Gamete interactions in vitro

A method was devised that allowed observation of individual sperm in vitro in the presence or absence of unfertilized eggs. Sperm traversing microcapillary tubes in the absence of eggs moved in linear tranjectories. Sperm in the environs of unfertilized eggs moved in erratic paths, owing to repeated adherence of the sperm head to the wall of the microcapillary tube. However, translational velocity was unaltered. Increased adhesiveness was not noted when sperm were exposed to unfertilized eggs following removal of the cumulus oophorus with hyaluronidase. Gamete interactions in vitro were also studied at varying sperm to egg ratios. When gametes were mixed at high sperm to egg ratios (approximately 10⁶:1) the cumulus oophorus was rapidly dissolved, and sperm became adherent to the zona pellucida. At low ratios (approximately 10²:1), the cumulus oophorus remained intact. Binding of sperm to individual cumulus cells was noted. A hypothesis is presented that cumulus oophorus plays a role in fertilization by selectively trapping mature sperm within the perimeter of the egg and, in so doing, extending the duration of time in which gametes remain within close proximity, thus increasing the likelihood of egg contact by capacitated sperm.