Suppression of Non-Random Fertilization by MHC Class I Antigens

Hermaphroditic invertebrates and plants have a self-recognition system on the cell surface of sperm and eggs, which prevents their self-fusion and enhances non-self-fusion, thereby contributing to genetic variation. However, the system of sperm-egg recognition in mammals is under debate. To address this issue, we explored the role of major histocompatibility complex class I (MHC class I, also known as histocompatibility 2-K or H2-K and H2-D in mice) antigens by analyzing ( ) triple-knockout ( ) male mice with full fertility. sperm exhibited an increased sperm number in the perivitelline space of wild-type ( ) eggs in vitro. Moreover, sperm showed multiple fusion with zona pellucida (ZP)-free eggs, implying that the ability of polyspermy block for sperm from males was weakened in eggs. When male mice were intercrossed with female mice, the percentage of females in progeny increased. We speculate that eggs prefer fusion with sperm, more specifically X-chromosome-bearing sperm (X sperm), suggesting the presence of preferential (non-random) fertilization in mammals, including humans.