Mouse sperm antigens that participate in fertilization. IV. A monoclonal antibody prevents zona penetration by inhibition of the acrosome reaction.
To investigate the molecular basis of gamete interaction in mammals, monoclonal antibodies (mAbs) have been generated by syngeneic immunization with mouse testis. Previous work has described two particular mAbs, M41 and M42, which localize indistinguishably to the plasma membrane overlying a restricted portion of the acrosome, but recognize different antigens. One of the mAbs, M42, inhibits mouse fertilization in vitro significantly, but only in the presence of the zona pellucida, whereas M41 has no apparent effect upon any assayable event in the fertilization process. The experiments described here were performed to identify the precise event of sperm-zona interaction (sperm-zona binding, induction of the acrosome reaction, or penetration through the zona) that is affected by M42 mAb. Capacitated mouse sperm binding to the zona pellucida was undiminished following pretreatment with M42 mAb, when compared to levels achieved using either no mAb- or to M41 mAb-treated control sperm. When the effect of mAbs on the zona-induced AR was examined, the percentage of acrosome reacted (AR) sperm at the zona surface increased with time, plateauing at approximately 90 min post-insemination, with 78% of the bound cells AR in the control and the M41 mAb-treated groups. M42-treated sperm never achieved greater than 23% AR cells over the 120-min interval assayed. To quantitate this effect, capacitated sperm were exposed to increasing concentrations of acid-solubilized zonae. Increased proportions of AR sperm were found in the control and M41 mAb-treated groups, up to a maximum of 70-76% AR cells with 8 or 12 zonae/microliter. In contrast, M42-treated sperm displayed only 21-28% AR cells over the entire range of zonae concentrations tested. An entirely different result emerged when acrosome reactions were induced with A23187: M42 was no longer able to prevent the AR. This ability of A23187 to override M42 mAb's inhibitory effect on the AR permitted specific examination of the possible effect of M42 mAb on sperm penetration through the zona pellucida. In the presence of A23187, zona penetration levels for M42 mAb-treated sperm were equivalent, both qualitatively and quantitatively, to control and to M41 mAb-treated sperm under the same conditions. It appears, therefore, that M42 mAb identifies a high molecular weight doublet (220-240 kDa) of mouse sperm that participates specifically in the induction of the sperm's acrosome reaction as it occurs under physiological conditions.
D000177:Acrosome / Q000502:physiology; D000818:Animals; D000911:Antibodies, Monoclonal; D000001:Calcimycin / Q000494:pharmacology; D005260:Female; D005306:Fertilization / Q000187:drug effects; D008297:Male; D051379:Mice; D013084:Sperm-Ovum Interactions / Q000187:drug effects; D013094:Spermatozoa / Q000276:immunology / Q000502:physiology*; D015044:Zona Pellucida / Q000276:immunology
D000911:Antibodies, Monoclonal; D000001:Calcimycin