Acrosome reaction induction in mammals

Sperm-egg recognition and binding is ensured by complementary sites on the gamete surfaces. ZP3, one of the glycoprotein components of the murine zona pellucida (ZP), functions both to bind acrosome intact sperm and to induce the acrosome reaction (AR) in bound, capacitated sperm. Pronase treatment of ZP3 yields small glycopeptides that bind to the sperm but do not cause ARs. If these bound glycopeptides are then treated with anti-ZP3 antibodies, the percent of sperm that undergoes the AR increases. The data suggest that the antibodies bind ZP3 which aggregates sites on the sperm head that cause the AR. A 15 kDa component of the sperm head, the acceptor, functions in ZP3 recognition.

This presentation attempts to define the acceptor's role in acrosome reaction induction in mouse sperm, and also to present a new staining technique for determining acrosomal status in mammalian sperm.

Capacitated murine sperm, when treated with SVI, which binds acceptor, and then with rabbit anti-SVI serum (anti-SVI), will AR. If anti-SVI Fab fragments were substituted for the immune serum, no increase in ARs occurred. If the sperm with bound anti-SVI Fab fragments were then treated with goat anti-rabbit IgG, the percentage of AR sperm increased.

If capacitated mouse sperm are treated with J-23, a monoclonal antibody to the acceptor, the percentage of ARs increased. If a control monoclonal antibody specific for the sperm head but not to the acceptor is added to capacitated sperm, the AR is not induced.

The data suggest that it is the aggregation of the bound acceptor that is the key to inducing the AR and that the acceptor and zona binding site are one in the same.

Since the acrosome plays such a major role in early events of fertilization, it is important to know its status. An acrosome staining technique previously used for mice was applied to human sperm. Transmission electron microscopy (TEM) was used to assess the accuracy of the Coomassie blue (CB) staining technique in determining acrosomal status of human sperm. Human sperm were treated with calcium ionophore to induce ARs and then were evaluated using CB and TEM. When the data were compared, the CB method positively correlated with the TEM ultrastructural examination.