplasmic; D013084:Sperm-Ovum Interactions / Q000502:physiology*; D013094:Spermatozoa / Q000502:physiology*
chemical_list: C498176:IZUMO1 protein, human; D007136:Immunoglobulins; C498177:Izumo1 protein, mouse; D008565:Membrane Proteins